UC-NRLF 
 
 SB 33 DMD 
 
MOTOR TRUCK DESIGN 
 AND CONSTRUCTION 
 
MOTOR TRUCK DESIGN 
 AND CONSTRUCTION 
 
 BY 
 
 C. T, SCHAEFER 
 
 CONSULTING ENGINEER 
 MEMBER SOCIETY OF AUTOMOTIVE ENGINEERS 
 
 292 ILLUSTRATIONS 
 
 NEW YORK 
 
 D. VAN NOSTRAND COMPANY 
 
 25 PARK PLACE 
 
 1919 
 
S3 
 
 COPYRIGHT, 1919, BY 
 D. VAN NOSTRAND COMPANY 
 
 PRESS OF 
 
 THE NEW ERA PRINTING COMPANY 
 LANCASTER, PA. 
 
PREFACE 
 
 This volume has been written to fill a pressing want ; to 
 give a practical discussion of the gasoline propelled com- 
 mercial car of the present type, and to present this subject 
 in the plainest possible manner by the use of numerous 
 illustrations. In other words, this work is compiled for the 
 engineer, who, when he desires information on current 
 practice, may quickly obtain the same without a general 
 study. At the same time a general outline of the underlying 
 principles is given for the student, commercial vehicle 
 owner and operator who may desire to familiarize himself 
 with the construction of the various units that make up the 
 complete vehicle. 
 
 The author feels confident that he has been successful 
 in the production of a serviceable treatise on the subject of 
 Motor Truck design and construction. 
 
 C. T. SCHAEFEK. 
 
 ANDERSON, IND., 
 Sept. 1, 1919. 
 
 415370 
 
CONTENTS 
 
 CHAPTER. PAGE. 
 I. THE GENERAL LAYOUT OF THE CHASSIS , 1 
 
 II. THE MOTOR TRUCK ENGINE, ITS CONSTRUCTION AND LUBRICA- 
 TION 6 
 
 Two and Four Cycle Motors, Cylinders, Crank Case, etc., 
 and their Functions. 
 
 III. THE MOTOR COOLING SYSTEM 39 
 
 Air and Water Cooling-, Natural and Forced Cooling 1 Sys- 
 tems. Radiators and their Mounting. 
 
 IV. CARBUBETION AND CARBURETORS 50 
 
 Control and Vaporization of Fuel. 
 
 V. IGNITION SYSTEMS 59 
 
 High Tension, Low Tension and Inductor Magnetos. Bat- 
 tery and Igniter Systems. 
 
 VI. GOVERNORS AND SPEED CONTROLLING DEVICES 85 
 
 Centrifugal, Hydraulic and Automatic Governors. 
 
 VII. THE CLUTCH AND TRANSMISSION 95 
 
 Cone, Multiple Disc, and Dry Plate Clutches. Friction, 
 Planetory, Progressive Sliding and Selective Sliding 
 Transmissions. 
 
 VIII. UNIVERSAL JOINT AND PROPELLER SHAFT 114 
 
 Mechanical and Fabric Type Universals. Solid and Tubu- 
 lar Shafts. Propeller Shaft Bearing Mounting. 
 
 IX. THE DIFFERENTIAL 125 
 
 Spur, Bevel and Worm Gear Types. 
 
 X. THE FINAL DRIVE 132 
 
 Open and Enclosed Chain Drive. Bevel, Double Reduction, 
 Internal and Worm Gear Drive Axles. Method of taking 
 Torque and Propulsion. The Hotchkiss Drive. 
 
 XI. FRONT AND FOUR WHEEL DRIVES 162 
 
 Tractors, Gasoline and Electric Types. 
 
 XII. MOTOR TRUCK BRAKES 172 
 
 Internal and External Types. Jack Shaft, Propeller Shaft, 
 and Rear Wheel Types. 
 
 XIII. THE FRONT AXLE 183 
 
 Elliot, Lemoine and Reversed Elliot Steering Knuckles. 
 Drop Forged and Built-Up Types. 
 
 vii 
 
viii MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 CHAPTER. PAGE. 
 
 XIV. STEERING GEARS AND FUNDAMENTAL PRINCIPLES OF STEERING 
 
 MECHANISMS 192 
 
 Spur, Bevel and Worm Gear, Screw and Nut Types. Steer- 
 ing- Gear and Linkage. Construction and Layout. 
 
 XV. MOTOR TRUCK FRAMES 210 
 
 Structural and Pressed Steel, Rigid and Flexible Types. 
 
 XVI. POWER PLANT MOUNTINGS 220 
 
 Unite Power Plant, Individual Mounting, Sub Frame 
 Mounting. Three and Four Point Suspension. 
 
 XVII. SPRINGS AND SPRING SUSPENSIONS 230 
 
 Spring Types, France and Axle Mountings. Overload and 
 Auxiliary Spring's. 
 
 XVIII. THE FUEL SUPPLY SYSTEM 244 
 
 Gravity, Pressure and Vacuum Systems. Gasoline Tank 
 Construction and its Mounting-. 
 
 XIX. CONTROL 253 
 
 Spark and Throttle Control, Clutch and Brake Pedal 
 Mounting 1 . Gear Shift and Brake Control Systems. 
 
 XX. THE MUFFLER 265 
 
 Muffler Construction and Cut Outs. 
 
 XXI. MOTOR TRUCK WHEELS 272 
 
 Wood, Pressed and Cast Steel Types, for Single and Dual 
 Types. 
 
 XXII. MOTOR TRUCK TIRES AND RIMS 280 
 
 Side Flange, Demountable, S. A. E. std. Pressed-on Single 
 and Dual Types. American and European Sections. 
 Care of Motor Truck Tires. 
 
 XXIII. ELECTRIC LIGHTING AND STARTING ON COMMERCIAL VEHICLES. 298 
 Advantages and Disadvantages of Electrically Equipped 
 Trucks. 
 
MOTOR TRUCK DESIGN AND 
 CONSTRUCTION 
 
 CHAPTEK I 
 
 THE GENERAL LAYOUT OF THE CHASSIS 
 
 ANY commercial vehicle conforming to the accepted stand- 
 ard of construction may be divided in two parts, the chassis and 
 the body. The chassis or running gear as it is sometimes called, 
 consists of the frame, power plant, springs, axles, wheels, brakes 
 and in fact all units which enter into the propulsion and control 
 of the vehicle. 
 
 There are three general types of chassis when classified ac- 
 cording to the type of power plant, the gasoline, the steam and 
 the electric. The gasoline propelled vehicle is by far the most 
 popular and will be considered in this work. 
 
 The general layout of the chassis covers such points as the loca- 
 tion of the driver's seat or cab in relation to the location of the 
 power plant, which controls the distribution of the useful or pay 
 load of the vehicle. This affects the overall length and turning 
 radius of the vehicle. 
 
 The principal problem confronting the commercial vehicle 
 designer is how to make use of the overall length of the chassis 
 to the best advantage, considering accessibility and all other 
 factors which enter into this problem. 
 
 Most designers have placed the driver's seat back of the motor. 
 This necessitates the making of the total length of the machine 
 somewhat greater than it would be for the same capacity when 
 the driver's seat is placed above the motor. In some cases a com- 
 promise is effected between these two by placing the driver's seat 
 and steering to the right or left side of hood which encloses the 
 motor, thus saving about half the space used in the design which 
 has the seat placed in back of the motor. 
 
 Advocates of each type have a number of arguments in favor 
 of their design, all of which have merit. The one who places the 
 2 1 
 
fcB: ESIGN AND CONSTRUCTION 
 
 seat over the motor, claims that by this arrangement, the load is 
 shifted somewhat forward and the center of gravitjr is brought 
 somewhat nearer the center of the machine. This is claimed to 
 create more even tire wear all around and a reduction of the total 
 overall length of the chassis. The last is an advantage as it per- 
 mits a shorter wheel base and turning radius. 
 
 Those who place the seat back of the motor claim that in the 
 above construction too much weight is placed on the front axle, 
 that the motor is more accessible and that it is placed in a higher 
 position in the frame. The front springs can be made somewhat 
 lighter, since they are not required to carry as large a percentage 
 of the total load. And being lighter, they are less stiff and take 
 the shocks of the road more readily, which tends to increase the 
 life of the motor. These widely varying views of the makers are 
 echoed in many different lengths of commercial vehicles which 
 have been placed on the market. 
 
 Probably no single feature of commercial car design merits 
 more attention than does that of arranging the power plant in 
 such a manner as to offer the user motor accessibility in the great- 
 est degree consistent with reasonable compact design. The im- 
 portance of the first desideratum will be admitted by anyone 
 having experience in the operation of an internal combustion 
 engine. The day is still far distant when a gasoline engine may 
 be locked in a box and with a supply of essence, be expected to 
 mote satisfactorily until like the justly famous Shay, its multi- 
 tudinous parts give out simultaneously as a result of legitimate 
 wear. The desirability of compact arrangement will be endorsed 
 as a purely academic proposition and will be heartily subscribed 
 to as a thoroughly practical feature by truck operators, who have 
 had to deal with metropolitan street and garage conditions. 
 
 As far as the power plant arrangement is concerned American 
 makers have formed themselves into three distinct classes. First, 
 the class comprising those who place accessibility above all other 
 considerations. Second, the class comprising those whose great- 
 est satisfaction arises from the contemplation of a design in 
 which the compact arrangements of parts is accentuated. Third, 
 the class comprising those who have attempted to effect a com- 
 promise between the above two types, to secure both accessibility 
 and compactness. 
 
 Advantages of Placing Motor Under the Hood. A layout of 
 the trend of the first class of commercial car design is depicted in 
 
THE GENEEAL LAYOUT OF THE CHASSIS 3 
 
 Fig. 1. It will be noted that the motor is carried under a re- 
 movable hood in front of the driver's seat and control elements, 
 being typical of current passenger car chassis design. The load- 
 ing platform is divided into approximately equal parts fore and 
 aft of the rear axle. This design permits of easy access to the 
 motor and accessory parts from both sides and top, making it 
 
 FIG. 3. 
 THREE PROMINENT TYPES OF CHASSIS. 
 
 equal in point of accessibility to passenger cars. The driver's 
 seat is also accessible while the clutch and change gear can be 
 easity reached through the floor board opening when they form 
 a unit with the motor. The greater percentage of the paying 
 load is concentrated upon the rear or driving wheels, resulting in 
 good traction and easy steering. This construction also results 
 in a pleasing appearance, which is of some advantage in smaller 
 vehicles, which are used to some extent as an advertising feature. 
 
4 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 Disadvantages of this Type. Like all other constructions the 
 above type offers certain disadvantages. The overall length of 
 the vehicle must be greater in order to permit the location of the 
 motor under a removable hood. In many cases this added length 
 does not operate as a decided disadvantage for average applica- 
 tion in which the machine must be maneuvered, in narrow thor- 
 oughfares, backed up to curbings and garaged in valuable space, 
 every inch of added length makes itself felt in the owner's purse. 
 With the question of load distribution it may be said that care- 
 less freight handlers are just as likely to place the light, bulky 
 portion of a miscellaneous load forward of the axle, and to burden 
 the overhang with heavy material, occupying little space, as they 
 are to reverse the loading. Concentration of both driving and 
 load stresses to a maximum degree upon one pair of tires causes 
 loss as far as tire economy is concerned. 
 
 Motor Under the Seat Type. Turning now to the type of con- 
 struction representative of the second class of design, we find 
 illustrated in Fig. 2, a vehicle in which the driver's seat and con- 
 trolling elements are superimposed upon the motor space, the 
 load being apportioned fore and aft the rear axle in an approxi- 
 mate ratio of 2 to 1. The result of this load distribution is that 
 it does not permit of a traction ratio so high as does the pre- 
 viously described type, and steering is perhaps less sensitive. 
 But when the high friction coefficient of rubber is considered 
 upon average road surface and the fact that roller bearing steer- 
 ing heads are to be found in most commercial car axles of mod- 
 ern design, then these two conditions become relatively important. 
 In respect to the load distribution, the latter construction pos- 
 sesses advantages over the first type. For a given loading space 
 the construction in Fig. 2 permits of marked compactness in 
 overall length, with the attendant advantage of ease of handling, 
 minimum projection into through fares when backed up to a 
 curve and economy of garage space. 
 
 Lack of Accessibility. These relative advantages are gained 
 at the expense of motor accessibilit}^ Doors or removable panels 
 are usually fitted to allow access to the motor from the side, 
 while floor boards permit limited access from the top. When 
 front fenders are provided the access from the sides is also ma- 
 terially reduced. This notable lack of accessibility arises, first, 
 from the necessity for rigid and fairly bulky superstructure for 
 carrying the driver's seat and second, from the fact that a maze 
 
THE GENERAL LAYOUT OF THE CHASSIS 5 
 
 of control levers, brackets and rods are frequently located in the 
 space which should be reserved for access to the motor and its 
 accessories. Many trucks show a marked improvement in this 
 construction, however, at best it leaves much to be desired in the 
 way of accessibility. 
 
 Type Three a Combination. There is still another type, Fig. 
 3, which has been introduced several years ago, in which an 
 attempt is made to combine the advantages of the first and sec- 
 ond types is apparent. This has been accomplished in a meas- 
 ure, by mounting the motor in a more or less accessible position 
 between the two seats. A removable hood is generally fitted, but 
 the net result is almost invariably inferior from a standpoint of 
 accessibility to the construction shown in Fig. 1, although from 
 the same viewpoint it is an improvement over Fig. 2. The ad- 
 vantage of longitudinal compactness is retained, moreover the 
 weight is well distributed between the front and rear axles. 
 
 In making the illustrations, the writer has taken pains to have 
 the wheel base (i. <?., center of front wheel to center of rear 
 wheel), and the length of the loading in equal proportions in all 
 illustrations so that a good idea can be obtained as to relative 
 overall length and weight distribution. 
 
 It can readily be seen that in the point of overall length, the 
 construction which embodies placing the driver's seat over the 
 motor has the advantage of requiring less length than the other 
 two types. While, on the other hand, the question may be asked, 
 are the advantages to be gained by placing the driver's seat over 
 the motor great enough to outweigh those claimed for other con- 
 structions 1 
 
 The general advantage of either construction presents itself 
 when the conditions of operations are considered. The vehicle 
 may be operated in districts when traffic is congested, which 
 would favor class two, while on the other hand accessibility may 
 be the chief point to be considered, which then would favor class 
 one. While certain conditions may suggest the selection of class 
 three. In the smaller vehicles class one is greatly desired owing 
 to its pleasing appearance when fitted with expense bodies. 
 
 From the above it can readily be understood that the construc- 
 tion of a vehicle is somewhat depended upon the conditions of 
 operation and nature of the work it has to accomplish. 
 
CHAPTEE II 
 
 THE MOTOR TRUCK ENGINE ITS CONSTRUCTION AND 
 LUBRICATION 
 
 Two and Four-cycle Multi-cylinder Motors. This term cycle 
 is defined as the cycle of operations or, in other words, the suc- 
 cessive actions of the working fluid of a heat engine upon the 
 piston and of the piston upon the working fluid commencing 
 when a certain relationship between the two exists and ending 
 with the next recurrence of the same relationship; or, in other 
 words, any series of events occurring in succession, which goes to 
 make up a complete operation. 
 
 . There are four things which must occur in an engine cylinder 
 in succession before it can repeat. As soon as the explosion oc- 
 curs, the gas must expand, which forces the piston down to the 
 end of its stroke. Upon the completion of this stroke or the next 
 up stroke the spent gases must be gotten rid of by forcing them 
 out of the cylinders; then a fresh charge must be drawn in and 
 compressed before the explosion again takes place. 
 
 This series of operations is termed the cycle of operations. 
 There are two types of gasoline motors, one comprising that type 
 which has a power stroke every revolution, which is termed the 
 two-cycle or two-stroke type, and the other which has a power 
 stroke every other revolution, termed the four-cycle or four- 
 stroke type. 
 
 The Two-cycle Type. As mentioned above, the characteristic 
 feature of the two-cycle motor is that there is an explosion every 
 revolution on the down stroke of the piston. Another feature of 
 this type of motor is that the gas must be precompressed, which 
 is generally accomplished by admitting it to the crank case before 
 it reaches the cylinders. 
 
 There are two general types of two-cycle motors, known as 
 the two- and three-port types, so called, by the number of ports 
 in the cylinders, which permit gas to enter and to escape after 
 combustion. The three-port type is mostly used in motor truck 
 work, while the two-part type is strictly a low-speed motor and 
 best adapted to marine work, where speed is a minor considera- 
 
 6 
 
THE MOTOK TRUCK ENGINE 7 
 
 tion. In depicting the operations of a two-cylinder motor, the 
 three-port type will be considered, as it would be useless to use 
 considerable space on a subject which is of no interest. 
 
 In four-cycle motors the four events mentioned above, i.e., 
 ignition, exhaust, intake and compression, take place between the 
 piston head and the head of the cylinder, but in the two-cycle 
 type the crank case is made air tight and performs part of the 
 work of getting the gas ready to ignite. 
 
 The successive operations of the two-cycle motors are as fol- 
 lows: While the piston is traveling upward in the cylinders it 
 creates a partial vacuum in the crank case, and when it reaches 
 a certain point it uncovers the intake port A in the walls of the 
 
 CYCLE OF OPERATIONS IN A Two CYCLE MOTOR. 
 
 FIG. 4. FIG. 5. FIG. 6. 
 
 Crank Case In- Expansion and Exhaust and 
 
 let and Cylinder Exhaust. Transfer of 
 
 Compression. Gas. 
 
 cylinder, through which, by reason of this vacuum, it permits a 
 charge of gas to enter the crank case from the carbureter. This 
 stroke is illustrated in Fig. 4, while Fig. 5 depicts the next down 
 stroke of the piston. Daring this down stroke, the charge is 
 partly compressed in the crank case. As the piston reaches the 
 bottom of its stroke, it uncovers the port B in the cylinder wall, 
 which communicates with the crank case and is called the transfer 
 port, thus permitting the charge in the crank case to enter the 
 cylinder. Shortly after the piston starts on its up stroke it closes 
 this transfer port, and during the remainder of this stroke the 
 charge is compressed within the cylinder and as it reaches the 
 top of its stroke the charge is ignited, expands and forces the 
 piston downward. As the piston reaches the bottom of its stroke 
 the exhaust port C is opened, and the spent gases which are still 
 
8 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 under considerable pressure escape through this port. This ex- 
 haust port opens a trifle earlier than the transfer port, permit- 
 ting considerable of the spent gases to escape before the fresh 
 charge is admitted to the cylinders. This is illustrated in Figs. 5 
 and 6. It is, of course, impossible to completely scavenge the 
 cylinders and prevent the fresh charge from escaping through 
 the port C\ however, the piston has a deflector D which is in- 
 tended to deflect the incoming gas upward and reduce the loss to 
 a minimum. This deflector must be placed opposite the exhaust 
 port. 
 
 From the above we can readily understand, that when the 
 charge is being compressed in the cylinders on the up stroke of 
 the piston and before ignition takes place, a fresh charge is per- 
 mitted to enter the crank case and when ignition takes place the 
 gas expands, forcing the piston downward and nearing the bottom 
 of its stroke it uncovers first the exhaust port, permitting a fresh 
 charge to enter the cylinder, after which compression within the 
 cylinder again takes place, thus completing all four operations in 
 one revolution of the crank shaft or two strokes of the piston, 
 crank case intaking and cylinder compression on the up stroke, 
 expansion, exhaust and transfer of charge from crank case on the 
 down stroke. 
 
 The Four-cycle Type. The same operations occur in the four- 
 cycle type of motor; however, they require two complete revolu- 
 tions of the crank shaft or four piston strokes. This comprises 
 the following operations as mentioned below: (1) Admission of 
 charge to the cylinder, (2) compression of charge within the 
 cylinders, (3) ignition and expansion of charge, (4) exhausting 
 spent gases. 
 
 In four-c}^cle motors the inlet and exhaust of the charge is 
 entirely controlled by valves instead of the piston and ports in 
 the two-cycle motor. During the past few years numerous types 
 of valves have been used, such as the piston type, which may be 
 compared with a small piston opening and closing the ports at 
 the proper time, sliding sleeve, operated on the same principle, 
 and poppet valves which are opened by a cam mechanism. The 
 sleeve and piston valve motors have been experimented with for 
 pleasure car work; however, in commercial cars poppet valve 
 motors have been almost exclusively used in this country, and the 
 writer will confine his discussion to this type of four-cycle motor. 
 As mentioned above, the first stroke of a four-cycle motor is the 
 admission or intake stroke. 
 
THE MOTOR TRUCK ENGINE 
 
 9 
 
 The piston travels downward in the cylinder and at some 
 point in the wall of the combustion chamber an inlet valve is 
 located, which at the proper time opens and places the combus- 
 tion chamber in communication with the carburetor (see Fig. 7). 
 As this valve opens the piston has moved downward a short dis- 
 tance, and a vacuum has been formed with the cylinder which 
 creates a suction and permits the charge to enter. These valves 
 were formerly operated by this vacuum within the cylinder and 
 
 CYCLE OF OPERATIONS IN A FOUR CYCLE MOTOR. 
 
 FIG. 7. 
 Intake 
 Stroke. 
 
 FIG. 8. 
 
 Compression 
 
 Stroke. 
 
 FIG. 9. 
 Power 
 Stroke. 
 
 FIG. 10. 
 Exhaust 
 Stroke. 
 
 a light spring to close them when suction ceased. This type was 
 known as the automatic intake valve, but was discarded some 
 years ago, as it presented numerous disadvantages. At the pres- 
 ent time mechanically operated intake valves are used, which are 
 opened and closed by mechanical connection with the motor crank 
 shaft at the proper time. 
 
 This valve remains open until piston has passed the bottom 
 of its stroke, and shortly after the piston has started on its up 
 stroke it closes and remains closed during the completion of this 
 up stroke. During this up stroke the charge is compressed within 
 the combustion chamber (which is sometimes termed the com- 
 pression space) and prepared for ignition. So far the piston has 
 made two complete strokes, and the crank shaft one complete 
 revolution, while two operations have been completed within the 
 cylinders, this second operation being shown in Fig. 8. 
 
 Upon the completion of the compression stroke the gas is 
 ignited by introducing an electrical spark to occur within the 
 
10 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 combustion chamber. When the charge is ignited the pressure 
 rises to between four or five times what it was previously, caus- 
 ing the gases to expand and thus forcing the piston downward 
 and converting the heat of these gases into useful energy or 
 power. This stroke, known as the power stroke, is illustrated in 
 Fig. 9. 
 
 When the piston reaches the bottom of its stroke the exhaust 
 begins to open and the spent gases escape rapidly. This exhaus- 
 tion of spent gases continues all through the following return 
 stroke of the piston, the valve remaining open until the piston 
 has again moved downward a slight distance and then both valves 
 remain closed for a short period to create the vacuum which 
 causes the suction of gases from the carburetor on the intake 
 stroke, and permitting the motor to again resume its cycle of 
 operations. 
 
 The exhaust valves are always operated by mechanical con- 
 nection with the motor crank shaft, similar to the intake valve; 
 however, timing is different, as they must remain open longer 
 than the intake. In two-cycle motors the exhaust and transfer 
 ports must be placed opposite each other ; however, the valves of 
 the four-cycle type of motor may be placed in various positions, 
 as both valves are never open at the same time. Fig. 10 clearly 
 illustrates this point. The exhaust valve is shown and the piston 
 is traveling upward, while when the intake valve is open the 
 piston must travel downward. 
 
 In presenting these illustrations the writer has depicted valves 
 on both sides, so as to simplify the illustrations as much as pos- 
 sible. In the various motors the following valve arrangements 
 may be found: The valves may be on opposite sides of the cyl- 
 inder, which is called the T-head type while in others they are 
 located side by side, and known as the L-head type; they are 
 also located in the cylinder heads, and by combination of one 
 valve in the head and the other in the side; however, the first 
 three are the most popular types. 
 
 Advantages and Disadvantages of Both Types of Motors. In 
 
 the two-cycle motor we find that both the exhaust and transfer 
 ports are open together for certain periods, and it can readily be 
 understood that since we are performing the four operations in 
 two strokes of the piston, the time required for each operation is 
 limited. It was also stated that the exhaust port opened slightly 
 before the transfer port and that a fresh charge was admitted 
 
THE MOTOK TEUCK ENGINE 11 
 
 before the spent gases had entirely escaped. From this we can 
 assume that all the spent, gases do not escape and that there is a 
 possibility of part of the fresh charge escaping through the ex- 
 haust port, and the fresh charge becoming deluged with the spent 
 gases which do not entirely escape. In comparing the exhaust 
 and intake periods of both types of motors, we find that these 
 periods cover but approximately one-half the time in two-cycle 
 motors than in the four-cycle type. The combination of these 
 operations and the short periods naturally permit of less fuel 
 economy in the two-cycle motor. That considerable fuel is wasted 
 has been proven by exhaust gas analysis on numerous occasions. 
 
 In the four-cycle type we get a greater charge in the cylinders 
 due to the longer period, as one complete stroke of the piston is 
 required and this is maintained during the compression stroke 
 as both valves remain closed. This is of great importance in 
 high-speed motors, as even with the long periods intake becomes 
 very short when the higher engine speeds are reached and much 
 less gas enters the cylinders. Even in lower engine speeds it pre- 
 sents advantages. The cylinder also maintains its full volume 
 until after combustion occurs and the exhaust gases are forced 
 out of the cylinder by the return stroke of piston, during which 
 time the intake valve remains closed and no dilution of gases 
 occurs. Of course, some spent gases remain in the cylinders of a 
 four-cycle motor ; however, the quantity is much less and does not 
 have much effect on the next fresh charge. 
 
 There is also considerable power loss in two-cycle motors, due 
 to leaky pistons, crank case joints and cylinders and bearing 
 journals. This is of considerable importance, as the gas is partly 
 compressed in the crank case and can escape through the exhaust 
 port, should the rings leak or through the various joints, should 
 they not remain air tight. 
 
 In four-cycle motors power is lost through leaky pistons, and 
 valves; however, it is not as great and is of little importance as 
 the engine will continue to run and develop a small amount of 
 power. This is not the case with the two-cycle, as in the first 
 place the fresh charge is somewhat limited and, second, it can 
 escape before it reaches the cylinder, sometimes causing complete 
 stoppage of the engine. 
 
 Leaky valves can readily be reground at a small cost without 
 dismantling the engine, while to eliminate leaks in the two-cycle 
 means complete dismantling, which is an expensive item, as new 
 bearings must be provided in case they permit gas to escape, it 
 
12 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 being impossible to adjust them with shims and retain an air- 
 tight case. Crank case leaks are also of serious nature, as the 
 motor must be dismantled in order to replace the gaskets at the 
 various joints. Replacing rings is probably of equal expense in 
 both types. 
 
 The manufacturing cost is lower in the two-cycle type, while 
 it is also somewhat more simple, due to the absence of the valves 
 and their operating mechanism. As there are fewer parts and 
 the limitations of their proportions also means lower weight per 
 horse power for the two-cycle type, and it is also claimed that 
 they develop somewhat more power and have a better mechanical 
 balance. However, these features are obtained at considerable 
 expense in maintenance and it would seem that the logical com- 
 mercial car motor is one which provides the lowest maintenance 
 cost in proportion to the work done, which refers to the four- 
 cycle type. 
 
 The four-cycle motor also has its disadvantages, being more 
 complicated, more expensive to build and perhaps its weakest 
 point is the valves; however, they are readily accessible, and do 
 not mean much expense in regrinding or replacements. Leaky 
 inlet valves alone permit the diluting of the charge with spent 
 gases and indirectly reduce the power of the motor. The valve 
 operating mechanism of course is a source of complication and 
 expense and would be eliminated if this could be done without 
 too great a sacrifice in other directions. 
 
 It is also a well-known fact that carburetion is more difficult 
 in the two-cycle motor, which may be due to the fact that the 
 suction of the carburetor is more rapid and uneven in this type 
 than in the four-cycle type. 
 
 Two-cycle motors also require considerably more lubricating 
 oil and can not be lubricated by splash, owing to crank-case com- 
 pression. Forced lubrication from an outside source must be 
 used. While the two-cycle engine has been built for the past 
 twenty or thirty years, it has not been deemed worthy of the 
 serious attention of many engineers, and it has not yet reached 
 anything near the standardization and perfection of the four- 
 cycle engine. 
 
 Multi-cylinder Engines. For small moderate powers a single- 
 cylinder engine possesses the advantages of the simplest possible 
 construction, inexpensive to manufacture and maintain, and more 
 economical in the use of fuel. Along with its advantages, how- 
 ever, it possesses two inherent defects, particularly from the 
 
THE MOTOR TRUCK ENGINE 13 
 
 standpoint of its use in commercial cars, for which reason it is 
 new seldom employed. In discussing the cycle of operations it 
 was stated the power impulses were irregular, due to the fact that 
 a power stroke occurs every other stroke, or every fourth stroke 
 and that the gases which are compressed in the cylinders require 
 a certain portion of power to accomplish. 
 
 Therefore, in order to keep the engine running at a fairly 
 uniform speed against a nearly constant resistance it is necessary 
 to employ a heavy fly-wheel in which some of the energy liberated 
 on the power stroke can be stored, to be given out again during 
 the idle strokes. 
 
 A single-cylinder motor is sadly lacking in mechanical bal- 
 ance and the vibrations are great. These vibrations are due to 
 the reactions of the explosion and inertia forces. In a single- 
 cylinder motor the entire reciprocating mass (i.e., the piston with 
 its parts, the connecting rod, bearing and crank pin), is in a 
 single unit and the reaction of the inertia force of the parts pro- 
 duces a strong vibrating effect, while in multi-cylinder motors 
 the reciprocating masses can be divided into several units and so 
 arranged as to move in opposite directions, thereby neutralizing 
 the inertia effects. 
 
 The two-cylinder motors present some advantages over the 
 single-cylinder type. However, their use is also somewhat lim- 
 ited, and it is only a question of time until all commercial cars 
 will be equipped with four-cylinder motors. The two-cylinder 
 type presents an advantage over the single cylinder in that there 
 are two reciprocating masses, so arranged that one effects the 
 force of the other. However, perfect balance has not been reached 
 and vibrations are still noticeable to a considerable degree. 
 
 In the four-cylinder motors now extensively used in com- 
 mercial cars, the two inside reciprocating masses work together 
 and the two outside work together. However, they are so ar- 
 ranged that the two inner ones always set against the two outer 
 ones. Although they are equal in weight, they operate in oppo- 
 site directions. 
 
 The turning movement of a four-cylinder motor is also much 
 more uniform than that of a one or two-cylinder motor, hence 
 the torque reaction and vibration due to it are much smaller. 
 This four-cylinder type when properly constructed meets the re- 
 quirements of vibrationless running quite satisfactorily. 
 
 Types of Cylinders and their Parts. From what has been pre- 
 viously said of the piston strokes and crank shaft revolution it 
 
14 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 can readily be understood that the piston travels up and down 
 within the cylinder, while the crank shaft rotates in its bearings, 
 in order to impart a turning effort to the rear or driving wheels 
 of the vehicle through suitable power transmitting units. This 
 conversion of reciprocating into rotary motion will be depicted 
 below. 
 
 Advantages and Disadvantages of Different Types Discussed. 
 
 The construction of a gasoline engine is quite simple in its ele- 
 mentary form, being comprised of a cylinder, a piston provided 
 
 with rings operating within 
 the cylinder, a pair of valves 
 or ports which permit at the 
 proper time the entrance and 
 escape of the gases, a connect- 
 ing rod which connects the pis- 
 ton with the crank shaft, a case 
 which supports the crank shaft 
 and carries the valve operating 
 mechanism, this valve mechan- 
 ism being comprised of a shaft 
 with separate or integral cams, 
 suitable shaft bearings and a 
 train of gears driven from the 
 crank shaft; also a set of push 
 rods which act as intermediate 
 members between the valve 
 stems and the cams. 
 
 The cylinders are usually 
 castings made from close- 
 
 FIG. 11. Section of a Cylinder. 
 A Combination of Valve-in-Head 
 and L-Head Type. 
 
 grained iron provided with 
 either water jackets for water 
 cooling or fins, sometimes called 
 ribs for air cooling. They are open at one end, while the other 
 end is closed, forming the combustion chamber, in which the 
 valves are located. The walls of this cylinder are made very 
 smooth and are generally brought to a high polish by grinding, 
 so that the piston with its rings can slide freely within the cylin- 
 der. This cylinder, with its parts, is bolted to the crank case, 
 which carries the various other parts. Fig. 11 depicts a cylinder 
 in section showing its various parts. 
 
 The pistons of gasoline engines are of the trunk type, as illus- 
 
THE MOTOE TEUCK ENGINE 
 
 15 
 
 trated in Fig. 12, being somewhat longer than the diameter of 
 the cylinder. Near the center of the piston bosses are formed, 
 which receive the piston pin or gudion pin as it is sometimes 
 termed. Near the top three or four grooves are turned into the 
 piston which receive the eccentric piston rings, while near the 
 lower end oil grooves are turned for distributing and collecting 
 the surplus lubricating oil on the cylinder walls. These pistons 
 are made a trifle smaller in diameter than the cylinder to permit 
 of the expansion of the metal on the power stroke, while rings, 
 carried on the piston, permit of flexibility, so that the gases 
 cannot escape by the piston. 
 
 FIG. 12. Connecting- Rod, Piston Pin Crank Shaft, Flywheel and Main 
 Bearings of a Four Cylinder Engine. 
 
 The crank shaft is a horizontal steel shaft carried in journals, 
 or bearings, inside of the crank case, while offsets corresponding 
 with the number of cylinders are provided. These offsets are 
 termed the crank pins and carry the large end of the connecting 
 rod and its bearings; it is also provided with a taper or flanged 
 end to which the flywheel is attached by means of a key or nut 
 or bolts. 
 
 The connecting rod forms an intermediate link between the 
 piston and the crank shaft. It is usually made a drop forging, 
 
16 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 the small end carrying a bearing for the piston pin, while the 
 large end is divided and carries the crank pin bushing. 
 
 It was stated above that the piston travel was a reciprocating 
 motion while the crank shaft revolution was a rotary motion, and 
 that it was necessary to convert this reciprocating motion into 
 rotary motion, for the reason stated above. This conversion of 
 motion is performed by the connecting rod, as it is hinged to both 
 piston and crank shaft and this conversion of motion may be de- 
 picted as follows: 
 
 When the piston is at its upper point of travel in the cylinder 
 the cr*ank pin is standing vertical above the crank shaft, but as 
 the piston and connecting rod move downward under the influ- 
 ence of the expanding gases within the cylinders, the crank pin 
 is constrained and revolves downwardly, thus turning the crank 
 shaft. The crank pin passes through its horizontal position and 
 as the motion of the piston and connecting rod continues, finally 
 reaches a position vertically below the crank shaft, the piston at 
 this moment being at its lowest point and the crank shaft has 
 been revolved through one-half revolution. As the piston begins 
 to move upward upon its return stroke the crank shaft is again 
 constrained by the connecting rod to revolve and gradually ap- 
 proaches and passes its other horizontal position arid finally, 
 when the piston is all the way up, the crank pin has reached its 
 original vertical position again, having turned the crank pin 
 through one complete revolution. 
 
 Thus it can readily be understood that the upper end or piston 
 pin end of the connecting rod reciprocates in harmony with the 
 piston, while its lower end or crank pin end rotates in harmony 
 with the crank pin, converting the reciprocating motion of the 
 piston into rotary motion of the crank shaft. It should be re- 
 membered that in multi-cylinder engines the explosion force in 
 one cylinder will move the piston downward in the other cylinder 
 which is paired with it and is on the intake stroke. Thus in Fig. 
 12 the two end crank pins are vertical and while the right hand 
 one is being forced downward it carries the left-hand pin with it. 
 The left-hand cylinder being on the intake stroke, it also forces 
 the two lower crank pins upward, the corresponding cylinder of 
 one of these being on the compression stroke and the other on an 
 exhaust stroke. In this way the right-hand pin is revolved up- 
 ward when the lower pin on the compression stroke begins to 
 move downward on the next power stroke which, as stated in the 
 
THE MOTOR TRUCK ENGINE 17 
 
 previous article, follows compression. This operation is followed 
 by all crank pins on the various power strokes of the pistons. 
 
 In the single-cylinder motors this return motion is obtained 
 by the storage of energy in the flywheel on the power stroke, 
 which liberates itself on the idle strokes of the piston. This was 
 discussed under the heading of multi-cylinder engines. 
 
 The operation of the parts in two-cycle motors was depicted 
 previously, also the function of the valves in four-cycle motors, 
 the function of the valves being to permit the entrance and escape 
 of the gases from the cylinders at the proper time. These valves 
 are termed poppet valves and consist of a disc of metal with a 
 stem on one side, which closes a circular opening in the combus- 
 tion chamber, being held against the seat in the wall by a coiled 
 wire spring. The opening and closing of these valves is by a 
 force imparted from the cam shaft, which will be treated later. 
 
 Commercial car engines of the poppet-valve type are gener- 
 ally classified by the location of the valves within the cylinder, 
 as this point generally controls the entire construction of the 
 motor, as well as the various factors which enter into its design. 
 The various types of cylinders classified by their valve arrange- 
 ments are as follows : 
 
 T-Head. A type in which all valves are located in pockets at 
 opposite sides of the cylinders. 
 
 L-Head. A type in which all valves are located side by side 
 in one pocket, on either right or left side of the cylinder. 
 
 Valve in Head. A type in which all valves are located in the 
 cylinder head, placed vertically or at an angle. 
 
 There are also several other types which are combinations of 
 those depicted above, having one valve in the head and the other 
 in a pocket at the side, or both valves in a pocket at the side, one 
 being located above the other. 
 
 The first and second types, namely the T-head and the L-head, 
 are by far the most popular type used in commercial cars. How- 
 ever, quite a few of the others may also be found. The first 
 three types possess an advantage in that all working parts may 
 be inclosed and thoroughly protected from grit. They also pre- 
 sent a neater appearance in that it is a simple matter to keep 
 them clean, as all parts are lubricated internally. 
 
 The writer is presenting several illustrations which depict 
 these various types taken from illustrations furnished by the 
 various makers of these engines. 
 3 
 
18 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 Fig. 13 depicts the conventional type of T-head cylinder in 
 which all the intake valves are located on the right side and all 
 
 the exhaust valves on the left 
 side, the valves being" inserted 
 through openings in the com- 
 bustion chamber, which are 
 covered by valve port plugs 
 that carry the spark plugs. 
 
 Fig. 14 depicts the conven- 
 tional type of L-head cylinder 
 in which all intake and exhaust 
 valves are located on the left 
 side, the intake and exhaust 
 valve of each cylinder being 
 located side by side in a pocket. 
 The valves have conical seats, 
 as those depicted in Fig. 13, 
 and are also inserted through 
 FIG. 13. Sectional View of T-Head openings in the combustion 
 
 chamber, which are closed by 
 the valve port plugs. The 
 
 Cylinder. 
 
 plugs which cover the intake 
 valve openings carry the spark 
 plugs, while the exhaust port 
 plugs carry the relief or prim- 
 ing cups. In this motor the 
 valve springs are of conical 
 shape, the object of this being 
 to obtain a more gradual seat- 
 ing of the valve. The valve 
 stems and operating parts are 
 also enclosed; however, two 
 aluminum plates are used, each 
 covering four valve stems. 
 They are retained by a wing 
 nut and stud, which may be 
 quickly removed. 
 
 Fig. 15 depicts a valve in 
 the head-type cylinder in which 
 the valves are placed vertical. The valve stems only pass through 
 the cylinder and for this reason the cylinder is divided in two 
 
 FIG. 14. 
 
 Sectional View of L-IIead 
 Cylinder. 
 
THE MOTOR TRUCK ENGINE 
 
 19 
 
 parts at the top of the compression space. Valve guides are used 
 to provide a bearing for the valve stems, and coil wire springs 
 keep the valves closed. This 
 construction presents an ad- 
 vantage in that the entire 
 compression space may be ma- 
 chined to a polished surface, 
 thus reducing the tendency 
 for carbon to collect in the 
 combustion chamber and di- 
 viding the cylinder at this 
 point also facilitates the re- 
 moval of carbon when it does 
 form. If this type of cylin- 
 der were cast in one piece it 
 would be necessary to remove 
 it from the engine in order to 
 grind the valves, unless they 
 were mounted in cages which 
 could be removed. 
 
 Fig. 11 depicts one type of 
 the combination of types and 
 is the only arrangement re- 
 sorted to by American mak- 
 ers, the other type of placing 
 one valve over the other has 
 never been used on commer- 
 cial car motors to the writer's 
 knowledge, the combination 
 in this type being identical 
 with the construction of the 
 other types from which they were derived, one valve being located 
 in a p'ocket and operated directly, while the other is located in the 
 head and is carried in a cage in the cylinder head and operated 
 through a rocker arm. 
 
 During the past year there has been a tendency to divide 
 L-head cylinders of the motor used in light delivery wagons, so 
 that part of the crank case could be cast integral with the cylin- 
 ders. This construction, of course, presents advantages in the 
 removal of carbon, valve grinding, finishing of the combustion 
 space, as well as reducing the cost of manufacture. It remains, 
 
 FIG. 15. Sectional view of Valve- 
 in-Head Cylinder. 
 
20 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 however, to be seen just what popularity this construction will 
 gain in the heavier types of motors. 
 
 There are various ways of grouping cylinders, as they may 
 either be cast single, in pairs or en bloc. Where they are cast 
 single the motor becomes of considerable length and, of course, 
 requires a much longer hood; this additional space when added 
 to the loading compartment would naturally be of considerable 
 advantage. Casting them in pairs shortens the motor somewhat. 
 However, the ideal construction is obtained when the cylinders 
 are cast en bloc, which permits of the shortest possible hood 
 length. It also presents an advantage in the shorter length of the 
 vital parts such as the crank and cam shaft, crank case, etc., as 
 the space wasted can be put to good advantage by the increasing 
 of the main bearings and the shortening of the unsupported parts 
 of these shafts. 
 
 This method of cylinder grouping can be applied to any type 
 of motor, or valve arrangement, and is not dependent upon any 
 one construction. En bloc cylinder construction does present a 
 very simple and neat motor, especially when all parts are properly 
 enclosed. 
 
 The Valve Operating Mechanism and the Crank Case. Hav- 
 ing described the functions of the valves in their respective cyl- 
 inders, we can next consider how their operation is accomplished, 
 at the proper time, by mechanical connection with the crankshaft. 
 
 Functions of the Cams and Cam Shaft. This is accomplished 
 by cams which are attached to, or formed integral with, a shaft 
 termed the "camshaft," which in turn is driven through a gear, 
 which meshes with an idler gear, or with the crankshaft gear. 
 When an idler or intermediate gear is used it is so placed that it 
 will mesh with both the crankshaft and camshaft gears. It is 
 only used when the latter gears cannot be meshed directly, due to 
 the difference in centers between cylinders and valves and the two 
 shafts. 
 
 The camshaft is so designed that the rise of the cam is brought 
 into operation at the proper time, causing the valve to be raised 
 from its seat and to permit a charge to enter or escape from the 
 cylinder. This cam only causes the valve to raise from its seat; 
 in other words, causes the valve to open, while the valve spring 
 performs the function of closing it and holding it down on its 
 seat until the cam again opens the valve. In the discussion of the 
 two and four-cycle motors it was pointed out that one valve 
 opens during each revolution of the crankshaft, the valves alter- 
 
THE MOTOR TRUCK ENGINE 21 
 
 nating, first one and then the other. From this it can readily be 
 understood that the camshaft must revolve at one-half of the 
 crankshaft speed, thus necessitating a two to one reduction in the 
 timing gears. 
 
 In this case we also have to convert a rotary motion into a 
 reciprocating motion. However, as no permanent connection is 
 made with the camshaft, this becomes a simple matter by provid- 
 ing what is termed the pushrod, one end of which communicates 
 with the valve stem and other end rests on the cam. It is pro- 
 vided with a suitable bearing so that its relation with the cam- 
 shaft can always be maintained. 
 
 These pushrod^ may either have the bearing or guide in the 
 crank case or in the base of the cylinders. When the valve stems 
 are enclosed it is more advantageous to place them in the cyl- 
 inders, as it somewhat simplifies the machining operations of the 
 case and also the assembling of the motor. These pushrods are 
 always provided with adjusting screws, so that as little lost motion 
 as is practical may be present between the valve stem and the 
 cam. This feature can also be maintained through these screws 
 which are locked in position by lock washers and nuts. 
 
 All T-head motors require two camshafts, while the balance 
 of the types illustrated require but one shaft, as all valves can be 
 operated from one side of the motor. Two camshafts could be 
 used in the other types, excepting the L-head, but this of course 
 would add complications in the motor. The train of gears for 
 operating the valve and the accessories is dependent upon the 
 number of shafts and the general distribution of the accessories. 
 They are generally provided with helical teeth and located in a 
 housing at the forward end of the crank case. They must be com- 
 pletely enclosed so that they may be effectively lubricated and 
 protected from dust. This housing is generally built into the 
 case and provided with a cover plate. 
 
 The Crank Case. The crank case, as mentioned in the pre- 
 vious installment, serves as the main structural part of the motor, 
 carrying the cylinders, crankshaft, camshaft and accessories, and 
 is in turn supported in the vehicle frame. It also forms a hous- 
 ing for these important parts, protecting them against dust and 
 mud, and also performs important functions in connection with 
 the lubrication of the motor. The crank case generally forms 
 either a cylindrical or box-shaped housing of sufficient size to 
 enable the crank pins with their respective connecting rods to 
 
22 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 rotate freely within it and sufficiently long to accommodate all of 
 the cylinders of the motor, which are bolted over the opening in 
 the top of the case. 
 
 The general design of this case depends, of course, upon the 
 number of cylinders, the valve location and the size of the crank- 
 shaft and its bearings. 
 
 There are various methods of mounting the motor in the 
 vehicle frame, each having its advantages and disadvantages. 
 The case is generally provided with four arms, which may either 
 be cast integral or bolted to it, when main frame mounting is re- 
 sorted to, while for sub-frame mounting they are always cast 
 integral. 
 
 Lately there has been quite a tendency toward the use of a 
 three-point support for the motor so as to eliminate stresses in 
 the case, due to frame weaving from road irregularities. This 
 type of motor support may either be incorporated in the motor, 
 by using a separate arm pivoting around the crankshaft center at 
 either the front or rear end, when main frame mounting is re- 
 sorted to and by incorporating this support at either the front or 
 rear end of the sub-frame when the latter mounting is used. 
 
 Crank cases may either be formed in one piece with a separate 
 oil reservoir or in two pieces divided on the horizontal center of 
 the crankshaft. They may either be cast iron or aluminum and 
 in several instances manganese bronze has been used. Aluminum 
 is the most popular, provided with separate steel supporting 
 arms which are bolted to the case, owing to the heavy vibrations 
 due to the solid tires. 
 
 Unit Power Plants. Quite a few of the commercial vehicles 
 use the unit pow r er plant in which the gear box or transmission is 
 bolted directly to a housing cast integral with the case and sur- 
 rounding the flywheel, or by separate arms which are bolted to 
 the rear motor arms. However this method is very rarely re- 
 sorted to in the heavier types owing to the large size of the trans- 
 mission, its weight and the necessity of providing a separate jack- 
 shaft for chain driven vehicles. 
 
 Like all other units of the commercial car, there are various 
 designs which have been worked out and giving excellent results, 
 and the writer presents illustrations of the types conforming to 
 the general outline of the motors referred to. 
 
 The writer will not endeavor to describe the various methods 
 of mounting the engine in the vehicle frame, as this can be done 
 
THE MOTOR TRUCK ENGINE 
 
 23 
 
 more clearly by devoting a chapter to this feature which will 
 cover all of the present methods pertaining to all units mounted 
 in the frame. 
 
 COYER 
 PLATE 
 
 BEARIN 
 
 CAM SHAF 
 
 CRANK SHAFT ^ 
 FIG. 16. Showing Valve Mechanism of L-IIead Motor. 
 
 Fig. 16 shows the valve operating mechanism used on a promi- 
 nent L-head commercial car motor, illustrating how the valves 
 are located side by side. The European type of valve, with con- 
 ical seat and the most popular method of enclosing the valves to 
 protect them from dust and foreign matter, are shown. The 
 pushrod guides are pressed into the cylinder and can readily be 
 removed from the bottom of the same. When the cylinder is re- 
 moved from the crank case the entire valve mechanism, excepting 
 the cams and their shaft, is removed with the cylinder, a note- 
 worthy feature when the overhauling of an engine is considered. 
 The pushrod is of the mushroom type and the outline of the cam 
 is formed of curves, to further assist in obtaining a quieter valve 
 action. The conventional type of pushrod adjustment incorpo- 
 
24 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 FIG. 17. Showing the 
 Method of Operating 
 Valve when Located in 
 Cylinder Head. 
 
 rating a hardened steel screw and lock nut is used. This view 
 also shows the large bearing provided for the cam shaft so that 
 it may be removed through the forward end of the case. Helical 
 
 teeth are used on the timing 
 gears and the end thrust is 
 taken by a hardened steel 
 pin supported by a spring 
 which transmits this thrust 
 to hardened steel washer on 
 the timing gear housing 
 cover. 
 
 Fig. 17 illustrates the 
 method of operating the 
 valves when they are located 
 side by side in the cylinder 
 head. The pushrods are 
 similar to those previously 
 described above, however, 
 the adjustment is omitted 
 here and incorporated with 
 the rocker arm mounted on 
 
 top of the cylinder. These rocker arms pivot on a 
 shaft and their opposite ends bear against the valve 
 stems. The operating rod placed between the push- 
 rod and the adjustment in the rocker arm has a ball- 
 shaped end to reduce wear at this point. 
 
 Fig. 18 illustrates the overhead type of valve me- 
 chanism for valve in the head cylinders with valves 
 set at an angle on opposite sides and operated through 
 one camshaft located on the cylinder heads. It will 
 be noticed that a very light spring is used for the in- 
 take valve, while a very stiff spring is used for the 
 exhaust valve. The object being to make the intake 
 valve partly automatic, owing to the fact that but 
 one rocker arm is used to operate both valves. The 
 rocker arm of course replaces the pushrods and the 
 adjustment is incorporated in the ends of the arms. 
 The rocker arm has a roller bearing 'against the cam, and these 
 two parts are kept in contact by a large spiral spring. The cam- 
 shaft bearings are divided, but require considerable attention, as 
 a wick feed is resorted to for supplying lubricant. The cam, 
 
THE MOTOR TRUCK ENGINE 
 
 25 
 
 roller and other parts are exposed so that grit and foreign matter 
 can reach them, and it is a contraction very hard to lubricate 
 due to the intense heat on the cylinder heads. 
 
 FIG. 18. Overhead Type of Valve Mechanism. Valves set at an Angle. 
 
 The combination type of valve arrangement of course em- 
 bodies the features of those just described. Fig. 16 can be ap- 
 plied to the valve in the pocket, while Fig. 17 would apply to the 
 valve in the head or in the pocket when these are placed one above 
 the other. 
 
 Various methods are resorted to in fastening the pushrod 
 guides into the cylinders or case. They may either be pressed in 
 position, held down in pairs by clamps or bolted down. 
 
26 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 These various constructions may be applied to most any valve 
 location. The principal change would come in the crank case, 
 which is dependent upon the number of camshafts that are neces- 
 sary to operate the valves. Enclosing the valve stems and push- 
 rods is now quite popular. 
 
 Fig. 19 illustrates a bottom view of a T-head crank case in 
 which the two camshafts with the respective parts are clearly 
 shown. This view also shows a three-bearing crankshaft with 
 
 CAM 
 SHAFT 
 
 CAM 
 
 SHAFT 
 
 OIL PUMP 
 
 FIG. 19. Bottom View of a T-Head Crank Case, Showing two Cam Shafts. 
 
 the connecting rods fastened in position on the shaft and in the 
 piston. The case is divided and all bearings are held in position 
 by separate caps, while the cams are of considerable width, as the 
 exhaust camshaft can be moved longitudinally so as to provide a 
 compression release for cranking the motor. This is accom- 
 plished through the use of stepped exhaust cams which open the 
 exhaust valve part way during a portion of the compression 
 stroke while cranking the motor. The water pump is located at 
 the front end of the motor and is driven through separate gears 
 meshing with camshaft gears. The oil pump is located on the 
 rear motor arm and is driven through a ratchet and link connec- 
 tion with a valve pushrod. 
 
THE MOTOR TRUCK ENGINE 
 
 27 
 
 Fig. 20 illustrates a bottom view of a crank case for the L-head 
 motor. It shows the camshaft and crankshaft in position, with 
 the connecting rods mounted on the crank pins. But one cam- 
 
 FIG. 20. Bottom of Crank Case of L-Head Motor. 
 
 shaft is used, and is driven through helical gears, the accessories 
 are mounted on opposite sides and also driven through helical 
 gears. The crankshaft is of the five-bearing type, while the case 
 
 FIG. 21. Bottom View of Crank Case having Separate Compartment 
 
 for Oil. 
 
 is divided on the horizontal center of the crankshaft, all the im- 
 portant parts being carried in this upper half of the case, the 
 
28 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 lower half serving only as a dust protection, oil splash basin and 
 reservoir. 
 
 Fig. 21 illustrates the bottom view of a prominent valve in 
 the head motor, with a three-bearing crankshaft and one cam- 
 shaft for operating the valves. This crank case differs somewhat 
 from the above in that it is cast in one piece with a separate oil 
 reservoir bolted to it. The timing gears are carried in a housing 
 at the front end of the case, enclosed by a .steel cover plate. The 
 magneto is driven from the timing gear housing through flexible 
 couplings in the conventional way, while the pump is driven 
 through spiral gears from the camshaft. 
 
 TIMING 6EAR 
 CAM 
 
 ROLLER TYPE 
 PUSH ROD 
 
 ILtYLINOER 
 
 FLY 
 
 WHEEL 
 
 CRANK 
 SHAFT 
 
 CRANK CASE 
 OIL RESERVOIR 
 OIL FUMF 
 
 FIG. 22. Sectional View of Two Cylinder Opposed Motor. 
 
 Fig. 22 shows a sectional view of a two-cylinder opposed 
 motor. This type of motor is mostly used on the light commer- 
 cial vehicles, and the case is generally made from cast iron. This 
 case is cast in one piece with circular openings on the ends, 
 through which the crankshaft is inserted. Plates are mounted 
 in these openings and bolted to the case which carries the crank- 
 shaft bearings. A large cover plate is used, which carries the 
 camshaft, gears and pushrods. The water pump is driven by the 
 camshaft bevel gears, while the oil pump is driven through an 
 idler gear from the crankshaft. 
 
THE MOTOR TRUCK ENGINE 29 
 
 In some of the two-cylinder motors in use at present the case 
 is divided on the vertical center of the crankshaft and each half 
 is cast integral with a cylinder, while the pushrods and cam- 
 shafts are also located in the case instead of on the cover plate. 
 
 In the two-cylinder opposed type of motor the distance be- 
 tween the crankshaft and the camshaft is generally greater than 
 the distance between the valve and the cylinder centers. This is 
 due to the fact that in this type of motor the camshaft is located 
 at right angles to the cylinder axis, while in the vertical motors 
 it generally makes an angle of 45 to 60 degrees with the cylinder 
 axis. The former case makes it necessary to either place the valve 
 chamber farther from the cylinder axis, thereby increasing the 
 length of the valve passage and consequently the compression 
 space wall area, which is not good practice, or to offset the valves 
 from the camshaft center and to provide the pushrods with an 
 overhanging striker. In Fig. 22 the pushrods are set at an angle 
 to overcome this point, which in this case is easily accomplished, 
 as the valves are carried in the head of the cylinder and operated 
 through a rocker arm. 
 
 Motor Lubrication. Developments in the line of motor lubri- 
 cation as a matter of course follow on the heels of progress in the 
 art of motor design and construction, for the increase of efficiency 
 which marks the refinement of the motor and its various parts 
 can only be reached if the refinements are paralleled by those 
 essentials which permits the units to perform their required duty. 
 In commercial car motors, the two features, outside of actual 
 mechanical construction and the essential details of ignition and 
 carburetion, which help to the attainment of the highest results 
 with the least expenditure are the cooling and lubricating systems. 
 
 The functions of the cooling system are different from those 
 of the lubricating system and will be considered in a separate 
 article following the present one. 
 
 All parts which rub together under pressure, such as the pis- 
 tons moving upward and downward within the cylinders, the 
 connecting rods on the piston and crank pins, the crank shaft in 
 its bearings and all reciprocating and revolving parts must be 
 efficiently lubricated. Whenever two surfaces are in contact and 
 one or other is free to move when a force is applied, there is pres- 
 ent a certain amount of friction, which develops instantly when 
 these surfaces are not properly lubricated. 
 
 Friction is a resistance to motion of two bodies in contact and 
 
30 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 is dependent upon certain laws. It will vary in proportion to the 
 pressure applied when the rubbing velocity remains constant. 
 All wearing surfaces, no matter how carefully prepared, are 
 known to consist of minute lumps and hollows. This is true, even 
 of the smoothest surfaces that can be made, although, of course, 
 the height of the depressions and hollows varies with different 
 materials and the finish. The condition of bearing surfaces in 
 an exaggerated degree may be likened to the nap of woolen cloth 
 and the pile of velvet. 
 
 When the two surfaces are held in contact by an appreciable 
 force these minute parts of the surfaces interlock and resist rela- 
 tive motion. This force is called the force of friction. This fact 
 can easily be demonstrated by placing a book upon a table or 
 smooth board and moving it across the latter, comparing the dif- 
 ference in energy required to move the book across the surface 
 by placing a weight upon it. If this experiment were conducted 
 with two metallic objects and the surfaces were lubricated, con- 
 siderable less energy would be required. 
 
 Friction in reality is heat, which in a short period of time will 
 reach an intense degree and in time the surfaces will be broken 
 down and if the rubbing continues they will be completely de- 
 stroyed. The action and effect of this friction upon two surfaces 
 not properly lubricated may be explained as follows: At first 
 small particles of metal are torn from the surfaces and these cut 
 and abrade the bearing. As the surfaces continue to roughen, 
 the friction increases enormously until it reaches the fusing point 
 of the metal, when the two surfaces will weld into one solid mass. 
 
 A lubricant should possess certain qualities, since its object is 
 to flow between the surface of a bearing, reduce its friction and 
 to radiate a certain amount of heat generated by the bearing. 
 These properties are termed adhesion, cohesion or viscosity, a 
 high flash point and a comparatively low cold test point. It 
 should have considerable adhesion so that the molecules of oil 
 will cling together, considerable cohesion or viscosity, as all bear- 
 ings are subjected to a pressure, created by the force acting upon 
 them and the effect of this pressure is a tendency to separate 
 these molecules forcing sufficient lubricant out of the bearing to 
 allow the metals to come into contact. 
 
 The advantage of a high flash point is that the oil will not 
 give off an inflammable vapor at ordinary temperature, while it 
 should have a low cold test point, so that it will stay in fluid state 
 when cold temperature are encountered. The high flash point is 
 
THE MOTOR TRUCK ENGINE 31 
 
 very desirable; for in lubricating the cylinders, the oil comes in 
 contact with the walls of the combustion chamber and the heat in 
 the cylinder on the power stroke. If the temperature is raised 
 sufficiently to vaporize the oil, the viscosity is entirely overcome 
 and the various residue products of the lubricant are deposited 
 on the walls of the combustion chamber. This residue product is 
 termed carbon and in time will harden, become incandescent and 
 fire the charge prematurely, causing excessive strains on the 
 various parts of the motor. The final result is that the motor will 
 begin to pound, overheat very easily, the valves will pit and the 
 spark plugs become fouled. 
 
 The advantage of a low cold test point is that it will flow 
 freely in cold weather, preventing the oil leads and pump from 
 clogging up. 
 
 There are various methods of lubricating the working parts 
 of commercial car engines, and it is a difficult matter to classify 
 them. We may distinguish, however, between the following: 
 Plain splash; splash from constant level troughs with pump cir- 
 culation; part force feed and part splash; force feed without 
 splash ; either from an external source or built into the motor. 
 
 The simple splash system was much used on the earlier models 
 of commercial cars. The crank case contained a supply of oil 
 into which the connecting rods dipped at each revolution of the 
 crank pin, thereby splashing oil over the interior parts. As the 
 oil worked out through the bearings or past the pistons, the oil 
 level in the crank case fell and the splash became weaker. When 
 the operator considered that the oil level had become too low, he 
 would replenish the supply by either pouring oil into the crank 
 case through a filling hole or transferring it from a supply tank 
 to the crank chamber by means of a hand pump provided for the 
 purpose. 
 
 The disadvantages of this system are apparent. The oil level 
 varied constantly and so did the rate of supply to the bearing 
 surfaces. When the crank case was replenished, the oil level was 
 raised considerably and the supply to cylinder walls was generally 
 excessive and the motor, in consequence, would pour dense smoke 
 out through the muffler. In order to overcome this feature, some 
 makers placed baffle plates between the cylinder and the crank 
 case with an opening in the form of a rectangular slot for the 
 connecting rod to pass through. Moreover this system required 
 frequent attention from the operator, and if the latter were care- 
 less, the motor could easily be injured through the lack of oil. 
 
32 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 Through the deficiencies mentioned above, lubrication by 
 multiple feed mechanical oilers came into vogue. These oilers 
 consisted of an oil reservoir carrying a series of plunger pumps, 
 which forced the oil through individual leads to each part re- 
 quiring lubrication. Each lead had its own pump, so that the oil 
 was forced to each bearing in proportion to the speed of the 
 motor. While this system was effective, its complications were 
 objectionable. It was difficult to obtain a positive drive and the 
 maze of oil tubes running from the oiler to the engine, rendered 
 access to the latter difficult and presented a frail and non-mechan- 
 ical appearance. It was also difficult to prevent leaks at the 
 various connections and considerable oil was wasted. 
 
 Following this the pump circulating systems were introduced, 
 as it was felt that a simpler system was needed and one that was 
 at the same time thoroughly automatic. The gear and plunger 
 types of oil pumps are most popular ; however in some cases vane 
 pumps are also used. 
 
 The gear pump consists of a casing in which fit snugly two 
 spur gears, one driven by means of its shaft and gears from the 
 cam shaft and the other by meshing with the former. The oil 
 enters the housing on the side on which the meshing teeth separate 
 and fills the spaces between adjacent teeth and the wall of the 
 housing. It is thus carried around to the opposite side of the 
 housing and leaves through an opening there. 
 
 Plunger pumps are generally placed inside the crank case and 
 driven by eccentrics from the cam shaft. They consist of a brass 
 barrel set in the case and carrying a plunger, which is held in 
 
 contact with the eccentric 
 by a spring. .Below the 
 spring a ball valve is 
 placed. As the plunger 
 moves upward, the lower 
 end of the barrel increases 
 in volume and oil enters 
 through the ball valve. 
 When the plunger is next 
 moved down by the eccen- 
 
 FIG. 23. Exterior of a Mechanical Oiler. trie, the ball valve closes 
 
 and oil is forced up 
 
 through and out another ball valve, which remains closed on the 
 upward stroke of the plunger. 
 
THE MOTOE TKUCK ENGINE 
 
 33 
 
 In what follows the writer will attempt to describe and illus- 
 trate the most popular systems in use at present, among which 
 both the gear and plunger types of pumps will be found. 
 
 Fig. 23 shows a mechanical oiler which operates in the follow- 
 ing manner. A series of double plunger valveless pumps are 
 driven by belt from a cross shaft which is driven by the engine. 
 One set of plunger pumps lift oil from the reservoir and dis- 
 charge it from the nozzles in the sight feed compartment, the 
 amount of oil discharged being regulated by the adjusting screws 
 A, directly in front of the sight feed. The other set of plungers 
 take oil from the sight feed compartments and deliver it to the 
 various parts of the engine through the oil lead connected with 
 the pump outlet B. The plungers work alternately and each acts 
 on a check valve for the other. 
 
 FIG. 24. Recirculating 1 Splash System of Lubrication. 
 
 Fig. 24 illustrates a circulating splash system which has been 
 used for a number of years on a prominent motor. Two plunger 
 pumps are located in the lower half of the case and driven by 
 eccentric from the cam shaft. One pump supplies oil to the 
 timing gear compartment, and from these points it overflows to 
 the splash troughs cast integral with the case. 
 
 The connecting rods are provided with dippers which are 
 hollow and permit a certain amount of oil to reach the connect- 
 ing rod bearings during each revolution of the crank pin. They 
 also splash oil over the interior parts of the motor, the crank 
 and cam shaft bearing housings being provided with pockets 
 which store the oil and feed it to the bearings as it is needed. 
 4 
 
34 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 Each connecting rod has a separate trough into which it dips, 
 and the two forward ones are separated from the rear by a high 
 
 partition, so that a positive 
 oil level can be maintained 
 for all conditions, when 
 traveling up or down 
 grade. 
 
 Fig. 25 shows another 
 constant level splash sys- 
 tem of the recirculating 
 type. The operation of the 
 system is similar to the one 
 explained above, oil being 
 supplied to the stationary 
 troughs by a gear pump. 
 Scoops on the connecting 
 rods dip into these troughs 
 
 FIG. 25. Base Removed on Constant- and cause the oil to s P lash 
 Level Splash Lubricated Motor. onto the pistons and into 
 
 the small reservoirs which 
 
 lead to the various bearings. The surplus oil drains back to the 
 main reservoir, when it is thoroughly strained and again recir- 
 culated. 
 
 Fig. 26 illustrates a gravity-feed system using a gear pump 
 for supplying oil to the gravity tank from the reservoir in the 
 lower half of the case. This gravity tank is placed at the top 
 level of the cylinders and has an oil lead of large diameter to 
 each of the main bearings and the timing-gear compartment. 
 The delivery pipe and leads are provided with strainers, so that 
 the oil is thoroughly strained before being recirculated. The 
 crank shaft journals and short arms are drilled through, so that 
 the oil can pass from the main bearings to the connecting rods, 
 centrifugal force being relied on to carry this oil to the connect- 
 ing rods. Part of this oil works through these bearings and 
 creates a spray, as in the force-feed system. This spray lubricates 
 all other moving parts. It will be noted that the shape of the oil 
 tank is such that when the car is moving up or down grade all 
 bearings will receive an equal amount of oil. An oil gage on the 
 dash shows the amount of oil in the tank, indicating that the 
 pump is doing its work. 
 
 Fig. 27 illustrates a sectional view of a full force feed system 
 of lubrication which is built into the motor. Oil is carried in a 
 
THE MOTOR TRUCK ENGINE 
 
 35 
 
 reservoir bolted to the crank case and is circulated by a gear 
 pump mounted at the rear end of the case driven from the cam 
 shaft. The pump forces oil up through a pipe over the main 
 bearings and is provided with a pressure relief valve. This dis- 
 
 HAN Or OH. PUMP 
 
 FIG. 26 Combination Pump and Gravity System. 
 
 tributing pipe has branches which communicate with the main 
 bearings and the timing gears. From the main bearings the oil 
 is forced through a hollow crank shaft to the connecting rod 
 bearings. These connecting rods have tubes inserted in them so 
 that the oil can be forced up to the piston pin bearings. Cam 
 shaft bearings are lubricated by means of passages connected with 
 the system. A certain portion of the oil works out from the con- 
 necting rod bearings, is thrown off as the crank shaft revolves 
 
36 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 and forms a fine spray which lubricates the cylinders, pistons and 
 interior parts of the motor. An indicator which shows at all 
 times the level of oil in the reservoir is placed adjoining the com- 
 bination breather and filling tube. The oil pump and its strainers 
 are removable from the lower half of the crank case without dis- 
 
 FIG. 27. Full Force Feed Lubricating System. 
 
 turbing other parts. The pressure relief valve permits a certain 
 oil pressure on the bearings. Should the pressure exceed this 
 predetermined amount the relief valve will open, permitting the 
 excess oil to return to the reservoir. Oil which overflows and 
 accumulates in the case flows into a trough into which the con- 
 necting rods dip. This trough has holes on one side which allow 
 the oil to drain back to the reservoir beneath so that a constant 
 level of oil is maintained. 
 
 Fig. 28 illustrates the Mack oiling system which is a com- 
 bination of the gravity and force feed type. Oil is pumped from 
 the reservoir at the bottom of the crank to a tank cast integral 
 with the front pair of cylinders. This tank is provided with a 
 filter and an overlow which leads to the timing gear housing. 
 This tank serves two functions: first, to heat the oil while the 
 
38 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 engine is cold so that the oil will flow freely and second, to cool 
 the oil when the engine is working hardest, as the oil may reach 
 a temperature of 390 degrees Fahrenheit, while the cooling sys- 
 tem seldom reaches a temperature higher than 190 degrees 
 Fahrenheit. From the tank the oil flows to a main header which 
 supplies oil to the main bearings and through a second header 
 which supplies oil to the troughs into which the connecting rods 
 dip. A pressure gauge is used to indicate the oil pressure and 
 the pump is provided with a strainer to filter the oil before it is 
 recirculated. 
 
 The constant level splash and force feed systems are the most 
 popular, and as positive driven pumps are resorted to, to feed the 
 oil, the general tendency is to provide oil leads of a large diam- 
 eter and to reduce the number of bends to a minimum. Whenever 
 bends are necessary they should be made as large as possible to 
 reduce the obstructions and resistance. 
 
 From the above it can readily be understood that the writer 
 considers the constant level splash recirculating system the sim- 
 plest in use at present. Its operation is mechanical and the at- 
 tention required is reduced to a minimum, while at the same time 
 it is quite economical on oil. 
 
 The advantages of the force feed system are that the oil may 
 be forced to the bearings under separate pressure, reducing the 
 danger of the oil being forced out by the bearing pressure. It is 
 generally agreed that with force-feed the specific pressure on the 
 bearing can be increased and that the bearing will last longer, 
 while on the other hand the writer finds that this system is more 
 expensive to install and less economical of oil. It would appear 
 to be better adapted to commercial car engines which operate at 
 or near their full load for a considerable length of time. 
 
 In the gravity feed system the oil leads must be carried on the 
 outside of the motor, which presents some complications, as they 
 will require attention at intervals. The economy is possibly on a 
 par with the constant level splash system. Mechanical oilers are 
 very rarely used on the types of commercial cars, being prac- 
 tically obsolete. 
 
CHAPTEK III 
 
 THE MOTOR COOLING SYSTEM 
 
 CONTINUING from the previous chapter we can next investi- 
 gate the cooling system, considering first the office of the cooling 
 system. This system must cool the cylinder walls to such an ex- 
 tent as to permit of the proper lubrication and to prevent the 
 carbonization of the lubricating oil. Preignition will also occur 
 if the metal is permitted to heat to a red heat, causing the gas to 
 ignite on the compression stroke. It is the general impression 
 that the office of the cooling system is to abstract the heat from 
 the gases within the cylinders, this heat having been generated by 
 the explosion. This is not the case, for, as a matter of fact, the 
 duty of the cooling medium is to keep the cylinder walls cool, the 
 heat of the gases being converted into useful energy. 
 
 The Direct or Air System. There are two general types of 
 cooling systems, the direct or air system and the indirect or a 
 system using a cooling medium such as water or oil. The term 
 direct is applied to the air system, as there is no intermediate 
 transfer of heat from the cylinder walls to the radiating surfaces 
 by means of a cooling liquid. Air cooling is generally effected 
 by cooling ribs or fins as they are sometimes called, cast integral 
 with the cylinder walls and head. Some mechanical method, such 
 as mounting a fan at front of the motor, or combining it with the 
 fly wheel, is generally resorted too for inducing air circulation. 
 Fig. 29 illustrates a typical air cooling system. This type of 
 cooling system is most popular on the low-priced vehicles using 
 two, three and four-cylinder motors. It may be used on either 
 two or four-cycle motors. 
 
 The Indirect System Water or Oil. The indirect cooling 
 system as mentioned above involves the circulation of a liquid 
 such as water or oil, to absorb the heat and deliver same to a 
 current of air which is passed over the surface of the radiator 
 within which the liquid in its heated state is circulated. At 
 present water is used as the medium in all indirect systems. Oil 
 was used in some cases, but it presented serious disadvantages. 
 Water may be circulated in two ways, first by the natural system 
 
 39 
 
40 MOTOR TEUCK DESIGN AND CONSTRUCTION 
 
 which is termed the thermo-syphon system, and second under 
 pressure through the use of a suitable pump driven by the engine. 
 
 FIG. 29. Sectional View of an Air-Cooled Motor. 
 
 The indirect system may be described as follows : Water is cir- 
 culated from the lower water tank of the radiator through a dis- 
 tributing manifold to the lowest point of the cylinder water 
 jackets, and, as it becomes heated, its specific gravity decreases, 
 rises and flows out through the outlet manifold located on the 
 top of the cylinders, to the top of the radiator, passing into the 
 upper tank. From here it is distributed to various water pas- 
 sages through which it passes to lower tank and is recirculated. 
 These water passages are separated by air spaces for heat 
 radiation. 
 
 In the forced circulation, a pump draws water from the lower 
 tank and forces it through cylinders, as well as creating a pres- 
 
THE MOTOR COOLING SYSTEM 
 
 41 
 
 sure to force it through the water passages of the radiator. In 
 the thermo-syphon system, the pump is eliminated and circula- 
 tion is induced by the heat of the motor. The water under the in- 
 fluence of heat sets up a circulation. It can readily be understood 
 that the heat replaces the pump and 
 acts as the moving force on the water. WATER 
 
 Types of Radiators. Many different INLET 
 types of radiators have been worked out 
 since the early days of the industry. 
 The types in use at present are termed 
 the honeycomb, cellular, vertical tube 
 and vertical tube built-up types. The 
 radiator is necessarily comprised of an 
 upper and lower water tank and the 
 core in which the water is divided into 
 small streams, which are separated by 
 air passages for heat radiation as shown 
 in Fig. 30. The type of radiator is gen- 
 erally defined by the type of core used. 
 
 The true honeycomb core consists 
 of a series of six-sided or hexagonal- 
 shaped tubes fastened into the water 
 tanks in such a way as to allow of air space between the water 
 passages. This type is frail and not to the writer's knowl- 
 edge in use at present on commercial cars. 
 
 The more popular cel- 
 lular core is often called a 
 honeycomb. This consists 
 of a series of square tubes 
 placed either vertically or 
 diagonally into the tank, 
 forming a much more rigid 
 structure. The vertical 
 placing is more desirable, 
 as this provides a contin- 
 
 uous vertical tube from one 
 tank to the other. It offers 
 FIG. 31. Section of Cellular Type Core, less resistance to circulation 
 
 and is not so apt to clog up 
 
 from dirt, rust and other substances. Radiating surfaces are ap- 
 proximately equal for either construction. This construction is 
 clearly illustrated in Fig. 31. 
 
 OUTLET* 
 
 LOWER 
 
 FIG. 30. Cutaway 
 Section of Radiator. 
 
 CELLULAR 
 TYPE CO&E 
 
 WATER 
 
 A/P'^te 
 SPACES -^ 
 
 AIP 
 
42 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 FIG. 32. 
 
 The vertical tiibe type of core consists of a series of rectangu- 
 lar tubes fastened into the water tanks, with fins attached to 
 them for heat radiation, as shown in Fig. 32. The fins also ma- 
 terially assist in strengthen- 
 ing the core, and in some 
 cases they are made contin- 
 uous so that the entire con- 
 struction presents a very 
 pleasing appearance, similar 
 to the cellular type. This ver- 
 tical tube type of radiator is 
 very much in evidence on the 
 popular-priced vehicles, as its 
 first cost is considerably 
 lower than the cellular type. 
 During the past few 
 years there has been a decided 
 tendency to build up radiator 
 cores from round copper 
 tubes with separate round or 
 square cooling fins and cast 
 p water tanks, the upper tank 
 
 usually being provided with ribs to assist in heat radiation owing 
 to thicker section of metal neces- 
 sary in casting these tanks. This 
 type of radiator is illustrated in 
 Fig. 33 with a tubular core and 
 cast columns between the tanks to 
 relieve the core of the strains due 
 to the weight of the tanks and 
 water. 
 
 Another popular-priced truck 
 uses this style of radiator. How- 
 ever, the tubes are fastened to the 
 tanks by clamps in series of three. 
 This construction presents an ad- 
 vantage in the simplicity of re- 
 pair and the small cost of replac- 
 ing these sections should they be 
 
 damaged beyond repair. While this type of radiator presents 
 some advantages in strength, the writer believes that it pos- 
 
 Section of Vertical Tube 
 Type. 
 
 FIG. 33. Cast Water Tanks and 
 Built-Up Core. 
 
THE MOTOR COOLING SYSTEM 
 
 43 
 
 sesses a disadvantage in that it is not as efficient as the conven- 
 tional style mentioned above. Only a certain portion of the 
 tubes is exposed to the air currents, while the rear ones are 
 naturally limited in cooling ability, owing to being obstructed by 
 the forward ones. The volume of water is somewhat greater in 
 these tubes for the same rate of circulation, so that the cooling 
 effect is somewhat retarded. The writer has experimented with 
 both types and has come to the conclusion that the conventional 
 type is more efficient and will stand up under the most severe 
 service when spring-mounted. 
 
 FIG. 34. Mack Model "AC" Built-up-Radiator. 
 
 An unusual radiator construction is shown in Fig. 34, which 
 represents the Mack radiator for heavy duty trucks. By the use 
 of a large number of practically semi-circular sections of copper 
 tubes, which are expanded into plates that in turn are bolted to 
 the upper and lower tanks, a solderless radiator is obtained, 
 which expands within itself and withstands severe vibration with- 
 out failure. Upper and lower tanks are of aluminum alloy and 
 the upper tank forms part of the cowl, while the lower is part of 
 the frame that supports the entire unit. The tubes are expanded 
 into the plates and no solder is used in the construction. As each 
 tube is a unit in itself, one or more of the tubes can be blocked, 
 or pinched off in case of emergency without interfering with 
 others. Instead of being placed in front of the engine this ra- 
 diator is placed back of it. 
 
44 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 Mounting of Radiators. Radiators may be mounted in two 
 positions on the chassis frame; either in front of the car so that 
 the air currents pass almost unobstructed through the passage- 
 ways, or in back of the engine against the dashboard, while on 
 one particular chassis it is placed in the rear of the engine under 
 the seat. Either of the latter two positions afford a somewhat 
 more accessible engine and also afford a better protection for the 
 radiator. However, this construction requires a proportionately 
 larger radiator to obtain the same results as in the forward 
 position. 
 
 In commercial car operation the heavy vibrations accompany- 
 ing high speed on rough pavements and the distortion of the 
 
 frame, place heavy strains 
 on the radiator, so that it 
 becomes necessary to mount 
 it on springs and also pro- 
 vide a certain amount of 
 universal movement to 
 overcome frame distortion. 
 These springs maj' be of 
 
 FIG. 35. Combined Enclosed Spring flat spiral or coiled wire 
 with Front Hanger Brackets. or of round Or square sec- 
 
 tion. This support is usu- 
 ally of a three-point type, so that a limited amount of universal 
 movement is obtained. 
 
 Fig. 35 shows a popular 
 type of enclosed spring 
 mounting combined with the 
 front spring hanger brackets. 
 Brackets, riveted to each side 
 of the radiator, have exten- 
 sions, which are mounted be- 
 tween two coiled wire springs 
 in each spring bracket. This 
 bracket has a small cover plate 
 which retains the springs, FIG. 36. 
 and, together with the spring 
 bracket, supports a vertical 
 
 shaft, which acts as a guide for the radiator brackets. The 
 radiator brackets are drilled out larger than the shaft, to pro- 
 vide for a certain amount of universal movement. The top of 
 
 Universal Enclosed Spring 
 Mounting. 
 
THE MOTOK COOLING SYSTEM 
 
 45 
 
 the radiator is further supported by a stay rod which is attached 
 to the dashboard. A bumper extending from one spring bracket 
 to the other protects the radiator core from being damaged by 
 colliding with the rear end of other vehicles. 
 
 FIG. 37. Flat Spiral Spring- Mounting of the Master Trucks. 
 
 Fig. 36 illustrates another type of spring mounted radiator. 
 However, in this case a limited universal movement is obtained 
 through a clevis joint on the frame bracket, while the bumper is 
 set into the main frame channel. 
 
 FIG. 38. Onieda Eadiator Mounting. 
 
46 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 Various constructions are resorted to in practice. However, 
 they merely present different methods of accomplishing the same 
 results. 
 
 Fig. 37 shows a construction using a flat spiral spring attached 
 to the radiator. One end of the flat spiral spring is bolted to the 
 upper flange of the frame member, while the other end is rolled 
 into an eye. A bolt is inserted through the spring and side col- 
 umn to form a permanent fastening. 
 
 An excellent example of flexible mounting is depicted in Fig. 
 38 in which a pneumatic shock absorber is used. This shock ab- 
 sorber consists of a pneumatic rubber sphere placed within a 
 chamber of elliptic shape, providing a perfect cushion and acts 
 as a pivot, while it is perfectly enclosed and protected from dirt 
 and grit. This sphere is protected against excessive wear by 
 fabric pads set into the cups which form the chamber. These are 
 free to roll in any direction on the sphere, thereby relieving all 
 warping stresses, while the spheres take up all shocks and 
 vibrations. 
 
 Types of Water Pumps. There are four general types of water 
 pumps: the gear, the centrifugal, the rotary or vane and the 
 plunger types. The centrifugal is by far the most popular and 
 
 Wafer Outlet 
 
 Water Inlet 
 
 Pump 
 Casing 
 
 Packing 
 s G!cmd 
 
 ump Shaft 
 
 Drain Plug 
 
 Connection 
 Jo Radiator 
 
 FIG. 39. Sectional View of Centrifugal Pump. 
 
THE MOTOR COOLING SYSTEM 
 
 47 
 
 INLET 
 
 the gear type is next in popularity, while the rotary or vane type 
 is very little used on commercial car motors. The plunger type 
 is entirely confined to marine work, where it is used to better 
 advantage. 
 
 The centrifugal type illustrated in Fig. 39 is perhaps the sim- 
 plest of all and the easiest to understand. It consists of an im- 
 peller of paddlewheel which may either be formed integral with 
 or keved to the driving shaft and a case and cover which house 
 the rotating member. In 
 operation it is rotated at a 
 high speed, the water en- 
 tering at the center of the 
 rotating member, flowing 
 out on the arms or paddles 
 and being thrown off by 
 centrifugal force. This 
 throwing off action is re- 
 stricted by the case, so that 
 the water is forced through 
 the pump outlet. 
 
 The gear type of water 
 pump is identical with the 
 
 gear type of oil pump, with the exception of being much larger. 
 It is illustrated in Fig. 40 and it can readily be seen that it con- 
 sists of a pair of gears, a pair of shafts for them to rotate on and 
 a case with cover to serve as a housing for the gears and to carry 
 the shaft bearings. The arrows illustrate how the water enters 
 the housing through the inlet pipe and is carried around between 
 the spaces of the gear teeth and forced out through the pump 
 outlet on the opposite side of the inlet. This type of pump is 
 quite simple and was extensively used on the earlier types of 
 commercial cars. 
 
 Both the gear and centrifugal types of pumps possess an ad- 
 vantage over other types, in that they provide a continuous 
 stream of water. Between the two there is very little or no choice, 
 unless it is that the gear pump is more likely to become noisy. 
 They both do the work under substantially the same conditions. 
 
 The rotary or sliding vane pump shown in Fig. 41 consists of 
 a cylindrical housing in which is located a disc of a thickness 
 equal to the internal height of the housing, but of smaller diam- 
 eter. The disc is located eccentrically with respect to the cham- 
 
 FIG. 40. Section of Gear Pump. 
 
48 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 SLID/NO VANES 
 
 her and is cut with a diametrical slot dividing it into two halves, 
 in which slots are located two sliding vanes which are pressed 
 apart by a flat spring between them, the action of the vanes 
 
 being to carry the water 
 around to the outlet as in- 
 dicated by the arrows. 
 
 Water pumps are gen- 
 erally driven by shafts 
 extending from timing 
 gear housing and are pro- 
 vided with flexible or uni- 
 versal driving couplings. 
 The couplings serve to 
 keep the pump free from 
 strains due to misalign- 
 FIG. 41. Section of Sliding Vane Pump, ment, and they are gener- 
 ally so designed that when 
 
 the pump freezes up, the coupling will break before any damage 
 is done to the pump parts. 
 
 Fans as an Auxiliary. The motor must be cooled effectively 
 regardless of car speed. To cool a commercial car motor under 
 ideal conditions and most effectively would require a tremen- 
 dously large radiator, if the car stood still and only natural air 
 circulation were depended upon. To reduce the radiator to a 
 size that can be used, the relative efficiency is increased through 
 an artificial flow of air. This is brought about in two ways. One 
 is that the radiator does not stand still, but is moved with the car, 
 which induces an air circulation. However, this would not be 
 effective with the car standing still and the engine running, so a 
 second artificial circulation is provided through a fan. This fan 
 is driven from the engine and rotates when the engine rotates. 
 If the engine runs slowly and has little heat to dispose, the fan 
 runs slowly. Again, when the engine is running at its maximum 
 speed, the fan, too, is making its highest possible number of revo- 
 lutions." The fan serves the same purpose in an air-cooling sys- 
 tem, by forcing a draught of air over the cylinders in each 
 revolution. 
 
 This fan is generally placed at the front of the motor and 
 driven by belt from a pulley mounted on the crank shaft, cam 
 shaft, or accessory drive shaft, and draws air through the radi- 
 ator, while in the air-cooled system it draws air through a screened 
 opening at the front of the hood. 
 
THE MOTOK COOLING SYSTEM 49 
 
 Sometime ago there was a decided tendency to combine the 
 fan with the flywheel, drawing air through the radiator and over 
 the whole engine, thus effecting a secondary method of cooling. 
 In some air-cooling systems the bonnets on the engine are pro- 
 vided with deflectors so as to direct the air currents to the rear 
 cylinders, while one maker encloses the entire motor in a sheet 
 steel housing, so the flywheel draws an equal amount of air over 
 each cylinder. 
 
 5 
 
CHAPTEE IV 
 
 CAKBUEETION AND CAEBURETOES 
 
 CARBURETION is the term applied to the process of converting 
 the liquid fuel into an explosive mixture. It comprises the 
 vaporization of the fuel and the mixing of gasoline and air in 
 the proper proportion to produce the explosive mixture drawn 
 into the cylinders. The function of the air is to supply oxygen 
 for combustion. 
 
 Air is a quantity of infinite variables, since its oxygen con- 
 tent for a given volume is proportionate to its temperature. The 
 higher the temperature, the smaller the quantity of oxygen it 
 contains, without any change of carburetor adjustment. It is ac- 
 cordingly advisable to use the air at the lowest temperature at 
 which vaporization is possible. 
 
 The best proportion of air to gasoline varies between sixteen 
 to seventeen parts of air to one of gasoline ; however, this will be 
 dependent upon the quality of the fuel. 
 
 Since the power of a gasoline motor is derived from the fuel 
 which enters the cylinders during the suction stroke, it is df 
 utmost importance that the mixture of fuel and air which is used 
 by the motor, shall always be of exact proportions, so that when 
 it is ignited by the spark, it will give the maximum force of ex- 
 plosion for a given quantity of fuel. If there is too much fuel or 
 too little, within relative narrow limits, the action of the engine 
 becomes objectionable. 
 
 Vaporization of fuel may be accomplished in two ways, by 
 heat or vacuum; vaporization due to pressure reduction is dis- 
 tinguished from vaporization caused by the supplying of heat. 
 In the vacuum method, vaporization is only partly complete, no 
 matter how far the process of reduction is carried, since the part 
 of the liquid, which vaporizes, does so through the abstraction of 
 heat from the remainder, which becomes constantly colder until 
 finally the temperature is so low, that vaporization ceases until 
 heat is supplied from some outside source. When vaporization 
 is brought about entirely by heat from an outside source, the 
 degree to which it may be carried depends wholly on the amount 
 
 50 
 
CARBURETION AND CARBURETORS 51 
 
 of heat supplied, since the temperature of the liquid is being con- 
 stantly raised to or maintained at the proper point. 
 
 In practice neither of the above processes are carried to the 
 limit, but both act together. The reduced pressure, due to 
 ( ' motor suction," causes vaporization with a lowering of the tem- 
 perature, and the heat of the air tends to cause vaporization 
 through a transfer of heat from itself to the liquid. Each of 
 these vaporizing actions assist the other; the air supplying heat 
 to the liquid as it is cooled by vaporization under reduced pres- 
 sure, and the reduction in temperature, due to pressure reduc- 
 tion, facilitating the transfer of heat from the air to the liquid. 
 
 The instrument which serves to carry out the above functions 
 is known as the carburetor. Gasoline is stored in a tank, gen- 
 erally located under the driver's seat, and from here it is fed 
 through a small pipe to a compartment of the carburetor called 
 the float chamber, passing through a needle valve and strainer, 
 which regulates the amount of gasoline entering the carburetor. 
 To allow metal floats to be sustained in the gasoline they are 
 made air tight and hollow, so that the needle valve can pass 
 through them onto the valve seating. Somewhere near the top 
 of the needle valve, small weighted arms are pivoted, the ends of 
 which rest idly on the top of the float. The function of this float 
 and chamber is to maintain a constant level of gasoline in its own 
 chamber and the chamber in which the jet is located. The level 
 in the latter chamber must be constant so as to prevent the gaso- 
 line flooding over the jet, which will cause faulty running of the 
 engine. The action of the float is very much like an automatic 
 water cistern, with its ball valve, for, as more gasoline enters the 
 first chamber, the float rises, and with it the weights resting on it 
 eo that the needle valve is pushed down on its seating and shuts 
 off the supply. 
 
 The other part of the carburetor called the choke tube, or 
 mixing chamber, accommodates the jet and allows a stream of 
 air to pass around it when the piston descends on the suction 
 stroke. The float chamber maintains a constant level of gasoline 
 in the jet. When the air rushes up around the jet, it draws with 
 it a certain amount of sprayed gasoline, and, when the mixture 
 of air and gasoline impinges on the sides of the inlet manifold, it 
 becomes a gaseous mixture and enters the engine in this state 
 through the inlet valve. 
 
 Just below the manifold flange of the carburetor, and in the 
 choke tube, is located a throttle, which can be opened or closed 
 
52 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 by the operator from the lever on the steering gear or foot 
 throttle. The more gas the engine can receive, the faster it runs, 
 and the faster it runs, the more gasoline it is likely to draw from 
 the jet. This would give an unduly rich mixture, unless means 
 were provided for admitting more air, and thus giving the mix- 
 ture approximately correct proportions. For this purpose an 
 auxiliary air valve is provided, communicating with the choke 
 tube just above the jet. As the engine speed increases, this auxil- 
 iary air valve opens and permits more air to enter, thus main- 
 taining the proper mixture. It is a general assumption that more 
 air must be admitted at high speeds, but this is not really correct ; 
 for, while we are admitting more air, we are merely endeavoring 
 to keep the proportions of air and gasoline the same. Increased 
 engine speed means increased suction on the jet, and naturally 
 the liquid gasoline is drawn through faster than the air, so that 
 more air must be admitted to compensate for the excessive suc- 
 tion. But apart from speed, temperature and humidity have 
 their effect on carburetion. In the summer, the air parts require 
 to be opened wider than in winter, as the atmosphere is less 
 dense; also, when the air is damp and the barometer low, more 
 air will be necessary. 
 
 The auxiliary air valves are generally suction operated, open- 
 ing progressively as the suction increases from higher speed or 
 some other cause. If these valves could be made to have no in- 
 ertia, they would follow the suction exactly and their action 
 would be ideal. But the fact is that they open and close late. 
 Added to these faults, is that there is no way of operating them 
 that is not subject to variation. If springs are used they will 
 change in strength. A weight is effected by vibrations of the 
 car, as is also a mercury bath with a float, though to a less extent. 
 In fact numerous methods have been experimented with and all 
 found lacking in some respect. 
 
 There are many different makes of carburetors in use on com- 
 mercial car engines at present. All carburetors which are used 
 at the present time work by controlling the flow of gasoline in 
 proportion to the air demand, some attempting this by raising the 
 gasoline needle valve with the increased demands of the motor, 
 such as the Schebler and Breeze carburetors; and others accom- 
 plishing this indirectly through various air regulations and auxil- 
 iary valves, as in the Kingston, Stromberg and others. 
 
 Some carburetors operate automatically, while others are so 
 arranged that they may operate both automatically and me- 
 chanically. 
 
CARBUKETION AND CAKBUEETOKS 
 
 53 
 
 This principle of automatic carburetion, which is employed 
 in the majority of modern carburetors, may be outlined as 
 follows : 
 
 A correct mixture having been obtained for the minimum 
 suction on which the motor is capable of running, is compensated 
 by the introduction of additional air at a rate varying auto- 
 matically with the suction. The mechanical operation is obtained 
 by connecting the butterfly valve, which controls the admission 
 of gases from the carburetor, w r ith the butterfly valve in the 
 main air opening, the automatic operation of the auxiliary valve 
 being retained. 
 
 During the past year there has been a tendency to provide 
 dashboard adjustments, so that the mixture may be instantly 
 varied throughout the entire range for heavier or lighter work, 
 or because of other changing conditions. This is generally ac- 
 complished by varying the pressure of the auxiliary air valve 
 spring. They are quite an advantage, as it is claimed that an 
 automatic carburetor cannot adapt itself to changes in gasoline 
 density, or in humidity, or to the gradual warming up of an 
 engine when started from cold. 
 
 It would require too much space to illustrate all the various 
 makes of carburetors used on the various commercial car engines, 
 so the writer will present a 
 few illustrations, which are 
 explanatory of the various 
 types discussed in this ar- 
 ticle, such as the raised 
 needle valve type, the indi- 
 rect type, and automatic 
 and mechanically operated 
 types. 
 
 Fig. 42 is a sectional 
 view of the Model "L" 
 Schebler carburetor, which 
 is of the raised needle type, 
 and is so designed that the 
 amount of fuel entering the 
 motor is automatically con- 
 trolled by means of a raised needle seating in the jet, working 
 automatically with the throttle. The float and its chamber sur- 
 round the main air supply in which the jet is located. The jet 
 
 THROTTLE lfVa 
 
 FLOAT CHAMBER 
 
 FIG. 42. Sectional View of Schebler 
 Carburetor. 
 
54 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 FLOAT 
 
 FIG. 43. 
 
 Section of Kingston Car- 
 buretor. 
 
 opening is controlled by a needle, which permits of a variable 
 opening as the throttle is opened or closed, being operated by a 
 
 cam on the throttle lever. 
 The aux ii iary a ir valve is 
 controlled by the suction of 
 the motor, while the mix- 
 ing chamber is water jack- 
 eted to apply heat to assist 
 in vaporization. The main 
 air supply can also be con- 
 nected with a drum around 
 the exhaust manifold for 
 supplying warm air. 
 
 Fig. 43 is an illustra- 
 tion of the Kingston car- 
 buretor, which is provided 
 with an adjustable jet sur- 
 rounded by the float and 
 chamber. The main air in- 
 take communicates with 
 
 the mixing chamber, while the auxiliary air enters through five 
 circular openings ar- 
 ranged in a semi-circle 
 above the mixing cham- 
 ber, and controlled by 
 floating balls. These balls 
 are so arranged that they 
 cannot become displaced. 
 They operate automat- 
 ically, gradually lifting 
 from their seats as the 
 motor suction increases. 
 The air passing the open- 
 ings guarded by the balls 
 has an unrestricted pas- 
 sage into the mixing 
 chamber, and then to the 
 motor. The main air in- 
 take is fitted with a but- 
 terfly throttle, so that the 
 amount of air can be reduced for starting, around the nozzle of 
 
 JET ADJUSTING 
 SCREEN 
 
 FIG. 44. Holley Carburetor in Section. 
 
CARBURETION AND CARBURETORS 
 
 55 
 
 THROTfLC VALVE 
 
 the jet, is a well, which becomes partially filled with gasoline 
 while the motor is idle. This is brought about automatically by 
 the level of the gasoline in the float chamber being slightly higher 
 than the top of the jet. This gives a rich mixture for starting, 
 and as long as the motor is running the gasoline is drawn through 
 the jet into the intake manifold, the well remaining dry. 
 
 Some of the features of the Holley carburetor, illustrated in 
 Fig. 44, are concentric float, adjustable jet, supplementary stand- 
 pipe for starting and slow running and absence of air valves. 
 Gasoline enters and passes through a strainer A and passages H 
 into the jet. This jet is controlled by a milled screw, so that the 
 opening can be varied at will. Gasoline passes into the jet M, 
 which is in the shape of a venturi, or double-ended cone, and also 
 into the standpipe /, to 
 a level determined by the 
 float. This standpipe 
 leads to the edge of the 
 butterfly throttle, and 
 when the latter is closed, 
 the suction of the motor 
 allows gasoline to be 
 drawn up into the stand- 
 pipe, past the plug K, and 
 into the manifold. After 
 the motor has been started, 
 and the throttle opened, 
 the gasoline is drawn 
 through the main jet J/, 
 mixing with the air that 
 enters from below, through 
 the conduit N. 
 
 Fig. 45 illustrates the 
 Fierce-Arrow automatic 
 
 carburetor, with concentric float and adjustable jet. The gasoline 
 supply from the tank passes through a fine gauze strainer, pre- 
 venting water and dirt from entering the float chamber. The 
 main air supply is taken through the lower inlet, and, coming 
 from the proximity of the exhaust pipe, is warm, and passes up 
 around the spray nozzle A. The auxiliary air is taken through 
 two reed valves, which are controlled by flat springs. When the 
 engine runs slowly, both auxiliary valves remain on their seat, 
 and as the engine runs faster, the more intense suction opens the 
 
 FIG. 45. Section of Fierce-Arrow Car- 
 buretor. 
 
56 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 FIG. 46. 
 
 Sectional View of Stromberg 
 Carburetor. 
 
 lighter reed valve, admitting air above the spray nozzle. A 
 further increase in engine speed opens the heavier reed valve, per- 
 mitting still more air to 
 enter. 
 
 The Stromberg carbu- 
 retor (Fig. 46) is a double 
 jet type, featuring an ec- 
 centric float chamber with 
 a glass wall, a feature 
 which is typical of all 
 Stromberg models. The 
 flow of gases is controlled 
 by a butterfly valve placed 
 over the mixing chamber 
 and immediately over the 
 venturi, in which the main 
 jet C is located. The sec- 
 ond jet, /, comes into op- 
 eration as the speed of 
 
 the motor increases enough to permit the auxiliary air valve to 
 open. The main air passage can be entirely or partially closed 
 for starting purposes, and 
 this operation also pre- 
 vents the auxiliary air 
 valve from opening, the 
 latter being of the mush- 
 room type, provided with 
 two adjustments. The 
 valve has two spindles, 
 one above and one below 
 the seat, each spindle hav- 
 ing a spring encircling it, 
 finer adjustment being 
 claimed for this construc- 
 tion. The body of the car- 
 buretor is not water jack- 
 eted, heat being supplied 
 through the open air pipe 
 
 from a drum surrounding FlG . 47. Carter Carburetor in Section. 
 
 the exhaust manifold. 
 
 The features of the Carter carburetor, illustrated in Fig. 47, 
 are eccentric float, shock-absorbing needle valve control and ver- 
 
CARBURETION AND CARBURETORS 57 
 
 tical multiple jet fuel tube. Gasoline enters the float chamber in 
 the usual way. However, the needle valve is provided with a 
 small shock-absorber, as no permanent connection is made be- 
 tween the float and the lever controlling this valve. 
 
 The tube, located in the funnel, has a multiplicity of small 
 holes arranged spirally around the tube, and, as a vacuum is 
 created in the carburetor by the suction of the motor, the fuel 
 rises and falls instantaneously in the tube, according to the speed 
 of the motor. As the fuel rises in the tube, it is sprayed out of 
 the jets, and, owing to the minuteness of the jets and the force 
 with which the fuel emerges, the gasoline is broken up into very 
 small particles and converted into a mist. The spiral arrange- 
 ment of the jets insures each one a separate supply of air. This 
 fuel tube is adjustable for low speeds, while the intermediate ad- 
 justment is obtained through the auxiliary air valve. The high 
 speed adjustment is an air control in the funnel carrying the fuel 
 tube. A strangling tube connected with the float chamber is also 
 provided for easy starting. 
 
 Many of the so-called carburetor troubles are not really the 
 fault of the carburetor at all. Air leaks along the path of the 
 gas in the cylinder will upset the action of the best carburetors 
 made. The air leaks may be caused by defective gaskets between 
 the manifold and the cylinder, or manifold and carburetor, or by 
 loose studs, nuts or cap screws in these connections. These air 
 leaks destroy the quality of the mixture, and also reduce the 
 vacuum created by the motor, so that a much smaller charge 
 enters the cylinders. Mixture proportion may also change, due 
 to some disarrangement of the auxiliary air valve, as by the 
 slackening of the nuts controlling the spring. On the present 
 day models this difficulty is overcome by locking these nuts with 
 split pins. Another source of trouble is the stoppage of the feed 
 line from the tank to the carburetor, due to foreign matter in the 
 gasoline. There is a noticeable tendency this year towards the 
 use of strainers to remove these impurities. 
 
 The general concensus of opinion among the makers of car- 
 buretors is that, for commercial car motors, the mixture should 
 be heated by some means before entering the cylinders. There 
 are numerous ways of accomplishing this, by water jacketing the 
 carburetor or intake manifold, and by supplying heat from the 
 exhaust manifold, either directly to the mixture, or by a heat 
 jacket around the mixing chamber of the carburetor. 
 
58 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 Carburetors are made with or without water jackets, while 
 the hot-water supply is generally taken from the pump through 
 a small pipe and returned to the cylinders. The flow is controlled 
 by shut-off cocks, so that it may be shut off during the summer 
 months, when better results are obtained without the aid of heat. 
 Hot air from the exhaust manifold may be circulated and con- 
 trolled in a like manner. 
 
 In some motors, part of the intake manifold passes through 
 
 the water jacket of the cylinders, so that heat is supplied to the 
 
 charge. The direct method is by connecting the main air pipe of 
 
 the carburetor with a drum, placed around the exhaust manifold, 
 
 so that the air is always preheated. 
 
 It is quite difficult to state which of the above methods are the 
 best, as this is to some extent dependent upon the design of the 
 carburetor. One method might work well on a certain carburetor 
 and absolutely fail on another make. 
 
 Carburetors are generally bolted to flanges of the intake mani- 
 fold; however, the heavy vibrations existing in commercial car 
 operation have led some makers to provide separate brackets on 
 the crank case of the engine to take the weight of the carburetor 
 and to prevent the adjustments from becoming disarranged due 
 to the vibration. 
 
CHAPTER V 
 
 IGNITION SYSTEMS 
 
 High-tension Magnetos of Independent and Dual Types. A 
 considerable number of articles have been written on ignition 
 systems, with the object of explaining the operation of the mag- 
 neto and battery systems. However, the writer will attempt to 
 cover this subject in such a way as to enable the laymen to ac- 
 quaint themselves with the action of the magnetos on commercial 
 car motors without mastering electrical theories. The subject is 
 a broad one, and even the following may seem unnecessarily long, 
 but it should be remembered that a magneto is a complicated in- 
 strument and any description in few words must necessarily be 
 superficial and can be of little value. 
 
 Three Types. For ignition purposes the magneto is at present 
 considered the most efficient device. There are three main types 
 of magnetos on the market. First, the low-tension magneto, 
 with step-up coil, furnishing a jump spark. Second, the low- 
 tension magneto in connection with the make and break system. 
 Third, the high-tension magneto, furnishing a jump spark. 
 
 Low Tension for Jump Spark. The first system is largely 
 used, having the advantage of low first cost, but necessitates con- 
 siderable complications and in reality is a high-tension system; 
 as the spark is made to jump across the air gap between the spark 
 plug electrodes, with the use of the step-up coil. The air which 
 lies between the two electrodes is a non-conductor and is an ob- 
 stacle to the flow of electrical current, so that a very high elec- 
 trical pressure is needed to send a spark through it; therefore, 
 all different methods which involve a spark plug may be called 
 high-tension systems. The ultimate object of all ignition systems 
 is to get a spark between two conductors located in the engine 
 cylinders. 
 
 Low Tension for Make and Break. The second system is very 
 rarely used on commercial cars at present, being discarded owing 
 to its mechanical complications and the large amount of atten- 
 tion required to keep it in working conditions. In this system 
 the spark plugs are discarded and two conductors are so arranged 
 
 59 
 
60 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 that they actually touch each other in the cylinder. One con- 
 ductor is fixed and insulated from the cylinder, while the other is 
 arranged to be moved by a mechanical mechanism, so that a gap 
 is created, through which the spark passes. 
 
 High Tension for Jump Spark. The third system is now the 
 most popular, as the high tension is produced directly in the 
 armature winding of the magneto, without the use of a coil or 
 other auxiliary. The wiring is also the simplest, as it consists of 
 high-tension wires to each spark plug and a low-tension wire to 
 the switch on the dash. 
 
 The principal difference between the high-tension and the 
 low-tension ignition systems is, that in the high-tension system 
 there is an incomplete circuit and a spark must be driven across 
 an air gap ; whereas, in the low-tension system an electric current 
 already flowing in a conducting circuit is driven by its own 
 momentum across an air gap which is suddenly formed on it. 
 
 For high-tension, what is needed is a very hot spark of high 
 frequency, positive and of a certain length to penetrate the air 
 space between the electrodes of the spark plugs, which is gen- 
 erally from 1/64 to 1/32 in. 
 
 Basis of Classification. Magnetos are classified in two groups, 
 according to the basic principles employed in the magnetic field 
 to generate the initial electrical impulses. These two classes are 
 known as the armature and conductor type. 
 
 In the former, electrical current is generated by revolving 
 several thousand feet of fine copper wire, which is wound around 
 a soft iron core, between the pole pieces of the magneto. As the 
 winding rotates within its narrow confines, electrical impulses are 
 set up within the winding. 
 
 The above types may again be divided into two classes. One 
 is called the primary armature magneto and the other is called 
 the compound armature type. The primary type has but a single 
 winding in the magnetic field and generates a low voltage cur- 
 rent. It requires an outside transformer coil to step up the cur- 
 rent to the high potential required at the spark plug. The com- 
 pound armature type incorporates a second winding, or sec- 
 ondary winding, also upon the armature shaft. In addition, a 
 condensor must be incorporated in the magneto. 
 
 The inductor type consists of revolving a solid steel shaft, 
 upon which are mounted two steel fan-shaped inductor wings, 
 within a stationary winding in the magnetic field. 
 
IGNITION SYSTEMS 61 
 
 High Tension in Detail. The high-tension magneto is not only 
 a current generator, or a substitute for the battery, but combines 
 all the elements of a complete ignition system except the spark 
 plugs and the switch. It generates the current, transforms it to a 
 high pressure and distributes the high-tension current to the 
 cylinders. 
 
 The structural portion of the magneto consists of permanent 
 magnets of inverted U-shape, sometimes referred to as horseshoe 
 magnets. Two such magnets are generally used on the smaller 
 magnetos, while four are used on the larger ones. The free ends 
 of these magnets are termed the poles, one as the north and the 
 other as the south pole. To these poles are secured soft iron 
 blocks, known as pole pieces or pole shoes. The magnets and pole 
 pieces are mounted upon a non-metallic base, while the pole 
 pieces are bored out cylindrically to receive the armature, which 
 is of substantially cylindrical form. This armature consists of a 
 soft iron core of H section, and serves to form a bridge for the 
 magnetic flux between the pole pieces and also to carry the wind- 
 ing in which the current is induced. After the core has been 
 properly insulated, several layers of heavily insulated wire are 
 wrapped around it. To the end of this heavy wire the beginning 
 of a very fine silk-insulated wire is connected and the wire is 
 wound on the core until the slot is almost filled. After the outer 
 insulating cloth is in place, bands are put around the circum- 
 ference of the armature to hold the winding in place under high 
 armature speeds. The end plates which form the shafts are then 
 attached. 
 
 The heavy or primary winding serves primarily to generate 
 the current, and in connection with the fine or secondary winding, 
 also serves to multiply the pressure or voltage to such an extent 
 that it will produce a spark between the electrodes of the spark 
 plug in the cylinder. 
 
 Magnetic Lines of Force. It has been found by experiment 
 that there is an attractive and repulsive force between magnets, 
 and that this magnetic force pervades the surrounding space. 
 The fact that a magnet when suspended near another magnet 
 will take a certain direction, depending upon the relations of 
 the poles, has led to the conception of the magnetic lines of 
 force, which emanate from the north pole of the magnet and pass 
 through the -surrounding atmosphere to the south pole. 
 
 In a magneto the magnetic lines of force flow from the pole 
 piece of the north pole to the pole piece of the south pole through 
 
62 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 the armature and the air gap between the armature core and the 
 pole pieces. The space between the pole pieces is termed the mag- 
 netic field. 
 
 The magnetic lines of force which pass through the armature 
 are variously distributed according to the position of the arma- 
 ture in rotation. This is true because the magnetic lines of force 
 pass more readily through the sides of the H than through the 
 wiring laid between them. 
 
 Any movement of the armature on its shaft, either in making 
 a complete revolution or in oscillating backward and forward, 
 must operate to deflect and distort these lines of force in such a 
 manner as to set up powerful induced currents in the armature 
 winding. 
 
 Induction of Electrical Impulses. Four positions of the mag- 
 neto armature are shown in Fig. 48. At A the magnetism is rep- 
 resented as passing through the soft iron core, the heads of which 
 are in close proximity to the pole pieces and threading the arma- 
 
 FIG. 48. Magneto Armature Positions. A, Magnet. B, Pole Piece. 
 
 C, Armature. 
 
 ture winding. At B the armature has passed to a point where its 
 heads are just passing out of proximity of the pole pieces, and 
 thus breaking the magnetic path between the pole pieces. At this 
 point a sudden generation of electrical pressure is taking place 
 in the armature winding, this causing a current to flow in it. 
 When the armature reaches position C its core again forms a 
 path for the passage of magnetism from pole piece to pole piece 
 and the current becomes zero again. At D the same condition 
 exists as in B, although in the opposite direction. 
 
 Thus, in each revolution two electrical impulses in opposite 
 directions are induced in the primary winding of the armature. 
 These impulses last only for a small fraction of the time of a 
 revolution and are equally spaced. The electromotive force, or 
 
IGNITION SYSTEMS 63 
 
 tension, of these is very low and entirely insufficient to cause a 
 spark to jump between the spark plug electrodes, separated by 
 even the shortest air gap. 
 
 Giving the Impulses Sufficient Strength. The next step con- 
 sists in transforming these impulses, or multiplying their pres- 
 sure several thousand times. It is for this purpose that the fine 
 wire winding is provided on the armature. When the armature 
 is being rotated between the pole pieces an electromotive force 
 is being induced in the secondary or fine wire winding, the same 
 as in the primary or course wire winding and many times greater, 
 but still not sufficiently great to bridge the spark plug electrodes. 
 
 The primary winding is ordinarily closed upon itself. This 
 causes a current to flow in it more or less proportional to the 
 electromotive force. That is, the current is at a maximum when 
 the armature is in a vertical position. At that time there are 
 practically no lines of force from the permanent magnets pass- 
 ing through the central part of the core. But the heavy current 
 flowing in the primary winding makes of the core an electro- 
 magnet, setting up a magnetic field at right angles to that of the 
 permanent magnets. Now, if at this moment the primary cir- 
 cuit be suddenly opened, the current in it will almost instantly 
 cease flowing and the magnetism set up by this current will 
 vanish. These lines of force are also included by the turns of 
 the secondary winding, and as they are withdrawn so exceedingly 
 rapidly, and since there are such a large number of turns in the 
 secondary winding, the result is that an enormous electromotive 
 force is induced in the secondary winding, which will cause the 
 spark to bridge a gap in the atmosphere of from one half to 
 three fourths inch long. 
 
 The Circuit Breaker. A device known as the circuit breaker, 
 or interrupter, is used to open and close the primary circuit. This 
 is carried on the armature shaft opposite the driving end of the 
 magneto. 
 
 It is represented in Fig. 49 and consists of a stationary con- 
 tact A and a movable contact B on the arm C. Both of these 
 parts are mounted on a brass disc Z>, which is securely fastened 
 to the armature shaft and rotates with it. The stationary con- 
 tact A is insulated from the disc />, while the movable contact B 
 is in metallic contact with it, and the disc D is grounded to the 
 frame of the magneto by a grounding brush. The circuit breaker 
 is surrounded by a cylindrical housing F, to the interior of which 
 
64 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 at diametrically opposite points are secured steel cam blocks, 
 G-G. Ordinarily these two contact points are kept in contact by 
 a spring. As the disc D rotates, the outer end of the arm C comes 
 in contact with the cam blocks G, whereby A and B are sep- 
 arated momentarily. As soon as the cam block G has been passed, 
 a spring brings the two contact points together again. Sta- 
 tionary contact A is connected with one end of the primary wind- 
 ing of the armature, while the other end has a metallic connec- 
 tion with the armature core; or in other words, is grounded. 
 
 G 
 
 FIG. 49. Diagram of Circuit Breaker. 
 
 When these two contact points are suddenly separated, there 
 is a tendency for the current to continue to flow across the gap, 
 it possessing a property similar to the inertia of matter. This 
 would result in a hot spark being formed between the two con- 
 tact points, which would not only burn the points away rapidly, 
 but would also prevent a rapid cessation of the current. 
 
 The Condenser. To avoid this, a condenser is used, which is 
 built into the magneto. This condenser consists of two sets of 
 tinfoil sheets, sheets of opposite sets alternating with each other, 
 and being separated by sheets of insulating material. All the 
 sheets of each set are metallically connected, and one set is con- 
 nected with the primary winding, while the other set is grounded. 
 These condensers are capable of absorbing an electrical charge, 
 and their capacity is so proportioned that they will take up the 
 entire charge of extra current produced when the contact points 
 
IGNITION SYSTEMS 65 
 
 of the circuit breaker separate that is, the extra current instead 
 of appearing in the form of a spark across the gap, passes into 
 the condenser. 
 
 Controlling the Point of Ignition. The magneto armature is 
 positively driven from the motor crankshaft and the current im- 
 pulse in the armature always occurs when the piston is in a cer- 
 tain position. Since in regular operation of the motor the charge 
 is ignited just an instant before the completion of the compres- 
 sion stroke, the magneto armature is so set relative to the engine 
 crankshaft that the maximum induction effect occurs at this 
 moment. This construction is termed a fixed spark. However, 
 quite a few users demand a variable spark; or in other words, 
 to vary the time of the cycle when ignition occurs. In order to 
 make this possible, the circuit-breaker housing F is so arranged 
 that it can be rocked around its axis, being provided with a lever 
 arm for this purpose, which is connected with the spark lever on 
 the steering gear. 
 
 In the Mea magneto, owing to its construction, the circuit 
 breaker and the magnets are moved around their axis so that the 
 armature will hold its relation to the pole pieces, whether ad- 
 vanced or retarded. 
 
 An Automatic Control. One model of Eiseman magneto in- 
 corporates an automatic spark advance, which is accomplished 
 by the action of centrifugal force on a pair of weights attached 
 to one end of a sleeve, through which runs the shaft of the mag- 
 neto, and hinged at the other end of the armature. Along the 
 armature shaft run two helicoidal ridges, which engage with sim- 
 ilarly shaped splines in the sleeve. When the armature is rotated, 
 the weights begin to spread and exert a longitudinal pull on the 
 sleeve, which in turn changes the position of the armature with 
 reference to the pole pieces. In this way the moment of the 
 greatest induction is advanced or retarded, and with it the 
 breaker in the primary circuit. 
 
 The Distributor. The high-tension current is distributed to 
 the spark plugs in the following manner: One end of the sec- 
 ondary winding is grounded through the primary winding, since 
 it is attached to one end of the primary, the other end of which is 
 grounded. The other end of the secondary generally leads to the 
 collector ring, from which the current is taken off by a carbon 
 brush. From here the current is carried through a spring con- 
 tact conductor to a distributor on the magneto. This distributor 
 
66 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 consists of an insulated disc, in which are imbedded on the inner 
 side one central contact piece and four or six sector-shaped con- 
 tact pieces, the number depending upon the number of cylinders 
 on the engine. This distributor also comprises a shaft which 
 carries a gear wheel meshing with another on the armature shaft. 
 The reduction between these gears is two to one, so that the arma- 
 ture shaft makes two turns. The large gear wheel carries a brush 
 holder, containing a carbon brush, which makes contact simul- 
 taneously with the central contact piece and one of the sector- 
 shaped contact pieces, which are connected by means of wiring 
 or cable to the spark plugs. 
 
 A magneto must be so designed that it will give a sufficiently 
 hot spark at a comparatively low engine speed. This ability im- 
 plies the ability of generating very large and hot sparks and 
 enormously high tensions at high engine speeds. 
 
 The Safety Gap. The electromotive force generated in the 
 secondary winding is limited to the size of the spark gap of the 
 spark plugs; for, as soon as the tension reaches a point sufficient 
 to jump this gap, the discharge occurs and there is no further 
 increase in the electromotive force. If, by chance, the gap be- 
 tween the spark plug electrodes become large enough that there 
 is no chance for the sparks to pass in the ordinary way, the elec- 
 tromotive force in the secondary winding might build up to such 
 an extent as to puncture the insulation of the winding and ruin 
 the armature. To avoid this, a safety gap is provided in which 
 the gap is larger than in the spark plugs. Under ordinary con- 
 ditions, no spark will pass between the two terminals of the safety 
 gap. However, should the condition mentioned above arise, a dis- 
 charge will Occur at the safety gap, preventing the electromotive 
 force from rising still higher. 
 
 Function of the Switch. In order to stop the magneto from 
 producing sparks, when it is desired to shut down the motor, a 
 switch is provided. One terminal of the switch is grounded to 
 the engine or frame, while the other is connected to a binding 
 post on the circuit-breaker housing. This binder post is, in turn, 
 connected with the contact points of the circuit breaker. When 
 the switch is closed, the current generated in the primary wind- 
 ing flows to the contact points and through the binding post and 
 connecting wire to the switch, whence it passes through a wire 
 to the frame work of the car and return to the beginning of the 
 primary winding. In other words, the switch cuts out the cir- 
 
IGNITION SYSTEMS 
 
 67 
 
 cuit breaker and the primary winding is short circuited all the 
 time, so that the opening and closing of the contact points has no 
 effect. 
 
 Summary of Independent System. Fig. 50 shows the path 
 of the primary circuit originating in the primary winding of the 
 armature. It flows through the contact breaker screw to the sta- 
 tionary contact point, thence across to the movable contact point, 
 
 SPARK PLUGS 
 
 PRIMARY WINDING 
 SECONDARY WINDING 
 
 - FRAME 
 
 iSAFETY SPARK GAP 
 
 DISTRIBUTOR PLATE 
 
 - 
 
 V_. _l L.. 
 
 FIG. 50. Path of Primary Circuit, Originating in the Armature. 
 Primary Winding. 
 
 from where it is led through the contact brush in the framework 
 of the magneto, whence it returns to the beginning of the primary 
 winding, which is also connected or grounded to the frame. The 
 beginning of the secondary winding is connected to one end of 
 the primary winding, and* since one end of the primary is 
 grounded, the secondary is also grounded through the primary. 
 The other end of the secondary winding leads to the insulated 
 collector ring, from which the current is taken off by a carbon 
 contact brush. From the brush holder the current is carried 
 through a spring contact conductor to the distributor, from 
 where it is distributed to the spark plugs. 
 
 Dual Systems. So far high-tension magnetos of the inde- 
 pendent type have been discussed. However, most all magneto 
 makers also build high-tension magnetos, which provide a dual 
 ignition system, using a battery and coil with one set of spark 
 
68 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 plugs. Some makers use the magneto breaker for the battery cur- 
 rent, while others provide a separate circuit breaker to avoid the 
 possibility of both systems being put out of commission by an 
 accident affecting only one, but subsequently extended to the 
 other on account of its close relationship. The same distributor 
 is used for both systems. 
 
 The Coil. The battery current is of a low tension and con- 
 nected with a two-point switch on the coil. From the coil the 
 current is led to the circuit breaked, and, as the circuit is broken 
 
 SWITCH HANDLE (CAN BE REMOVED) 
 
 TO THE PLUGS 
 
 - HIGH TENSION CABLE (/ 
 LOW TENSION CABLE (I 
 
 %To%"ntieii) 
 
 FIG. 51. Wiring. Diagram of Eiseman Dual-Ignition System. 
 
 at the proper moment, a very high voltage is induced in the sec- 
 ondary of the coil or transformer, and being delivered to a heavily 
 insulated cable, is conducted to the central carbon brush of the 
 distributor, whence it is delivered to the spark plugs in the dif- 
 ferent cylinders in correct sequence. 
 
 The coil has a primary and secondary winding, similar to 
 that of the armature of the magneto, and performs the same 
 function in the battery circuit, being provided with a separate 
 condenser. 
 
IGNITION SYSTEMS 69 
 
 Fig. 51 is a wiring diagram of the Eiseman dual ignition sys- 
 tem. The high tension is led from the collector ring of the mag- 
 neto of HM and led to TIM on the coil, thence to the switch H on 
 the coil and to H on the magneto. When the coil handle is 
 shoved over to the battery position, several operations take place 
 in the switch of the coil. First, the primary current, emanating 
 from the terminal MA of the magneto, is led to the ground or 
 body of the magneto, and this prevents it from generating a high- 
 tension current. Second, the battery current is allowed to flow 
 in the coil at + on the coil, through the coil, thence to R on the 
 coil to R on the magneto, where it is interrupted by a circuit 
 breaker, thence it returns to the battery through the ground. 
 When it is desired to stop the motor, the coil handle is moved to 
 the off position, cutting off the battery current and the magneto 
 current remains short circuited, thus eliminating all ignition. 
 
 Operation of Switch. But, if instead of leaving the handle at 
 " off," it is quickly shoved from " Bat," to " Mag," without ar- 
 resting it between the two, the motor begins to run on the mag- 
 neto current. In this case the battery current is left cut off as in 
 the " off " position, while the connection, which in both the other 
 positions has led the primary circuit of the magneto to be ground, 
 is broken, with the result that this current is diverted to the 
 breaker mechanism on the armature shaft, thus generating in 
 the secondary winding of the magneto the high-tension current 
 led to the spark plug. 
 
 The same distributor is used for the battery high-tension cur- 
 rent, for, when the switch is on " Bat," there is a connection 
 made between the end of the coil's secondary winding and the 
 terminal H on the coil, which sends the battery current over the 
 same route as that of the magneto. 
 
 Before the motor is in motion, the interrupter R, still re- 
 ferring to Fig. 51, cannot operate, and this makes necessary in- 
 terruptions by hand with a starter knob when starting from the 
 seat on compression. This takes the place momentarily of the 
 circuit breaker, being supplanted by the latter the moment the 
 engine turns over. 
 
 Low-tension Magneto and Battery Systems. As mentioned in 
 the above, all systems using a spark plug are termed high-tension 
 systems; however, a low-tension magneto may be used with a 
 transformer coil. Eeference was made to the instrument having 
 a single winding on its armature and employing a step-up coil 
 
70 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 with a primary and secondary winding. This type, termed a 
 high-tension system, although a low-tension current is obtained 
 from the instrument itself. However, this low-tension current is 
 transformed into a high-tension by the coil. 
 
 These coils are similar to those used in connection with bat- 
 tery systems, and as but few more wires are necessary to use a 
 battery current, the system is generally of the dual type, making 
 use of the magneto interrupter and distributor for both magneto 
 and battery current. The low-tension magneto is sometimes de- 
 fined as the primary armature type, as it incorporates but a single 
 or primary winding in the magnetic field. 
 
 The construction of a low-tension magneto is similar to that 
 of the high-tension type. It consists of permanent magnets of 
 inverted U-shape, and the pole pieces bored out cylindrically, 
 mounted upon a non-metallic base. The armature is also of H 
 section, carries a primary winding and serves to form a bridge 
 for the magnetic flux between the pole pieces. The armature 
 core is wrapped with primary wire until the slot is almost filled. 
 The insulating cloth is then put in place and the armature 
 banded. 
 
 A low-voltage current is furnished by the magneto armature 
 to the primary winding of the coil, while a secondary winding in 
 the coil transforms this to a high voltage. 
 
 The interrupter and distributor are similar to the high-ten- 
 sion type and perform the same functions in the system. 
 
 The main constructive difference between the low and high- 
 tension types is that the former has but one winding on the arma- 
 ture, using a transformer coil to raise current pressure value, 
 whereas the high-tension type has a secondary winding incor- 
 porated in the armature. 
 
 The principle of a rotating armature and the method of gen- 
 erating current in the magnetic field was explained previously. 
 We may now discuss the method of transforming the low -tension 
 current to a high tension. 
 
 Fig. 52 is a wiring diagram of this type, with external trans- 
 former coil. It will be noted that the primary winding of the 
 transformer is so connected with the magneto armature winding 
 that it completes the metallic circuit through the latter. That is, 
 the transformer primary is in series with the armature winding. 
 The breaker points are separated at definite intervals, and are so 
 connected into the armature and transformer primary circuit 
 that a direct short circuit through the armature winding is 
 
IGNITION SYSTEMS 
 
 71 
 
 caused when they are in contact. The breaker points are here 
 said to be connected in parallel with the transformer primary. 
 
 As the induced electric 
 pressure within the armature 
 winding rises in value, due to 
 the motion of the armature 
 in the magnetic field, it flows 
 through the circuit formed 
 by the armature winding and 
 the circuit breaker points un- 
 til the instant at which it has 
 attained its maximum value, 
 when the contact points are 
 separated and the direct short 
 circuit broken. When this 
 separation of the points oc- 
 curs, the induced electric pres- 
 sure is caused to enter the 
 transformer primary with 
 great suddenness and create 
 lines of force through the 
 transformer windings with 
 extreme rapidity. This entry 
 by the current and consequent 
 creation of lines of force 
 causes the lines to cut the sec- 
 ondary winding during the 
 formation of the magnetic 
 field about the transformer, 
 and this cutting induces an 
 Ex electrical pressure within the 
 secondary. 
 
 Of course with this sys- 
 tem the armature of the magneto is positively driven from the 
 engine by gears, so that the points of maximum pressure induc- 
 tion in the armature winding may coincide with the instants at 
 which ignition sparks are desired within the engine cylinders. 
 Such a single transformer with a single breaker is employed and 
 all the current for ignition is generated therein; it is necessary 
 that some means be fitted for the distribution and consecutive 
 connections of the transformer secondary with the proper spark 
 
 FIG. 52. Wiring- Diagram for 
 Low-Tension Magneto with 
 ternal Transformer Coil. 
 
72 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 plugs in the cylinders. This distribution is accomplished by a 
 distributor, also made an integral part of the magneto, and 
 driven positively and in a definite relationship with the circuit 
 breaker as in the high-tension type. 
 
 Again referring to Fig. 52, it is seen that the ends of the trans- 
 former secondary winding are connected, for the completion of 
 its circuit through the spark plugs, one to engine frame, or in 
 other words, one end is grounded and the other the central car- 
 bon brush holder of the distributor. 
 
 This distributor is of the same construction as in the high- 
 tension system, so that the high-tension current induced in the 
 secondary winding will be forced to follow the path selected for 
 it, depending upon the position of the carbon brush of the dis- 
 tributor. In this illustration the heavy lines illustrate the pri- 
 mary circuit and the light lines the secondary circuit. 
 
 Most coils in use at the present writing are of the non-vibrat- 
 ing type, the trembler type of box coil having been discarded 
 long ago, and the interrupter is now operated mechanically in- 
 stead of electrically. 
 
 These non- vibrating or transformer coils, as they are termed, 
 are made in various styles, and sometimes incorporate the switch 
 and a push button for starting on the spark. 
 
 The most popular type 
 is the tube coil with 
 switch, which can be 
 mounted on the dash un- 
 der the hood with switch 
 on the outside, within 
 reach of the operator. In 
 some cases the coil is made 
 separately and mounted 
 under the hood, while the 
 switch has the usual posi- 
 tion on the dash. 
 
 Fig. 53 illustrates the wound core of a transformer coil, com- 
 plete with condenser casing. These coils are mounted in a tubular 
 case provided with front and rear end plates. The front plate 
 carries the switch handle and push button, while the rear end 
 carries the terminals and is enclosed by a cover, so that the coil 
 and connections are thoroughly protected. 
 
 The push button is used for producing a spark in the cylinder 
 by interrupting the primary circuit leading from the battery. 
 
 /CONDENSER 
 
 'INSULATED 
 WINDINGS 
 
 FIG. 53. Transformer Coil. 
 
IGNITION SYSTEMS 
 
 73 
 
 taking the place momentarily of the breaker on the magneto. 
 Some coils are fitted with a ratchet mechanism giving a series 
 of sparks in the cylinder. Some are also provided with a lock 
 and key, so that the switch may be locked in the " off " position, 
 preventing the unauthorized use of the truck. 
 
 The action of the switch was explained previously in connec- 
 tion with the dual system, and requires no further discussion. 
 
 FIG. 54. Wiring Diagram of an Induction Coil and the Other Components 
 of a Battery System. 
 
 The battery system, providing a jump spark, was extensively 
 used before the magneto became so popular. This system re- 
 quires a series of dry cells or a .storage battery, affording a low- 
 tension current and a timer, the current being stepped-up to a 
 high-tension by induction. The principle of self-induction is as 
 follows : 
 
 A current flowing through a coil of wire will set up a mag- 
 netic field in the surrounding space, but when the current is 
 stopped the magnetic field will stop. The effect of the stoppage 
 of the flow of current in this coil is the same as that due to the 
 change of position of the wire coil in a magnetic field, so that 
 when the current is stopped there will be a current induced in the 
 
74 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 coil. The result is that when the circuit is broken to stop the cur- 
 rent, the decrease in the current adds momentarily to the electro- 
 motive action in the circuit and a visible spark, or even an arc, 
 is formed at the break. 
 
 Fig. 54 makes clear the principles of an induction coil, show- 
 ing the primary and secondary circuits and the other components 
 of the system. 
 
 The primary and secondary windings are identical with those 
 of the compound armature, or high-tension magneto, the former 
 consisting of a small number of turns of coarse insulated wire, 
 while the latter is a very fine silk insulated wire, and the number 
 of turns greatly exceeds those of the primary winding. In this 
 system no mechanically operated interrupter is used for breaking 
 the primary circuit, this being accomplished by a device for 
 automatically and rapidly making and breaking the circuit. 
 
 The device is known as a vibrator or trembler, as it is some- 
 times termed, and consists of an iron disc of approximately the 
 same diameter as the core of the coil, attached to flat spring and 
 a platinum point located above the disc. An adjusting screw 
 mounted above the disc carries another platinum point. These 
 points are so situated on the coil that they make contact with each 
 other. When these two points are in contact, the primary circuit 
 is closed. 
 
 The automatic action of this vibrator is as follows: The cur- 
 rent flowing through the primary circuit of the coil makes an 
 electromagnet of the core, which attracts the iron disc attached to 
 the vibrator spring, causing the points to separate. As the cur- 
 rent is interrupted by the separation of these points, the core 
 ceases to be an electromagnet, since no current is flowing through 
 it and the disc is no longer attracted permitting the points to 
 make contact and again complete the primary circuit. This 
 action continues as long as the current flows and is interrupted 
 in the primary circuit. By varying the adjustment of the ad- 
 justing screws the number of sparks in a given time are varied, 
 as is also the strength of the individual sparks. 
 
 To prevent prolonging the magnetization of the core beyond 
 the desired limit, a condenser is connected with the contact 
 points to absorb the surplus current induced in the primary cir- 
 cuit, due to the breaking of the circuit. In other words, when 
 the points are in contact, the condenser is short circuited, but 
 when the circuit is broken the induced current, instead of jump- 
 ing across the gap, passes into the condenser, and as the circuit is 
 
IGNITION SYSTEMS 
 
 75 
 
 again completed it passes out again and into the circuit. A com- 
 mutator, or timer, is used to determine the exact time in the cycle 
 of the engine at which ignition occurs. 
 
 The diagram shown herewith represents a single-cylinder sys- 
 tem, while multi-cylinder engines require a coil for each cylinder, 
 but the battery current passing into the primary winding of the 
 coils is controlled by a single switch. The coil units are incor- 
 porated in a box or housing which is mounted on the dash board, 
 with a removable cover, so that any coil may be adjusted. As 
 each coil is a separate unit, they may be so constructed that they 
 may easily be replaced should they become defective, without 
 disturbing any connections. 
 
 In every high-tension battery system a device is required for 
 opening and closing the primary circuit at the proper instant, 
 with respect to the cycle of the engine, and the position of the 
 piston in the cylinder. This device is known as the timer, be- 
 cause it determines the exact time in the cycle of the engine at 
 which ignition occurs and permits of varying this point at will 
 while the engine is in operation. It is positively driven by gears 
 from the motor either direct or through an auxiliary shaft from 
 the cam shaft. This timer 
 (Fig. 55) consists of a hous- 
 ing containing a roller and 
 arm members so mounted upon 
 the driving shaft that the 
 roller and arm members may 
 rotate, while the housing is 
 held stationary by means of a 
 rod or lever, which may be 
 moved in either direction to 
 advance or retard the spark. 
 Within the housing is a fiber 
 ring in which are mounted 
 metal contact segments, the 
 surfaces of which are flush 
 with the fiber. 
 
 These segments are held in position by screw bolts which pass 
 through the fiber ring and housing, but are insulated from the 
 latter. These screw bolts are provided with thumb nuts and ter- 
 minals to which is secured a primary wire, which in turn is con- 
 nected to the primary terminal of the induction coil. 
 
 FIG. 55. Timer for Battery System. 
 
76 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 The operation of the timer is as follows : The shaft actuating 
 the roller is metal, and one lead from the battery is connected to 
 the frame, or other metal part, and the current is conducted from 
 its source to the metal segment. As the roller makes contact with 
 the segment in the fiber ring, the circuit is closed and the current 
 flows through the roller frame and primary wire back to its orig- 
 inal source. As the roller contact with the segment is broken, the 
 primary current in the coil is established and broken as pre- 
 viously described, being built up in the secondary winding, and 
 a spark produced at the gap of the spark plug electrodes. 
 
 The vibrator coil system has its disadvantages, having sev- 
 eral primary contacts, sliding or rolling contacts in the timer, 
 and a delicate, magnetic interrupter. To overcome these faults, 
 igniters were introduced which combine a mechanical interrupter 
 with a high-tension distributor. The induction coil is replaced 
 by a transformer coil, as used with the primary armature type of 
 magneto. With the igniter system but one primary contact is 
 necessary and the circuit is made and broken positively by me- 
 chanical means. 
 
 The contact points are generally so constructed that they 
 may be adjusted from the outside without dismantling the unit. 
 
 Directly above the contact maker is located the high-tension 
 distributor. Its construction is similar to the high-tension mag- 
 neto distributor, using a central contact brush and segments 
 located radially which are connected with the spark plugs of the 
 motor. 
 
 The advantages of this system over the vibrator coil system 
 are two-fold. As there is only one set of wearing parts, whatever 
 wear occurs will affect the timing of all cylinders equally and 
 subsequently a perfect relationship is maintained at all times. 
 Again the character of the spark in all cylinders must be identical. 
 
 Fig. 56 indicates the path of the current in the igniter system, 
 passing from the battery to the switch on 'the coil, thence to the 
 interrupter, from where it is led to the coil and stepped-up to a 
 high pressure. From the coil it passes through a conductor to 
 the central contact of the distributor and is distributed to the 
 cylinders in proper sequence. 
 
 Either the vibrator and timer system, or the igniter system, 
 may be used in connection with either the primary or compound 
 armature magneto, thus forming two separate systems of ignition, 
 with either one or two sets of spark plugs. With the former type 
 the magneto distributor is used for both systems, while a vibrator 
 
IGNITION SYSTEMS 
 
 77 
 
 and a transformer coil are mounted together and controlled by a 
 single switch. When the compound armature magneto is used, 
 but one coil is necessary for the battery system. The above is 
 also true of the igniter and transformed coil, excepting, of course, 
 that but one coil is necessary for either type of magneto. 
 
 To Coil- 
 
 FIG. 56. Indicating the Path of Current in an Igniter System. 
 
 Inductor Magnetos. The magnetos described previously, gen- 
 erating either high or low-tension current, were built on the prin- 
 ciple of placing the winding or windings on the armature core, 
 so as to rotate in unison with the armature. 
 
 The inductor type of magneto differs from the above, in that 
 the windings are stationary within the magnetic field of the mag- 
 neto and the armature is replaced by inductors which revolve, 
 being attached to a shaft. In fact, these are the distinguishing 
 features of this type of magneto. In other words, a stationary 
 winding is used and mechanical energy is transformed into elec- 
 trical energy through a distinctive principle known as induction. 
 
 This inductor type, like the primary and compound arma- 
 ture types, consists of permanent inverted U-magnets and pole 
 pieces which form the magnetic field, mounted upon a non- 
 metallic base. The winding or windings may be arranged for 
 
78 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 either a high or low-tension current and may either be placed in 
 the magnetic field or at the rear end of the magneto. 
 
 The armature is replaced by inductors, mounted upon a shaft, 
 this unit being termed the rotor shaft. The inductors are 
 in some cases fan-shaped. The Eemy inductor shaft, which is 
 
 of this type, is illustrated 
 in Fig. 57. It is made of 
 laminated steel, claim being 
 made for a better magnetic 
 circuit with this construc- 
 ts! wHif tion. Each lamination is 
 
 Ja *^S' ^^^^^Ht^^^^MV^KlB^te6 
 
 xf given an insulated coating 
 
 on one side, the object of 
 this being to eliminate eddy 
 FIG. 57. Eemy Induction Shaft. currents and to reduce heat 
 
 losses. 
 
 The circuit breaker, or interrupter, is also used to open and 
 close the primary circuit at the proper time, while the distributor 
 is also resorted to to distribute the high-tension current to the 
 proper cylinders. In fact, this type of magneto incorporates all 
 the principal parts mentioned in connection with the previous 
 types, such as the condenser, safety spark gap and switch. 
 
 The functions performed by these units are identical with 
 those described previously. As mentioned above, the principal 
 difference of this instrument over the others, lies in the method 
 of generating the current. 
 
 Previously the method of magnetizing a bar was described in 
 connection with the induction coil, and we may now investigate 
 the method of utilizing this magnetism to produce electrical 
 currents. 
 
 In a coil, an electrical current will be said to be flowing in the 
 coil, meaning that it passes in the wire. Magnetic flux, however, 
 will be said to pass through the core in either direction, the core 
 serving as a path to direct the magnetism through the coil. An 
 electrical action is produced by the action of the magnetism in 
 the core only when the strength of the magnetism varies, that is, 
 when it increases or decreases. When this is the case an electro- 
 motive force is induced in the winding and, the more rapid the 
 variation of the magnetism, the greater the induced electro- 
 motive force. Even if the core is traversed by a large amount of 
 magnetism, it has no effect on the winding, as long as its value is 
 
IGNITION SYSTEMS 
 
 79 
 
 unchanged. Electromotive force tends to produce an electric cur- 
 rent and if the circuit is closed it actually does produce a current. 
 The electromotive force produced in a single turn of winding 
 is proportional to the rate at which the magnetism through that 
 turn varies. A winding of several turns may be regarded as sev- 
 eral windings of one turn, connected in series, so that to obtain a 
 high induced electromotive force, a winding of several turns is 
 used, just as several dry cells are connected in series to obtain a 
 higher electromotive force from that obtained from a single cell. 
 
 FIG. 58. Positions of Inductors and their Shaft. 
 
 In Fig. 58 are shown various positions of the inductors and 
 their shaft. The upper view depicts the magneto with end plates 
 removed, and the lower view represents a section of the upper 
 view. 
 
 The stationary winding is securely held in place by the pres- 
 sure of the pole pieces against it and by brass strips which have 
 been omitted to simplify the illustration. The rear inductor, 
 which is located to the rear of the winding, is indicated by dotted 
 lines in the upper views. The inductors and core are secured to 
 the shaft and rotate with it, constituting the only moving parts 
 shown. 
 
 In order to form a path for the magnetic flux it is merely nec- 
 essary to have a mass of iron joining the pole pieces, this being 
 
80 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 provided by the inductors, core and their shaft. The arrows 
 show the path of the magnetism through the revolving parts. 
 
 In the position J., the front inductor is adjacent to the pole 
 piece N) the rear inductor is adjacent to the pole piece $, and the 
 path is formed by the inductor shaft. When the cross-section of 
 the inductor shaft is not great enough to carry all the flux, a 
 core must be added to carry part of it. The magnetism, there- 
 fore, in position J., passes from the pole piece N, to the front in- 
 ductor, through the core and shaft to the rear inductor, thence to 
 the pole piece S. The magnetism through the winding is from 
 the front to the back. 
 
 At B, the inductors are so located that each forms a path be- 
 tween pole pieces N and $, and the magnetism passes between 
 the pole pieces without any of it passing through the winding. 
 
 At 6 y , the conditions are similar to those at J., but the front 
 inductor is adjacent to the pole piece S and the rear one adjacent 
 to the pole piece N, causing the magnetism to pass through the 
 winding from back to front, which is opposite to the direction 
 which it had in position A. 
 
 Position D is similar to B, except that the front inductor is 
 downward and the rear inductor upward. In this position no 
 magnetism passes through the winding. From the above it can 
 be seen that the magnetism passing through the winding is con- 
 tinually varying, thereby inducing in the winding an electro- 
 motive force. 
 
 As the inductors approach position J., the magnetism through 
 the winding is increasing and as they leave that position the mag- 
 netism begins to decrease, without changing its direction. The 
 direction of the induced electromotive force is reversed as the in- 
 ductors pass through position J., and is again reversed when they 
 pass through position C. As the inductors approach position B, 
 the magnetism through the winding is from front to back and 
 decreasing, but after they have passed this position, it is from 
 back to front and increasing, resulting in no reversal of the elec- 
 tromotive force. This is also true of position D. 
 
 Although the current from an inductor magneto may be util- 
 ized in the same manner as that from any other alternating cur- 
 rent magneto, the above sets forth the conditions existing in the 
 Remy magneto. This instrument generates a low-tension current 
 and requires an outside coil to step up the current to the high 
 potential required at the spark plugs. 
 
IGNITION SYSTEMS 
 
 81 
 
 FIG. 59. K.W. Inductor Shaft. 
 
 In the K.W. inductor type of magneto (Figs. 59 and 60) 
 there are four inductors as illustrated made of soft iron lamina- 
 tions. Two of these inductors are placed 180 degrees to each 
 other and the other two in 
 a plane at right angles. 
 
 The windings, which are 
 concentric with the in- 
 ductor shafts are mounted 
 between the inductors and 
 stand absolutely still. The 
 inductors collect the mag- 
 netism from one pole piece 
 and conduct it through the 
 center of the windings to 
 the opposite pole piece. The 
 primary winding is sur- 
 rounded by the secondary 
 winding. The primary cur- 
 rent passes through the cir- 
 cuit breaker and at the moment of interruption a powerful surge 
 of current is generated in the secondary winding, which is dis- 
 tributed to the spark plugs, thus producing a high-tension current 
 without the aid of external coils. This is one type of inductor 
 magneto generating a high-tension current. The Pittsfield mag- 
 neto (Fig. 61) offers an- 
 other example of a high- 
 tension inductor type mag- 
 neto; however, it differs 
 materially from the above. 
 The usual primary and sec- 
 ondary windings are used, 
 however, they are not incor- 
 porated with the inductor 
 shaft, but are located at the 
 
 FIG. 60. K.W. High-Tension Inductor rear f the magneto. 
 
 Magneto. The three illustrations 
 
 show a longitudinal section 
 
 through the entire instrument, cross section through the magneto 
 and pole pieces and end view of the interrupter. 
 
 The magnetic field contains four poles, two (4A) of which 
 are the poles of the permanent magnet as illustrated, the other 
 7 
 
82 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 two poles (4) and the iron core (5) of the coil compose the field. 
 The rotation of the inductor shaft (1) generates in the windings 
 of the coil (6) an alternating current which attains a maximum 
 four times during each revolution of the inductor shaft, which 
 means, that for each 90 degrees rotation of the inductor shaft, 
 ignition may be obtained. One end of the primary winding is 
 
 23 
 
 FIG. 61. Longitudinal Sectional, Cross-Section and End Views of Pitts- 
 field Magneto. 
 
 connected to the field by a contact (8) and its other end is at- 
 tached to a contact block (9) which is screwed on the field and 
 insulated by a hard rubber bushing and plate. Connection from 
 this plate to platinum contact block (9) and screw is made by a 
 brass contact strip. The latter is insulated from the interrupter 
 plate (11), which is in metallic connection with the field or 
 ground. 
 
 The platinum screw (IS) on the interrupter lever (12) is held 
 against the platinum screw (1) in the insulated block by means 
 of a spring (H). The current generated in the primary winding 
 is therefore short circuited as long as the two platinum screws 
 are in contact. 
 
 The primary current is interrupted when the core (15) actu- 
 ates the lever (12) separating the platinum points. A condenser 
 (16) protected by a housing (17) is connected in parallel to the 
 interruption of the platinum points. One end of the secondary 
 winding is connected to one end of the primary winding and 
 the other is led to a conductor by means of a metal bridge (19). 
 The secondary current is led from this bridge member to the dis- 
 tributor (23) by means of insulated conductors (18), which are 
 connected by means of a carbon brush and spring. In the dis- 
 tributor plate (23) are socket inserts connected to distributing 
 
IGNITION SYSTEMS 83 
 
 inserts which take the high-tension current from the revolving 
 conductor (21} in proper rotation and from socket inserts in the 
 distributor plate (23) cables are connected to the spark plugs in 
 the cylinders. 
 
 The safety spark gap consists of a short pointed brass rod 
 set on the metal bridge (19) connecting the high-tension terminal 
 (26) on the coil (6) with the high-tension conductor bar (18), 
 and should there be any interference with the circuit normally 
 provided through the spark plugs, the safety gap provides a point 
 of discharge. 
 
 The timing of the spark is generally accomplished by opening 
 the interrupter earlier or later, and with the unavoidable result 
 that if the position of the pole pieces in the magnetic field re- 
 mains stationary, the relative position of inductor shaft and field 
 at the moment of the break must vary. The quality of the spark, 
 or, in other words, the heat value, depends among other factors 
 upon the particular position of the inductors in relation to the 
 field poles at the moment the spark is produced. 
 
 The changing of the timing is effected in the Pittsfield mag- 
 neto in a unique way. The results obtained are ideal in that the 
 same efficient spark is obtained, when the spark is either ad- 
 vanced, retarded or in any intermediate position. This is accom- 
 plished by means of a four-segment sleeve (no. 27), one for each 
 pole of the machine, which sleeve is fitted with a lever with which 
 the sleeve, with interrupter, can be advanced or retarded, giving 
 early or late ignition. 
 
 The inductor type of magneto is also made in the dual type; 
 in fact, in the Remy, the same transformer coil, interrupter and 
 distributor as is used for the magneto current. With the K.W. 
 it is necessary to employ an external coil. 
 
 The Pittsfield dual system is somewhat different from the 
 other types explained, and owing to the unique construction it 
 is very simple. It does away with the high-tension coil and wires 
 from the magneto to the switch, the dual system being self- 
 contained. 
 
 The design and constructional details of the dual machine 
 differ from the independent type, as previously described, by 
 insulating both ends of the primary circuit instead of one end. 
 One end of the primary winding is connected to the interrupter 
 as in the independent type, the other to the lever of a specially 
 constructed switch, so that when the switch lever is on the side 
 
84 ' MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 marked " Magneto," this primary lead is grounded, allowing the 
 magneto to run as a straight high-tension machine. When the 
 lever is thrown to the battery side of the switch the primary lead 
 is then connected to the batteries, thus permitting the primary 
 and secondary windings of the magneto to be used for either 
 current. 
 
CHAPTER VI 
 
 GOVERNORS AND SPEED-CONTROLLING DEVICES 
 
 COMMERCIAL car manufacturers and users are aware of the 
 attendant results of high speeds and heavy loads over rough 
 roads, so that at the present time this subject should be of con- 
 siderable interest to those operating commercial cars. 
 
 The most practical means of obviating this excessive speed 
 seems to be through the use of a governor, which should be sealed 
 so that it cannot be tampered with. 
 
 This governor consists of a mechanical speed-measuring de- 
 vice so connected to the engine throttle as to cut off the intake 
 when the speed exceeds a predetermined maximum. It was orig- 
 inally inherited from steam engine practice. However, lately, 
 considerable improvements have been made in this device so as to 
 make it more adaptable and efficient. 
 
 There are four methods of regulating the speed of the motor, 
 as follows: (1) By holding the exhaust valve open or the intake 
 closed, (2) by the spark, (3) by changing the quality of the mix- 
 ture entering the cylinder, (4) by changing the quantity of the 
 mixture entering the cylinder. 
 
 The method of regulating the motor speed through connecting 
 the governor to the exhaust valves in such a way that these valves 
 may be held open, and thereby retard the speed of the motors, or 
 by connecting to the intake valves in such a way that they may 
 be held closed, has been discarded long ago. 
 
 The Dedion Bouton method of regulating the motor speed 
 through connecting the governor in such a way that it will open 
 and close the electrical circuit, has also been discarded. This 
 also applies to the method of changing the quality of the mixture 
 entering the cylinders. 
 
 One method of governing the speed of the motor is by con- 
 necting the governor to a butterfly valve in the intake manifold, 
 which reduces the quantity of the mixture entering the cylinder 
 but does not in any way reduce the quality. The butterfly valve 
 merely changes the volume of gas and allows the motor to get 
 the proper mixture under any speed up to the setting of the 
 governor. 
 
 85 
 
86 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 The revolving ball, or more properly the centrifugal prin- 
 ciple, is that generally employed. There are many variations of 
 this construction and few that operate on different principles, but 
 all are alike in fundamentals. 
 
 The hydraulic principle is also used by some. In this type, 
 as the motor speed raises the pressure against a diaphragm con- 
 nected with a plunger-head acting on the throttle spring. This 
 action overcomes the resistance of the spring and closes the 
 throttle. This type may either be built in a unit with the pump 
 or connected to it. 
 
 There is also the automatic type which regulates the motor 
 speed by governing the velocity of the incoming gases. 
 
 There are two methods of drive for the centrifugal type of 
 governor. The usual method is direct from the engine, either 
 through an auxiliary shaft, or by building the governor into the 
 cam-shaft gear. With this method the speed of the governor is 
 always proportioned to the speed of the motor. 
 
 Lately governors are being introduced which are driven from 
 some part of the chassis and whose speed is proportioned to the 
 speed of the vehicle instead of the motor. 
 
 In the former case the governor acts only on the motor and 
 converts it into practically a constant speed motor. In changing 
 speeds the allowed speed of the motor is in no wise altered. 
 
 The governor is generaly set at a maximum speed correspond- 
 ing to the maximum car speed at which the car is to operate on 
 high gear, and when it is running in second speed the effect of 
 the governor on the motor does not change in any way. This 
 second speed might correspond to 12 m.p.h., and the low speed to 
 6 m.p.h., thus limiting the motor speed on the lower gears, hence 
 the power of the motor. This would be quite noticeable if the car 
 was operated over a long stretch of bad road or in deep sand. 
 The power output of the engine is dependent upon its speed and 
 although it may be pulling hard on a wide open throttle, it is not 
 developing its full power, for not enough power units are re- 
 leased from the fuel, owing to the limited speed. The maximum 
 safe motor speed may be far above the speed permitted by gov- 
 ernor for a given car speed. 
 
 These defects c have caused engineers to investigate other 
 methods of governor drives and has resulted in the introduction 
 of a transmission jack shaft or front-wheel drive, on the theory 
 that the speed of the motor should be governed by the speed of 
 the car. In this way the truck can attain its maximum speed at 
 
SPEED-CONTEOLLING DEVICES 
 
 87 
 
 a moderate engine speed, and with only a partly opened throttle. 
 It also permits the motor to operate at a higher speed on the 
 lower car speeds. In practice with the proper size motor for a 
 certain car capacity, the gear ratio is generally such that the 
 maximum safe motor speed is reached in second speed, so that the 
 maximum power may be obtained when it is most necessary. The 
 motor should not be permitted to develop its full power in high 
 gear, as gear changes are provided to obtain increasing torque 
 with decreasing car speed. Limiting the motor power in high 
 speed is an advantage up to a certain point, for a truck should 
 never be permitted to take a hill on high gear if it is necessary to 
 retard the spark all the way. 
 
 MECHANISM 
 
 SECTION of GOVERNOR 
 GEARS 
 
 FIG. 62. Centrifugal Type of Governor. 
 
 There is also a governor on the market at the present time 
 which controls both the motor speed and the car speed, the 
 object of this device being to obtain a better fuel economy and 
 to form an assistance to the driver in operating the vehicle. 
 
 While still another automatic governor in addition to con- 
 trolling the speed also operates the throttle and spark and con- 
 
88 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 trols the motor under all speeds. The operator merely sets the 
 governor as to the speed he wishes to make and the governor does 
 the rest. 
 
 The writer is attempting to cover this subject in such a way 
 as to present all types of governors now in use and those which 
 may come into general use. 
 
 The Centrifugal Type. Fig. 62 illustrates a centrifugal type 
 of governor which has been used by a number of prominent com- 
 
 WATER 
 CHAMBER 
 
 FIG. 63. Hydraulic Type of Governor. 
 
 mercial car builders. The governor is placed at the front end of 
 the motor and is driven through spiral gears from the magneto 
 drive shaft. As the motor speed increases the weighted levers 
 open and raise a sleeve which operates the auxiliary throttle 
 valve in the intake manifolds, by means of a forked lever bearing 
 in the sleeve and a flexible shaft which operates a rack meshing 
 with a small gear on the auxiliary valve shaft. As the speed de- 
 
SPEED-CONTROLLING DEVICES 
 
 89 
 
 creases the pressure of the governor spring returns the operating 
 parts to their neutral position. 
 
 The Hydraulic Type. Fig. 63 shows a hydraulic type of gov- 
 ernor used by some commercial car builders. It is mounted be- 
 tween the intake manifold and the carburetor. The operating 
 mechanism is combined in a unit with the governor proper, mak- 
 ing it a simple -and compact unit. The water chamber is con- 
 nected with the water pump and as the latter's speed increases, 
 the water pressure raises and forces the diaphragm down. This 
 diaphragm has a stem which bears on the throttle lever and is 
 controlled by a coiled wire spring. The lever in turn forms a 
 segment with several teeth and meshes with a small gear on the 
 throttle valve shaft. As the pressure decreases the spring re- 
 turns the diaphragm to its original setting and opens the throttle 
 valve. The water chamber cover, operating lever housing and 
 the spring retaining plug are sealed so that the governor cannot 
 be tampered with, without first breaking either one of the three 
 seals. 
 
 In both of the above types the maximum speed may be 
 changed by increasing or decreasing the spring tension. 
 
 The Automatic Type. An automatic type of governor is 
 shown in Fig. 64, in which the speed is regulated by governing 
 
 DISC 
 
 SPRING 
 
 CONTROLLi 
 
 THSDISC 
 
 FIG. 64. Automatic-Type GoverDor. 
 
 the velocity of the inflowing gases. This device consists of a 
 throttle connected to a disc that is allowed to float under a con- 
 stant spring tension, in a tapered conduit, the tension of the 
 spring determining the maximum engine speed. The slightest 
 change in the velocity of the incoming gases caused by a dif- 
 
90 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 ference in engine speed will affect the position of the disc in the 
 conduit and also change the position of the throttle immediately, 
 giving the engine more or less gas as the conditions may require. 
 An auxiliary control lever is provided, giving the operator access 
 to any engine speed under the maximum controlled by the gov- 
 ernor. This governor is designed to be mounted between the 
 intake manifold and the carburetor and does not require any 
 form of drive whatever, its operating mechanism being self- 
 controlled. 
 
 The Krebs truck is equipped with a centrifugal type of gov- 
 ernor which controls the motor and car speed. The spark and 
 throttle are so connected to the governor that it constantly sets 
 them for the power, load and speed that may be required, without 
 
 FIG. 65. Another Type of Centrifugal Governor. 
 
 regard to road conditions. The governor is also so contrived that 
 when the clutch is disengaged, the motor continues to run at the 
 same speed, preventing the driver from racing the engine. En- 
 gaging the clutch causes the throttle to open wide until the car 
 reaches the speed at which the governor is set. The manufacturer 
 of this governor claims that it takes the entire responsibility of 
 handling the motor at all speeds and all loads. This governor is 
 shown in Fig. 65. 
 
 Fig. 66 illustrates the Pierce engine governor, which also 
 operates on the centrifugal principle. It differs from the above 
 in that it is designed to be mounted between the intake manifold 
 
SPEED-CONTEOLLING DEVICES 
 
 91 
 
 and the carburetor, making it more adaptable to motors in gen- 
 eral. The drive may either be taken from the cam shaft of the 
 motor or countershaft of the transmission. As the motor speed 
 
 FIG. 66. Pierce Centrifugal Type Governor and Drive. 
 
 reaches the maximum setting of the governor, the triangular 
 weights open and move endwise on the shaft upon which they 
 are mounted, which in turn moves the operating rod. The end 
 of this rod carries a rack gear which is in mesh with a small gear 
 on the butterfly valve shaft. As the weights close a spring re- 
 turns the rod to its neutral position. The governor also has a 
 speed adjustment, so that any desired motor speed may be ob- 
 tained. This adjustment is sealed so that it cannot be tampered 
 with. 
 
 Fig. 67 shows the Pierce speed controller which operates on 
 the same principles as the Pierce governor. The drive is taken 
 from the front wheel and is similar to a speedometer drive. It 
 is so constructed that it is impossible to remove the driving gear 
 without breaking the seals and removing the front wheel. The 
 triangular weights are placed at right angles to the valve op- 
 erating rod, the governor shaft movement being transmitted 
 through a bell crank. The controller is provided with a variable 
 speed dial, which changes 'the spring pressure on the operating 
 rod and permits f instant adjustment of speed to suit individual 
 requirements, automatically controlling vehicle speed, leaving the 
 motor free at all times. This controller may also be provided 
 with a lock so that it is impossible for any one to start the vehicle 
 without the key. 
 
 The housing of both devices are made of aluminum, so that a 
 minimum weight is carried by the intake manifold. The chief 
 advantage claimed for these devices, is their adaptability to any 
 vehicle, as it is only necessary to drop the carburetor one inch to 
 one and one-half inches. In case of repairs it is a very simple 
 
92 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 matter to remove the governor or controller entirely, raise the 
 carburetor and the vehicle need not be laid up pending the return 
 of either device. 
 
 THROTTLE VALVE- 
 
 RECULAT/NG 
 
 D/XL 
 
 FIG. 67. Pierce Centrifugal Governor. 
 
 The Duplex governor shown in Fig. 68 was designed on the 
 principle of a dual actuating influence. This dual influence con- 
 sists of a motor influence, as to its speed, which is imparted to the 
 governor, and a vehicle influence which is also imparted to the 
 governor. The motor speed is conveyed from some revolving 
 part of the motor to one of the speed terminals of the governor, 
 and the vehicle speed from the propeller shaft or jack shaft. The 
 conveying means consists of a steel cable revolving in a hard fiber 
 or metallic casing. The governor is so constructed that it may be 
 mounted between the intake manifold and the carburetor. In- 
 
SPEED-CONTKOLLING DEVICES 
 
 93 
 
 stead of the ordinary butterfly valve a grid valve is used, through 
 which the entire gas supply must pass. This grid valve consists 
 of a fixed part set into the upper part of the valve chamber, 
 which is provided with a series of elongated slots, with flaring 
 walls from its upper surface downward. When the openings of 
 
 FIG. 68. The Duplex Governor. 
 
 both fixed and movable parts coincide, the valve is open and when 
 the bars of one part cover the openings of the other part, the 
 valve is closed. The movable part is held open by spring tension 
 and its possible motion in either direction is limited by adjusting 
 screws. 
 
 Within the governor there are two automatically acting one- 
 way clutches, the floating members of which consist of gears in 
 mesh with a third gear mounted on the centrifugal governor 
 spindle. These clutches are so designed as to impart to the cen- 
 trifugal member that of the two speeds which is the higher. With 
 the motor running idle, the motor speed will actuate the governor, 
 and the motor is always under governor control. When the 
 vehicle is propelled by the motor on the higher gears, the speed 
 imparted to the governor by the vehicle will be the higher speed 
 and will govern the motor, -whereas on the low gears the motor 
 speed will be the higher and will govern the motor. 
 
 The influence of the centrifugal member, as a result of the 
 speeds imparted to it, is to develop a pressure sufficient to over- 
 come the spring pressure tending to hold the valve open, and to 
 close it. As soon as the pressure is removed, the movable valve 
 part is released and returned to its full open position. Provision 
 
94 MOTOK TEUCK DESIGN AND CONSTRUCTION 
 
 is made for adjustment, which is enclosed and provided with a 
 lock so that it cannot be tampered with. 
 
 These various types of governors have their advantages and 
 disadvantages, while there may also be certain disadvantages to 
 their omission. When commercial vehicles are not equipped with 
 governors, the owner is forced to rely entirely upon the discretion 
 of the operator, while the manufacturer must rely on careful 
 management of them by the owners to prevent the evils of motor 
 racing and excessive speed. This also applies on hills where it is 
 asserted that governors are of no use in preventing excessive 
 vehicle speeds. 
 
 There are some who claim that there is no adequate method 
 yet devised which is capable of governing a truck or its engine, 
 without handicapping the driver somewhat in the operation of 
 the vehicle. However, the writer opines that it is worth while 
 fool-proofing the commercial car even in a crude way, particu- 
 larly in speed. With solid tires and the tendency to overload 
 commercial vehicles, the speed becomes a large factor in obtain- 
 ing long life. 
 
 It may be said that certain governing devices do limit the 
 power of the motor on the lower car speeds. However, this may 
 not be as serious as some think, as these vehicles are operated on 
 the higher speed the greater portion of the time. 
 
 Some also claim that the intelligence and general ability of 
 the commercial vehicle operator exceeds that of the touring car 
 operator, but as the conditions of both are vastly different, it is a 
 difficult matter to determine this fact. Truck drivers as a rule 
 are paid a certain wage for a stipulated number of hours per 
 week, and if they are delayed long enough in their daily trips 
 to make their work exceed this stipulated time, they will try and 
 make up this discrepancy by speeding up the vehicle whether 
 loaded or empty. 
 
 However, it should be remembered that there is a certain class 
 of conservative operators who can operate a vehicle safely with- 
 out limiting its speed, but as operators of this class are few, some 
 means must be resorted to for limiting the destruction of trucks 
 through excessive speeding. 
 
 Many manufacturers equip their vehicles with governors ad- 
 mitting their shortcomings, arguing that even though the econ- 
 omy and efficiency of the truck may be slightly affected, this loss 
 is more than made up for by the saving in depreciation resulting 
 from the unskilful operation of careless drivers. 
 
CHAPTER VII 
 
 THE CLUTCH AND TRANSMISSION 
 
 THE defects in the gasoline engine, relative to its flexibility, 
 have been previously mentioned. Among these is the inability 
 of the motor to develop its full torque from a standstill. The 
 crank shaft of the motor must rotate at a speed consistent with 
 power requirements, while the road wheels must rotate consistent 
 with road conditions, or as the operator wills. For this reason it 
 becomes necessary to use a transmission. The motor must be 
 started by a hand crank, or some starting device, which only pro- 
 duces enough torque to just turn the motor over against compres- 
 sion, so that it becomes necessary to disconnect the motor from 
 the other driving units of the vehicle for starting and after the 
 motor has attained its speed to connect it with the vehicle again. 
 
 For this purpose a device must be used, which will allow a 
 certain amount of slippage until the motor speed has been re- 
 duced and the vehicle speed gradually accelerated to such a point 
 that the two correspond, in this way preventing shock and jar to 
 the driving mechanism. 
 
 This feature is accomplished by the clutch, which is most gen- 
 erally placed in close proximity to the motor. The most popular 
 position is inside the flywheel. In commercial cars a single clutch 
 is generally employed, which serves to connect the engine to the 
 driving wheels through all of the different gear reductions. It is 
 normally held in engagement by a single spring of large diam- 
 eter, or by a number of smaller springs, and is controlled by a 
 foot pedal to disconnect it from the motor by releasing the fric- 
 tion surfaces, thus disconnecting the power of the motor from 
 the driving units. When it is desired to disconnect the engine in 
 order to stop the car, or to change the gear, the clutch is first dis- 
 engaged by foot pressure upon the pedal, which compresses the 
 spring; the gear is then disengaged or changed and the clutch 
 let in again. 
 
 There are quite a number of different types of clutches, all 
 more or less extensively used, as follows : Conical clutches of the 
 indirect or direct type, multiple disc clutches, dry plate clutches, 
 band clutches, and combinations of cone and disc type. The 
 
 95 
 
96 MOTOK TKUCK DESIGN AND CONSTRUCTION 
 
 construction of each type varies considerably in details of design 
 and the materials used for the frictional surfaces. 
 
 In light commercial cars of 4,000-lbs. capacity, or under, 
 there is a tendency to use the unit power plant, in which the 
 motor, clutch and transmission are always held in alignment, 
 while on the heavier types the transmission and jack shaft are 
 combined in a unit or mounted amidships for shaft drive. With 
 the latter types it is necessary to use a double universal joint be- 
 tween the clutch and transmission units. The universals take up 
 any misalignment due to frame weaving. In some cases they are 
 bolted to the clutch, spider or spigot, while in others they are 
 built into the clutch center. This latter construction seems to be 
 gaining favor with multiple disc clutches which operate in oil, 
 a portion of which is distributed to the universal, causing it to be 
 self-maintaining. 
 
 A variety of methods are resorted to for mounting the clutch 
 on the spigot, plain, ball and roller bearings being used for this 
 purpose. 
 
 There is also a tendency to provide clutch brakes so that the 
 tendency of spinning caused by the inertia may be reduced to 
 facilitate gear shifting. 
 
 Cone Types. Among the conical clutches we find two types 
 in general use, direct and indirect types. Either type consists of 
 a male and female member, the male member being forced into 
 the female member by the pressure of the spring or springs. 
 When one spring is used, it is attached to the clutch spigot and 
 when a number of small springs are used they are attached to a 
 spider, which is free to float on the clutch spigot. The action of 
 the clutch members is similar to a wedge movement. It is the 
 oldest type and also the simplest type in use at present. The fly- 
 wheel generally forms the female member for the direct type, 
 while the male member may either be made from aluminum or 
 pressed steel and covered with a material such as Raybestos, 
 leather, etc. In the indirect type it is necessary to bolt the female 
 member to the flywheel. The clutch spigot may either be an ex- 
 tension of the crank shaft or it may be bolted to the flywheel. 
 
 Fig. 69 serves to illustrate the general construction of the 
 direct type. The male member is provided with cork inserts to 
 obtain a higher coefficiency of friction and is bolted to a cast- 
 steel housing, which is mounted on the clutch spigot and sur- 
 rounds the clutch spring. The spigot is formed by an extension 
 of the crank shaft, and is provided with a thrust bearing. 
 
THE CLUTCH AND TRANSMISSION 
 
 97 
 
 The cone clutch, depicted in Fig. 70, differs from the above in 
 that three small springs are used. These small springs are sup- 
 ported on studs, which are riveted to the clutch spider. The 
 spider is provided with a die-cast babbitt bearing instead of a 
 
 PRESSED 
 
 STEEL 
 
 CONE 
 
 SPRING A NO 
 -PLUNGER 
 
 FIG. 69. General Construction of Direct FIG. 70. Cone Clutch with 
 Cone. Three Small Springs. 
 
 cast-bronze bearing. It depicts a type which is generally incor- 
 porated in the unit power plant, owing to its short length, .which 
 is a desirable feature. 
 
 An indirect type of cone clutch is shown in Fig. 71. The male 
 member is made of aluminum and is provided with a fractional 
 lining and cork inserts. Small pieces of rubber are placed under 
 the lining to obtain a smooth and gradual engagement. The 
 female member is made of gray iron arid bolted to the flywheel. 
 It also forms the retaining member. 
 
 The spigot is bolted to the flywheel and provided with a 
 
 bronze bearing, while a roller bearing is used as a thrust bearing, 
 
 and the disengaging collar is provided with a ball-thrust bearing. 
 
 Cone clutches of both types are also provided with flat springs, or 
 
 8 
 
98 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 plungers, and coil springs, which are placed under the fractional 
 facing, the object being to prevent the tendency to jerk when first 
 
 engaged. The friction ma- 
 terial is, in most cases, riv- 
 eted to the male member, 
 while in a few cases T-head 
 bolts are used to facilitate its 
 replacement, while one or two 
 makers rivet it to the female 
 member. 
 
 Multiple-disc Type. Multi- 
 ple disc and plate clutches are 
 based on the same principle as 
 the cone clutch, but constitute 
 in a sense extreme opposites in 
 design. This type offers sev- 
 eral advantages not found in 
 the others, being the most com- 
 pact. The required frictional 
 surface is obtained by a mul- 
 tiplicity of small surfaces, in 
 preference to two large ones, 
 as in the case of the cone and 
 plate types. 
 
 A disc clutch consists of two sets of discs, one set being termed 
 the driving discs and the other the driven discs. The driving 
 discs are generally provided with key slots on their outer circum- 
 ference, which fit over hardened steel keys riveted to the inside 
 circumference of the housing bolted to the flywheel. The driven 
 discs are also provided with key slots, but these are placed on 
 their inner circumference, which fit over keys riveted to a hous- 
 ing attached to the driven shaft. It is general practice to use one 
 more driving disc than there are driven discs, so that the two end 
 discs may be of the same kind. The driving set is driven by the 
 engine, while the remaining set is attached to a continuation of 
 the transmission shaft. In some cases small flat springs are used 
 to keep the discs apart under conditions where it is desired to 
 render the clutch inoperative, that is, when the spring pressure is 
 removed from them. 
 
 It is usual practice to enclose a clutch of this kind in an oil- 
 tight case, which insures that the members will operate in a con- 
 stant bath of oil, meaning long life of the frictional surface as 
 
 FIG. 71. Indirect Cone Type. 
 
THE CLUTCH AND TRANSMISSION 
 
 99 
 
 well as gradual engagement. Owing to its comparatively small 
 
 diameter, the inertia is not very great and gear shifting is some- 
 what easier than with the 
 
 cone clutch. The spring 
 
 pressure is great enough, so 
 
 that when engagement is 
 
 made the oil will be squeezed 
 
 from between the plates 
 
 and the frictional surfaces 
 
 brought into contact. As 
 
 the oil is gradually squeezed 
 
 out, and as there will be a 
 
 certain amount of slippage 
 
 as long as any considerable 
 
 amount of lubricant re- FIG. 72. Helle Shaw. Multiple-Disc 
 
 mains, the power will be Clutch. Universal Type. 
 
 applied gradually. 
 
 A multiple-disc clutch, which is ex- 
 tensively used in commercial cars in 
 this country and abroad, is the Hele- 
 Shaw clutch, illustrated in Fig. 72. 
 The discs are niade from steel and 
 bronze, with V-groove corrugations. 
 Only the walls of these grooves come 
 in contact and the remaining portions 
 of the disc serve to radiate the heat en- 
 gendered during slippage. To permit 
 the oil to enter and escape freely, these 
 discs have small holes drilled in the 
 inner walls of the grooves near the 
 peak. The action obtained by these 
 grooves is a wedge action similar to the 
 cone clutch. This also illustrates a de- 
 sign in which pressed steel is used 
 wherever it is possible to do so. The 
 clutch is of the universal type, having 
 an external and internal gear type of 
 
 universal, mounted inside of the clutch. A clutch brake is also 
 
 provided to facilitate gear shifting, this brake being mounted 
 
 upon the drive shaft and adjustable for wear. 
 
 Fig. 73 is a type of multiple-disc clutch used in connection 
 
 with unit power plants. It is built onto an extension of the 
 
 FIG. 73. Type of Mul- 
 tiple-Disc Clutch used in 
 Unit Power-Plants. 
 
100 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 transmission shaft, one end of which is supported by a ball bear- 
 ing in the flywheel. The frictional surfaces consist of saw-steel 
 driving discs and Raybestos-line, steel-driven discs. The con- 
 struction is similar to those described above, excepting that two 
 large springs are used, one being placed around the other and 
 retained by three bolts, which provide adjustment for the spring 
 tension. 
 
 The housing or driving member bolted to the flywheel has 
 teeth cut on its inner periphery into which the plates fit instead 
 of keys and the plates have teeth instead of key slots. 
 
 Dry-plate Type. The dry-plate clutch is similar to the mul- 
 tiple-disc type ; however, the discs are of a much larger diameter 
 
 FIG. 74. Bore & Beck Dry Plate Clutch. 
 
 and but three or five plates are necessary. The driving discs are 
 either Raybestos rings or bronze plates with cork inserts, while 
 
THE CLUTCH AND 
 
 the driven discs are made of steel. These clutches are not de- 
 signed to run in oil, but are liable to wear because of the amount 
 of contact surface provided. 
 
 A popular three-plate clutch of conventional design is shown 
 in Fig. 74. The face of the flywheel forms one surface, while a 
 moving member forms the other. Between them are two discs 
 of friction material and a floating member which is keyed to the 
 driving shaft. Pressure is obtained by coiled spring acting on a 
 sleeve which actuates the toggle mechanism operating the mov- 
 able member. This toggle mechanism is supported by a disc 
 which is bolted to the flange. This flange has two slots through 
 which the bolts pass and this together with taper surfaces on the 
 movable member form a means adjustment for wear of the fric- 
 tion discs. 
 
 In Fig. 81 is shown a simple plate clutch for low power de- 
 livery cars. This clutch is almost entirely of pressed steel and 
 utilized the flywheel as a driving member. Two additional driv- 
 ing plates are used and these are supported by three hardened 
 steel pins fastened to the flywheel, which also carry the springs. 
 The driven member consists of a spur gear which supports the 
 driven plates that have teeth cut on their inner periphery. 
 
 FIG. 75. Hilliard Clutch with Double Annular Ball Bearing and Enclosed 
 
 Spring. 
 
 The Hilliard clutch (Fig. 75) is another excellent example 
 of the plate type. Spinning of the rotating members is prevented 
 
102 MO f rDB^ TRtJK DESIGN AND CONSTRUCTION 
 
 by a combination of quick acting release, which does not permit 
 of a drag while releasing and further by having the parts so light 
 that rotation does not continue long. 
 
 Band Type. Band clutches are practically the same in gen- 
 eral principle of operation, as band brakes, and are of the same 
 general types, internal expanding and external contracting. This 
 type of clutch is not very popular, and but few can be found on 
 commercial cars at present. 
 
 There is a tendency on the part of manufacturers to use ball 
 bearings for supporting clutches of all types, as the plain bearing 
 is hard to lubricate effectively and the friction of same tends to 
 produce dragging. The ball bearing can be more easily lubri- 
 cated, requires less attention and eliminates this dragging evil. 
 
 Comparisons. The advantages of the cone clutch are that it 
 may be engaged and disengaged with very small axial motion, 
 axial pressure may be low because the normal pressure between 
 f rictional surfaces is multiplied by the angularity of the cone, its 
 weight is not very great as the male member may be made of 
 aluminum or pressed steel, its engagement is entirely independent 
 of speed and centrifugal force, no liquid lubricant is needed with 
 attending viscosity, drag and change due to wear and tem- 
 perature. Disengagement may, therefore, be made perfect. The 
 chief disadvantage of this clutch is its size, it being more bulky 
 than the other types with the possible exception of the dry-plate 
 type. Inertia is also a disadvantage, as this must be as small as 
 possible, in order to make gear shifting easy and to avoid gear 
 clattering. 
 
 These objections led to the introduction of the multiple-disc 
 clutch, in which the frictional surface can be made larger and the 
 f rictional force smaller per unit surface. The chief disadvantage 
 of multiple-disc clutch is its tendency to drag if the oil in the 
 clutch housing is not suitable for the purpose. Most makers 
 recommend a light machine or cylinder oil and kerosene. It can 
 readily be understood that the thinner the lubricant, the better 
 the clutch will hold, while the more viscous lubricant will permit 
 it to pick up its load more gradually. 
 
 To overcome the dragging evil, the dry disc type was intro- 
 duced. The surfaces are not lubricated but are most generally 
 provided with frictional facings in order to increase the co- 
 efficient of friction. This clutch has its disadvantages of inertia, 
 similar to the cone type. 
 
THE CLUTCH AND TKANSMISSION 103 
 
 The combination of dry plate and cone has the features of the 
 dry plate, its tendency to gradually pick up its load and the hold- 
 ing power of the cone after it has assumed its load. It is also 
 simple in construction. However, it requires frequent adjustment. 
 
 At the present time, the cone, multiple disc and plate clutches 
 are by far the most popular and seem to be holding their own, 
 with all the new types which are being experimented with. 
 
 The Transmission. In every gasoline engine it is absolutely 
 necessary that some method be used for changing the relation be- 
 tween the speed and power of the car. When a gasoline engine 
 is loaded above a certain limit it slows down, and the intervals 
 between the explosion in each cylinder become so far apart as to 
 cause the engine to labor and finally stop altogether, unless some 
 means is used to increase the speed of the engine by decreasing 
 the load upon it. In considering this subject it must be remem- 
 bered that, when a car is using its maximum power, it may be 
 divided either into considerable pulling power with slow speed, 
 or high speed with low pulling power. Consequently, when a car 
 is going at high speed and a considerable grade or a stretch of 
 heavy road is encountered, the car will begin to slow down until 
 the speed reaches such a point that the engine begins to knock 
 and labor. When this point is reached, it becomes necessary to 
 change to a slower gear, which, for the same speed of the 
 vehicle, gives a considerably greater number of revolutions of 
 the engine, with a consequently larger pulling power. 
 
 This pulling power is termed " torque," and if gasoline engines 
 could be designed as to afford an increasing torque, with decreas- 
 ing speed, all would be well and the transmission could be elim- 
 inated. As it is taking into account the power of the motor at 
 several speeds, nothing of this sort can be considered. At very 
 low speed torque becomes of greatest importance, and this is espe- 
 cially true in vehicle operation. 
 
 The use of the transmission is also necessary in starting the 
 vehicle, because until the vehicle reaches a certain momentum, 
 there is considerable load on the engine, so that a slow speed 
 which allows a high number of revolutions of the motor must be 
 used. 
 
 It is generally understood that to reverse the motion of 
 the commercial car engine is to labor under disadvantages in 
 numerous ways. Power will be lost, owing to the inferior valve 
 timing relation which must follow if the cam shaft was designed 
 
104 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 to suit reversing condition. Unless certain complications were 
 introduced in the valve action, and since in any case it would be 
 necessary to add to the flexibility of the motor by the use of a 
 transmission, it would seem unnecessary to add to the valve 
 motion anything by the way of complicated devices. An addi- 
 tion to the gear set is less complicated and the end is adequately 
 served. 
 
 Types. The most popular transmissions are the friction, 
 planetary and sliding gear. The friction and planetary, with 
 few exceptions, are only used on the light vehicles, while the slid- 
 ing gear type is extensively used on all sizes of vehicles. 
 
 Friction Type. There are two types of friction transmission 
 in use at the present writing, the single disc and the double disc. 
 This single-disc type consists of a driving disc which is attached 
 to the flywheel or an extension of the crank shaft, and always 
 rotates with it and a driven disc which can be slid along a cross 
 
 shaft and brought into 
 f rictional engagement with 
 the driving disc. By mov- 
 ing the driven disc out 
 from the center of the 
 driving disc the speed can 
 be varied from nothing 
 to maximum, and by slid- 
 ing it to the opposite side 
 the direction of motion is 
 reversed. Before the 
 wheel is slid in the direc- 
 tion of its axis it must be 
 disengaged from the driv- 
 ing disc. This is accom- 
 plished by either moving the cross shaft and its bearings or by 
 moving the driven disc. From this cross shaft the final drive may 
 be through a single chain to the rear axle, or it may be through 
 a single chain to the jack shaft and then through double side 
 chains to the road wheels. Fig. 76 illustrates a friction trans- 
 mission of the single-disc type. The discs are shown in the high 
 position, while the lower speeds are obtained by moving the 
 driven disc in towards the center, and reverse is obtained by mov- 
 ing the driven disc toward the opposite side of center. 
 
 Planetary Type. The planetary transmission is somewhat 
 cheaper to manufacture than the sliding gear type and also re- 
 
 FIG. 76. 
 
 Single-Disc Friction-Type 
 Transmission. 
 
THE CLUTCH AND TRANSMISSION 
 
 105 
 
 quires less skill in operation. There are two types of planetary 
 gears, those comprising internal gears and those comprising only 
 spur gears in their makeup. The latter is the most popular type 
 and will be considered. 
 
 Fig. 77 depicts this type of transmission, and its principle of 
 operation may be described as follows : 
 
 FIG. 77. Planetary Transmission with Spur Gears. 
 
 The driving shaft A carries the driving pinion B, which 
 meshes with the planetary pinion G. The latter forms part of 
 sets of three pinions which are formed integral. D is the low- 
 speed planetary pinion meshing with the low-speed gear E which 
 is secured to the driven shaft F. By applying the brake band G 
 to the combined pinion carrier and drum H, the planetary pin- 
 ions are held stationary in space and act like a back gear. Pinion 
 B rotating in a right-hand direction (see end diagram), turns 
 pinions G and D on their pin M in a left-hand direction, and 
 pinion D turns gear E and the driver shaft F in a right-hand 
 direction ; that is, in the same direction as the driving pinion B. 
 
 For reverse, band 7 is applied to the drum /, which has the 
 reversing pinion K keyed to it, being thus held stationary when 
 pinion B is rotated by the engine planetary pinion Z, is forced to 
 roll on K in a left-hand direction, carrying the pinion pin M and 
 pinion driver PI with it. 
 
 Direct drive is obtained by engaging the high-speed clutch 
 
106 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 N) which locks the reversing gear K to the driving shaft J., and 
 since two equal gear B and K are now secured to the shaft A^ the 
 planetary pinions are locked against axial motion and the whole 
 transmission revolves as a unit. 
 
 Sliding-gear Type. The sliding-gear type of transmission 
 consists of two parallel shafts mounted on suitable bearings in a 
 housing called the transmission case. The first of these shafts is 
 known as the primary or main driving shaft. This shaft is 
 divided into two parts, the forward or driving part and the rear 
 or driven part, the latter being provided with a bearing at its for- 
 ward end, inside the former. The second of these shafts is known 
 as the secondary or countershaft. The driven part of the main 
 shaft is either squared or provided with integral keys and carries 
 the sliding gears, whose common hubs have squared holes or key- 
 ways to coincide with the shaft to make a sliding fit upon it. The 
 driving part of the main shaft is provided with a gear, which 
 meshes with a gear on the countershaft and forms a drive for the 
 latter. The countershaft has a number of gears fixed upon it, 
 depending upon the number of speeds. The gears on both shafts 
 are so spaced that by shifting the primary set corresponding 
 gears on the two shafts can be brought into mesh successively 
 without interference from the other gears. Shifting of the slid- 
 ing set is accomplished by means of a hand lever located con- 
 veniently to the operator and a suitable connecting linkage. The 
 shifter rod carries a fork, which is attached to the gears in such 
 a manner as to permit them to rotate with their shaft. 
 
 There are two common arrangements of shafts. In some 
 cases the countershaft is located below the main shaft, while in 
 others the two shafts are located in a horizontal plane. 
 
 When the shafts are placed vertically the case is generally 
 cast in one piece, with a large hole cover plate for inspection pur- 
 poses. When the shafts are placed in a horizontal plane, the case 
 may either be cast in one piece or in halves joined through the 
 centers of the bearings. 
 
 There are three general methods of mounting the sliding gear 
 transmission: combining them with the motor to form a unit 
 power plant, individual mounting on a sub-frame or main frame 
 cross members, and combining them in a unit with the jack shaft. 
 
 All of these mountings may be made with a more or less de- 
 gree of flexibility. Three-point support is most generally re- 
 sorted to, with the intention of relieving the case of the stresses 
 set up by frame weaving. 
 
THE CLUTCH AND TRANSMISSION 
 
 107 
 
 Progressive Sliding Type. 
 In the progressive type 
 of transmission all sliding 
 gears are moved simulta- 
 neously when a speed 
 change is made. The sev- 
 eral speeds are arranged in 
 a fixed succession as the 
 combination of sliding 
 gears is progressively 
 shifted. It is thus neces- 
 sary to shift into the low- 
 speed gear first and progress 
 to the high. 
 
 Fig. 78 is a diagram- 
 matic view of a three-speed 
 and reverse progressive 
 transmission which is used 
 on a number of heavy com- 
 mercial cars. 
 
 High speed is obtained 
 by meshing the jaw clutches 
 formed integral with the 
 sliding member and the 
 constant mesh gear F. 
 Second speed is obtained 
 by moving the sliding mem- 
 ber backward and mesh- 
 ing gears D and E, so that 
 the drive is through gears 
 F, /, E and D. For low 
 speed the sliding member is 
 moved backward so that 
 the gear B will mesh with 
 the gear C on the counter- 
 shaft, and the drive is 
 through the gears F, /, C 
 and B. For reverse, gear 
 B of the sliding set is 
 meshed with the reverse 
 pinion #, which is con- 
 stantly in mesh with the 
 
 U 
 
 FIG. 78. Diagram of Three-Speed 
 and Eeverse Progressive Sliding-Gear 
 Transmission. 
 
108 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 gear H on the countershaft, .and the drive is through gear F, I, 
 H, G and B. This also illustrates a unit construction of jack 
 shaft and transmission. 
 
 Fig. 79 illustrates the 
 non-direct type of change 
 gear, the principle of op- 
 eration being similar to the 
 above, excepting that the 
 high speed is obtained by 
 meshing gears instead of 
 jaw clutches, while the up- 
 per shaft forms the drive 
 and carries the fixed gears. 
 The lower is the driving 
 shaft and carries the slid- 
 ing gears. Since the high 
 speed is obtained by mesh- 
 ing gears, the drive shaft 
 may be constructed in one 
 piece. 
 
 The principal objection 
 to the progressive type is 
 that it requires long shafts, 
 which are likely to be in- 
 efficiently rigid and to 
 spring and bend under the 
 thrust of the gear teeth, 
 causing noisy and inefficient 
 operation. The great length 
 of this transmission is 
 mainly due to the fact that 
 that the gears on each of 
 the shafts must be spaced 
 relatively far apart, so as to 
 avoid interference. 
 
 FIG. 79. Non-Direct Progressive Type. 
 
 Selective Sliding Type. 
 This objection is over- 
 come j n the selective gliding 
 
 type, as two sliding sets 
 
 are used. By comparing the two types it will be noted that the 
 latter is much more compact. It also has an advantage in that 
 
THE CLUTCH AND TRANSMISSION 
 
 109 
 
 the operator may change directly from one speed to any other 
 without passing through the intervening gears. 
 
 Fig. 80 shows a three-speed 
 forward and reverse selective 
 type transmission. The primary 
 shaft is squared and carries two 
 which 
 
 sliding 
 
 gears, 
 
 are op- 
 
 erated by independent shifter 
 rods. The countershaft is driven 
 through constant mesh gears A 
 and B, A being driven by the 
 drive shaft extending from the 
 clutch. In effecting the different 
 speeds, gear C is moved forward 
 and meshed with gear D for low 
 speed, while for reverse it is 
 moved backward and meshed 
 with the reverse pinion E, which 
 is in constant mesh with the re- 
 verse gear II on the counter- 
 shaft. For second speed the gear 
 F is meshed with gear (2, while 
 for high speed gear /, which is 
 integral with gear F, is moved 
 for\vard and meshed with the in- 
 ternal gear formed integral with 
 the constant mesh gear A. This 
 forms another type of jaw clutch, 
 and in some cases the jaw clutch 
 described above is used for effect- 
 ing the high speed. 
 
 A typical unit power-plant 
 transmission is shown in Fig. 81. 
 This transmission is intended for 
 low-powered delivery cars and 
 is provided with ball bearings 
 for the main shaft while the four 
 counter-shaft gears are cut in 
 one and are provided with plain bearings. This shows the 
 method of mounting the clutch on the forward main shaft. 
 
 Fig. 82 depicts a typical four-speed transmission for amidship 
 mounting. The main shaft is mounted on ball and roller bear- 
 
 FIG. 80. Three Speed and Re- 
 verse Selective Sliding Transmis- 
 sion. 
 
110 MOTOR TEUCK DESIGN AND CONSTRUCTION 
 
 CHANGE GEAR V a 
 
 CLUTCH/]\ BRAKE 
 PEDAL II PFDAL 
 
 FIG. 81. Conventional Type of Unit Power Plant Transmission and Con- 
 trol Mounting. 
 
 FIG. 82. Four Speed Selective Sliding Gear Transmission for Amidship 
 
 Mounting. 
 
THE CLUTCH AND TEANSMISSION 
 
 111 
 
 ings, while the countershaft is mounted on roller bearings. The 
 shifter rods are mounted in the cover and are provided with locks 
 for the various speeds. High speed is obtained by meshing two 
 jaw clutches this is the direct drive, third by meshing gears A 
 and B, second by gears G and D and low speed through gears E 
 and F. For reverse speed two idler gears G and H are used, 
 which are so arranged that they may be moved along their shaft 
 and meshed with gears E and F, the latter being held in its 
 neutral position. 
 
 FIG. 83. Constant Mesh Type of Selective-Sliding Gear Transmission. 
 
 The positive clutch type of transmission is somewhat related 
 to the selective sliding gear type. However, the gears remain 
 constantly in mesh, and the gears on the main shaft are normally 
 free to turn thereon, but may be fixed to the shaft by positive 
 clutches. These clutches, when of the jaw type, are similar to 
 those mentioned above, while internal and external gears may 
 also be used as positive clutches. The gears on the main shaft are 
 fixed while the clutches are free to slide upon keys or squared 
 portions of the shaft. 
 
 In this type the speed changes are obtained by the individual 
 clutches, but since the high speed is direct through the case and 
 the speed of the countershaft is reduced through the constant 
 mesh gears, a provision must be made so that the latter shaft 
 
112 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
THE CLUTCH AND TRANSMISSION 113 
 
 cannot turn on its bearings. This is accomplished by disengag- 
 ing a clutch on the countershaft, simultaneously with the engage- 
 ment of the high-speed clutch. Fig. 83 illustrates this type of 
 transmission. It also presents a method of driving all four 
 wheels by the addition of another shaft and silent chain. 
 
 An Automatic Engagement Type. Fig. 84 illustrates the type 
 of jaw-clutch transmission used on the Vulcan trucks. The 
 clutches are shifted automatically and are slightly undercut so 
 that they will not release until the driving pressure is removed, 
 while the change from one speed to another is made by means of 
 springs. This action is accomplished as follows: moving the 
 gear-shift lever compresses a set of springs which control the 
 arms which move the jaw clutches. However, as the clutches are 
 undercut this spring action has no effect, but just as soon as the 
 engine speed is momentarily reduced there is a tendency for the 
 vehicle to drive the engine, which instantly frees the jaw clutch, 
 which, under the action of the compressed springs already set by 
 the movement of the gear-shift lever, forces the clutch to take up 
 its new position, engaging the desired speed. This means that 
 slightly throttling the engine and releasing the clutch will 'always 
 effect the desired change of gears, but this may not take place 
 until any desired moment after the gear-shift lever -has been 
 moved. By this arrangement it is possible for the driver to ap- 
 proach a hill and before reaching it, if he thinks it too steep for 
 the highest speed, he can set the lever for the next speed. The, 
 jaw clutch will not shift as long as the engine is driving until at 
 the desired moment on the hill, by releasing the clutch the .change 
 will be automatically effected. 
 
 Transmission gears are usually lubricated by a non-fluid oil. 
 For easy introduction of the lubricant, a hole is provided in the 
 cover plate, which is enclosed by a screw plug, while a drain plug 
 is usually placed at the bottom so that the stale lubricant may be 
 washed out with kerosene or gasoline. The bearing caps are in- 
 variably provided with felt washers, while all other parts are pro- 
 vided with paper gaskets, to prevent the lubricant from working 
 out of the case. 
 
CHAPTER VIII 
 
 UNIVERSAL JOINT AND PROPELLER SHAFT 
 
 THERE is a difficulty in transmitting the power of the motor 
 to the transmission or rear axle which has to be met by a special 
 piece of mechanism. In the chain-driven vehicle the motor and 
 transmission usually remain in alignment when the vehicle is 
 standing still, however, road vibrations and the nature and loca- 
 tion of the load usually cause frame deflexions which tend to de- 
 stroy this alignment, while with a live rear axle the motor is pro- 
 tected from bouncing up and down by the chassis springs, and 
 the road wheels are continually bouncing over the rough surface 
 of the road. This means that at one moment the axle is in line 
 with the motor and the next moment it may be several inches 
 above or below the motor center. 
 
 A rigid shaft in the case of a chain-driven vehicle would bind 
 unless the alignment was perfect and provision made to prevent 
 frame deflexion, while with a live rear axle the shaft would bend 
 and bind in its bearings and the whole transmission system would 
 be put out of commission in a short time. To overcome this, the 
 shaft which is termed the drive or propeller shaft is made flexible 
 
 to a certain extent by 
 means of universal joints, 
 sometimes called Hooke 
 or Cardan joints. 
 
 These universal joints 
 serve the purpose of con- 
 necting shafts whose axles 
 lie in the same plane, but 
 make an angle with each 
 other and are particu- 
 larly required when the angle varies between the shafts in service. 
 There are various types and perhaps the simplest universal 
 joint consists of a squared block secured to one of the shafts to 
 be connected, fitting in a square hole in a sleeve secured to the 
 other shaft. The four faces of the block are curved in the direc- 
 tion of the axis of the shaft to which the block is fastened. This 
 type of joint is shown in Fig. 85. 
 
 114 
 
 FIG. 85. 
 
 One of the Simplest Universal 
 Joints. 
 
UNIVEESAL JOINT AND PKOPELLER SHAFT 115 
 
 Fig. 86 illustrates a somewhat different type. This consists 
 of six internal and external teeth; the external teeth are curved 
 in the direction of the 
 axis of the shaft and mesh 
 with teeth cut into the 
 housing. This joint is pro- 
 vided with a pressed steel 
 cover and packing wash- 
 ers to retain the lubricant. 
 The above types may be FlG> 86> Universal with Internal and 
 properly termed align- External Teeth, 
 
 ment joints, since they are 
 
 only used between the clutch and transmission, when only slight 
 angular movement exists, Fig. 86 being the type furnished with 
 
 all sizes of the well-known 
 Hell -Shaw universal clutch. 
 These joints also constitute 
 slip joints, since they permit 
 movement for clutch disen- 
 gagement. 
 
 The cross type of uni- 
 versal is depicted in Fig. 87 
 and consists of two forks, each 
 of which is secured to one of 
 the shafts to be connected to 
 each of the forks by a pin. 
 In this type of joint, the 
 axes of the two pins do not intersect, but are at some distance 
 from each other. However, there is an advantage in having the 
 pins both in the same 
 plane. This end can be at- 
 tained in various ways by 
 either using pins of dif- 
 ferent diameters and pass- 
 ing one through the other, 
 by one long and two short 
 pins, by forging the pins FlG . 88 . Split-ring Type Universal, 
 integral with a common 
 center or forming them integral with the forks. 
 
 In the joint shown in Fig. 88 the cross is replaced by a split 
 ring, which carries the pin bearings, while the pins are forged 
 
 FIG. 87. 
 
 Cross Type Universal with 
 Forks. 
 
116 MOTOR TEUCK DESIGN AND CONSTRUCTION 
 
 integral with the forks. The ring is divided to facilitate assem- 
 bling and thus permits the pins to have their axes in the same 
 plane. This type of joint could also be made by forming the pins 
 integral with a central ring and providing forks with separate 
 bearing caps. 
 
 Fig. 89 illustrates the Swenson joint, which in some respects 
 is similar to the split-ring type. It consists of a fork with in- 
 tegral pins and a large pin passing through a hub and supported 
 
 FIG. 89. Swenson Universal Joint. 
 
 by square bushings in a ring. The integral pins are also provided 
 with square bushings which fit into slots in the ring. The bush- 
 ings are held in position by two discs which together with the 
 ring form a housing. 
 
 All universal joints are of the pin type with the exception of 
 the leather or fabric-disc type, however, there are various meth- 
 ods used to provide angular movement. The Hartford joint, 
 
 FIG. 90. Hartford Block and Trunnion Type Joint. 
 
 shown in Fig. 90, is termed a slotted shell and trunnion type. 
 This consists of a cup -shaped steel forging secured to one of the 
 shafts with two diametrically opposite longitudinal slots milled 
 into the shell. The other shaft is provided with a ball-shaped 
 end, fitting the interior of the shell and provided with a pin ex- 
 tending into the slots. Hardened steel trunnion blocks are inter- 
 posed between the pins and the walls of the slots, to distribute 
 the bearing pressure. This type also serves as, a slip joint and is 
 easily enclosed with a tubular steel casing and a leather boot. 
 
UNIVEKSAL JOINT AND PROPELLER SHAFT 117 
 
 Since this type of joint permits endwise movements of the shaft, 
 some provision must be made to hold the latter in proper relation 
 to the two joints. Coil springs are used for this purpose. 
 
 FIG. 91. Evans Type of Block and Trunnion Universal Joint. 
 
 The Evans joint (Fig. 91) is also of the trunnion type with 
 trunnion blocks located in diametrically opposite slots; however, 
 the outer walls of these slots are curved in the direction of the 
 axis of the shaft, thus distributing the pressure to the three walls 
 
 FIG. 92. Detroit Ball Bearing Universal Joint. 
 
 of the slots. The pins which carry the trunnion blocks are forged 
 integral with the slip yoke. The joint is enclosed by a pressed 
 steel housing provided with a packing washer and spring to re- 
 tain lubricant. 
 
 FIG. 93. The Hoosier Universal Joint. 
 
 In the Detroit universal joint shown in Fig. 92 the trunnion 
 blocks are replaced by steel balls which operated in a pressed 
 steel housing provided with diametrically opposite slots. The 
 construction is similar to fig. 89. 
 
118 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 The joint shown in Fig. 93 is sim- 
 ilar to the block and trunnion type, 
 however, the yoke is provided with 
 diametrically opposite slots and the pin 
 is provided with square ends which fit 
 into the slot. This pin is inserted 
 through a bushing in the hub of the 
 joint which is spherical while the hous- 
 ing and yoke are also provided with 
 spherical surfaces. 
 
 Perhaps the most popular types of 
 joints in use at present are the Spicer, 
 Arvac, Hartford and Blood shown in 
 Figs. 94 to 97. The Spicer joint is some- 
 what related to the ring type. It com- 
 prises a central ring with pins forged 
 integral, having their axis in the same 
 plane. One forked end is forged in- 
 tegral with a hub which bolts to the hub 
 of the permanent shaft end, while the 
 other fork may have either a short hub 
 for permanent attachment to the pro- 
 peller shaft or a long hub to provide a 
 slip joint. The bearing ends of the fork 
 have an opening large enough to permit 
 inserting the pins, while they are also 
 bored out large enough to take hard- 
 ened and ground bushings, which hold 
 the ring and its pins in position. These 
 bushings and fork ends have circular 
 grooves cut in them so that a soft wire 
 can be inserted to hold the bushings in 
 place. The mechanism is enclosed in a 
 pressed steel housing which also serves as 
 a retainer for the lubricant. 
 
 The Arvac joint (Fig. 95) differs 
 from those depicted above, as it con- 
 sists of a ball yoke and socket fitted 
 with a cross block and pins enclosed in 
 a forged steel housing. This housing 
 supports two bushings which provide 
 the bearings for the king pin, thus pro- 
 
UNIVERSAL JOINT AND PKOPELLER SHAFT 119 
 
 viding a light but strong driving member of tubular section. 
 The bushings which fit into the yoke are provided with shoulders 
 and form the bearings for the yoke pin. Bushings are provided 
 with oil grooves and the oblong space provided by the housing 
 forms grease pockets, this grease being oscillated by centrifugal 
 action and this action forces the lubricant into the oil grooves of 
 
 FIG. 95. Arvac Universal Joint and Propeller Shaft Assembly. 
 
 the bushings. The pins are a press fit into the cross, practically 
 forming a one-piece driving member. The yoke end is provided 
 with a spherical surface which with a packing contained in a re- 
 tainer forms a seal to hold the lubricant. 
 
 The Hartford pin joint (Fig. 96) is of the type using one 
 long and two short pins, and is related to the ring type in that a 
 central ring is used which carries the bushings that form the 
 bearings for the pins. One fork end in forged integral with a 
 hub which bolts to the hub of the permanent shaft end. This 
 hub has lugs in the form of a clevis so that the load is placed on 
 
 FIG. 96. Hartford Pin Type Universal Joint. 
 
 both ends of the pin instead of at one point. The long pin passes 
 through both extensions of the yoke end and all pins are held in 
 place by washers and cotter pins. The mechanism is enclosed in 
 a pressed steel housing provided with packing to retain lubricant. 
 The Blood universal joint is depicted in Fig. 97. This is also 
 of the pin type, however, it is of the open construction since no 
 housing is provided. It consists of a central member in the form 
 
120 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 \/ 
 
 _K 
 
 v/ 
 
 \7 
 
 of a cube, which is provided with a large 
 and small pin, the latter pin passes 
 through this cube and large pin and is 
 locked in position by a locking pin. The 
 two forks are provided with bushings and 
 the outer ends of these are enclosed by 
 caps which contain the lubricant. 
 
 The universal joint assembly shown 
 in Fig. 98 represents ~the type used on 
 the military class A and B trucks. It is 
 essentially a pin joint and follows ac- 
 cepted practice, being provided with a 
 central cross into which the pins are 
 pressed. In order to form a solid unit 
 these parts are locked by a bolt which 
 passes through them. These pins pivot 
 in hardened and ground-steel bushings 
 which are pressed into the fork and 
 flange yoke. The entire assembly is en- 
 closed in a pressed steel housing. A 
 leather boot is attached to the propeller 
 shaft and this with the housing forms the 
 grease retainer. 
 
 These universals are suitable for 
 use between the clutch and transmission 
 and the latter and the rear axle. In com- 
 mercial vehicles two universals are nec- 
 essary for either location when amid- 
 ship mounting is provided for the trans- 
 mission. In the rear position one must 
 always be provided with a slip joint or 
 fitting, while when a slip joint is used 
 at the front end it compensates for 
 variations in shaft and frame lengths, 
 clutch movement and is also an advan- 
 tage in assembling. The slip joint in 
 the rear must be provided to compen- 
 sate for variations in the distance be- 
 tween the axle and the transmission due 
 to thfe play of the springs. This joint 
 may either be' a square or fluted shaft 
 with a corresponding hub or sleeve. 
 
UNIVERSAL JOINT AND PROPELLER SHAFT 121 
 
 FIG. 98. Universal Joint Used on the Class B Military Trucks. 
 
 Fabric Joints. Leather and fabric universal joints have been 
 used for some time because they present several features not ob- 
 tainable with the mechanical type. The principle advantages 
 are silent operation without wearing surfaces requiring no lubri- 
 cation. Since there is no friction they are considered highly 
 efficient in the transmission of power. However, this joint is not 
 adapted to conditions when there is a great angularity between 
 shafts since the flexibility of the disc is depended upon to com- 
 pensate for this angular movement and also the elongation in the 
 shaft. Experience generally with this type of joint has not been 
 uniformly successful and extreme care is necessary in their de- 
 sign. Owing to its limitations in angular movement it is mostly 
 used between the clutch and transmission when the angular move- 
 ment is relatively small. 
 
 A typical joint of this type for use between clutch and trans- 
 mission is shown in Fig. 99. It consists of several similar spiders 
 usually three armed, fastened to the ends of the shafts to be con- 
 
 FIG. 99. Thermoid Fabric-Disc Type of Universal. 
 
 nected and of a number of leather or fabric discs bolted between 
 the spiders. The arms of the two spiders are staggered so that 
 any arm of one of the spiders is located midway between two 
 arms of the other spider. Three, four or five discs may be used 
 and individual discs ar6 often spaced by steel washers. 
 
122 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 Fabric discs are usually rubberized. These are built up of 
 layers of fabric with the warp of succeeding layers at slightly 
 different angles. In fact the whole circle is divided into a num- 
 ber of parts equal to the number of layers in the discs and the 
 angle thus arrived at is the angle between the warp of adjacent 
 discs. 
 
 Propeller Shafts. Propeller shafts were originally made of 
 solid section, however, with the sudden increase in shaft-drive 
 construction, especially where the transmission was in a unit with 
 the motor, came a decided tendency to use either two shafts and 
 three universal joints, or a large tubular shaft and two universal 
 joints. The advantage of the tubular lies in its reduced weight 
 
 and consequently the reduced 
 whipping effect and pressure 
 on the bearings. A large tubu- 
 lar shaft is shown in Fig. 94 
 and a divided shaft of solid 
 section in Fig. 97. 
 
 These tubular shafts are 
 made of 40 carbon seamless 
 tubing and are attached to stub 
 .-.... .... , shaft which form the connec- 
 
 gr * i NXV 
 
 T : " 7~i tions with the universal joints. 
 
 lj The ends of these shafts are 
 
 ^- J I m JK ->' ^ jjs* tJfe^^ generally made a shrink fit 
 
 into the tube and then welded. 
 The manufacturer of the Ar- 
 vac universal joint uses the 
 shrink joint fit for shafts, but 
 these have keyways cut into 
 them so that the tube while 
 being shrunk over the shaft 
 can also be swaged into the 
 keyways, thus strengthening 
 the welded joints in the pro- 
 peller shaft and permitting 
 the driving strains to be taken 
 by the swaged portion of the tube. 
 
 Propeller Shaft Mountings. When two shafts are used a uni- 
 versal is generally attached to the transmission, while the other 
 end of the shaft is mounted in an anti-friction bearing such as a 
 
 FIG. 100. Lippard Stewart Propeller 
 Shaft Mounting. 
 
UNIVERSAL JOINT AND PKOPELLER SHAFT 123 
 
 ball or roller bearing. While this divided propeller shaft is not 
 new, the use of a tubular shaft no doubt has an influence on the 
 problem, and this center bearing is receiving considerable thought 
 at present, which is evident through the number of designs in use 
 at present. 
 
 The construction shown in Fig. 100 consists of a self-align- 
 ing ball bearing mounted in a housing which is bolted to a cross 
 member of the frame. A shoulder on the shaft and the hub of 
 the universal joint hold the bearing in position while its self- 
 aligning feature and the end play allowed in the housing pro- 
 vides for frame deflexions and variations in shaft length. 
 
 FIG. 101. Globe Propeller Shaft Mounting. 
 
 On the Globe trucks a heavy duty Hyatt bearing is mounted 
 on a stub shaft welded to the forward propeller shaft. This 
 bearing is mounted in a bracket which is in the form of a hinge. 
 This type of mounting may be so placed as to provide a straight- 
 line drive from the transmission to the rear axle, since any de- 
 flexion on the side rails of the frame may be neglected, due to the 
 hinged bracket providing the self-aligning feature. The slip 
 joint is mounted as close to the bearing as possible, as shown in 
 Fig. 101. 
 
 On several models of Diamond T-trucks four universals and 
 three shafts are used, the center being supported by two roller 
 bearings as illustrated in Fig. 102. Two slip joints are used, one 
 immediately back of the transmission and the other back of the 
 center shaft mounting. The bearings are Timken rollers and 
 mounted in a dust-proof housing and provided with adjustment. 
 
124 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 FIG. 102. Diamond T Center Bearing Mounting for Divided Propeller 
 
 Shaft. 
 
 On the Bethlehem trucks the Barker floating bearing is used 
 which permits the use of but two universal joints and a long 
 shaft. .This is depicted in Fig. 103 and is so mounted on the pro- 
 peller shaft as to permit it to float between coil springs. This 
 bearing has a free movement up and down with the propeller 
 
 shaft in one of the slots of a pivoted 
 arm. A coil spring on the shank of 
 the bearing, which passes through the 
 slot in the arm, slightly resists free 
 movement of the shaft away from the 
 arm, and another coil spring at the top 
 of the arm acts similar in the opposite 
 direction, the arm being pivoted at the 
 lower end. This pivot arm is sup- 
 ported by a bracket attached to a cross 
 member of the frame. 
 
 To secure the highest efficiency and 
 absence from vibration, care should be 
 observed to have the pins at opposite 
 ends of the assembly parallel, as this 
 will eliminate vibration which may be- 
 come serious if the shaft whips as the 
 velocity of the front joint must be equalized by the rear joint, since 
 the velocity varies during each quarter revolution. As the bear- 
 ing pressures are necessarily high, proper means for lubrication 
 must be provided. The 'assembly proper is usually provided with 
 a housing to retain lubricant and means for inserting same. 
 
 FIG. 103. Barker Propel- 
 ler Shaft used en the Beth- 
 lehem Trucks. 
 
CHAPTER IX 
 
 THE DIFFERENTIAL 
 
 ANOTHER unit of the power transmission system which must 
 be used is the differential. It is a well-known fact that in turn- 
 ing a curve the outer wheels travel faster than the inner ones. 
 To compensate for this a differential is used, sometimes called a 
 compensating or equalizing gear. 
 
 If the driving wheels were solidly connected to each other by 
 the axle and that axle driven by a chain or shaft from the center 
 or thereabouts, great stress would be placed upon the transmis- 
 sion tires and other parts, owing to the fact that both wheels in 
 turning a corner would travel at the same speed, but owing to the 
 fact that the outside one must travel faster than the inner one, 
 the latter would be forced around or skidded on the road. 
 
 The layman often experiences difficulty in understanding the 
 differential, as it is always enclosed in a casing and is entirely out 
 of sight and unless he has a chance to see it in the repair shop or 
 factory, he has little chance to familiarize himself with its action 
 by actual observation. 
 
 The power of the motor is applied either to a centrally divided 
 rear axle (usually termed a live axle) or to a jack shaft, thence 
 by chains and sprockets to the rear wheels, turning loose on a 
 dead rear axle. The first condition applies to all shaft-driven 
 vehicles, such as the level gear, internal gear, double reduction 
 and worm drive, the second applies to chain-driven vehicles. The 
 action of the differential is identical for either of the above-men- 
 tioned drives. It is mounted in the rear axle housing for all 
 shaft-driven types, while for the chain-driven types it is mounted 
 in the jack shaft housing. 
 
 The object of the differential is to permit of equally dividing 
 the driving effort of a single source of motive power between the 
 two driving wheels and to allow cars driven through wheels on 
 opposite sides to be freely steered. In turning a corner, the driv- 
 ing effort must be divided in such a way that one- wheel may 
 rotate faster than the other and still receive the same driving 
 force as the other. In other words, the driving force must be 
 equally divided between the driving wheels under all conditions 
 for both forward and backward motion. 
 
 125 
 
126 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 The division of the driving effort is very desirable, except 
 when the driving wheels are on ground with greatly different co- 
 efficient of adhesion. For instance, if one wheel got into a mud 
 hole, it might not have sufficient adhesion to prevent it from spin- 
 ning under the turning effort impressed by the differential gear 
 and it would then be impossible to propel the car except by lock- 
 ing the differential, because the turning effort of the wheel stand- 
 ing on solid ground would be no greater than the turning effort 
 corresponding to the coefficient of adhesion of the wheel in the 
 mud hole. For this reason differential locks are often provided. 
 
 FIG. 104. Bevel-Gear Type Differential. 
 
 This lock may be left engaged as long as all four wheels move 
 in a perfectly straight path. When, however, a vehicle is to be 
 moved in a curved path as in turning a corner the driving wheels 
 must revolve at different speeds, since the outer one has to cover 
 a longer distance in the same time than does the inner wheel 
 which is on the inside of the curve. 
 
 There are three types of gear differentials in common use, viz., 
 the bevel type, the spur type and the helical type. 
 
 The bevel pinion type of differential, which is probably the 
 most common form is illustrated in Fig. 104. It consists of the 
 following parts: a housing A, which is usually made in halves, 
 two bevel gears B and C secured to the differential or driving 
 shafts D and E respectively; a two, three or four-armed spider 
 F, on the radial arms of which are carried bevel pinions G, G-l, 
 G-%, G-3 meshing with both of the bevel gears B and G. To the 
 housing A of the differential is usually bolted a bevel gear H for 
 driving it, but this gear forms no part of the differential proper. 
 It will be understood that the differential shafts D and E, either 
 
THE DIFFERENTIAL 
 
 127 
 
 have secured to their outer ends road wheels or sprockets, which 
 drive the road wheels through chains. Gear H meshes with the 
 bevel driving pinion. 
 
 The action of the differential may be explained as follows: 
 The spider F is held to the housing A and the turning effort or 
 torque which is applie'd to the housing by means of the driving 
 or ring gear //, and its pinion is equally divided by the bevel 
 pinion G between the gears B and C. As long, therefore, as the 
 resistance to motion of the two bevel gears B and G (in other 
 words to the motion of the driving road wheels of the car), is the 
 same, the two wheels will turn at the same speed. If, however, 
 the steering wheel is turned so as to move the car to one side or 
 the other, the driving wheel on the side to which the car turns is 
 automatically held back with a force equal to the road adherence. 
 The differential gear, B or C as the case may be, on that side will 
 
 FIG. 105. Spur-Gear Type Differential. 
 
 then turn slower and its mate on the other side will turn corre- 
 spondingly faster, while the bevel pinion G between them will 
 turn on their journals at a speed corresponding to the difference 
 in speed of rotation of the two bevel gears B and C. While a 
 vehicle is turning a curve, although the speeds of the two driv- 
 ing wheels are unequal, the tangential forces acting at their cir- 
 cumference are equal. 
 
 Another form of differential which has been extensively used 
 is known as the spur type illustrated in Fig. 105. The action of 
 this can be best explained by comparison with the bevel type. 
 The bevel gears B and C are here replaced by spur gears A and 
 
128 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 B fastened to the differential shafts G and D respectively. While 
 the inner sides of the hubs of these spur gears come close to- 
 gether, the inner edges of the gears themselves are at some dis- 
 tance apart. Meshing with these two spur gears A and B are 
 two, three or four sets of spur pinions, E, F. These spur pinions 
 have a width of face almost twice that of the spur gears A and B. 
 The outer portion of the face of each pinion meshes with one of 
 the spur gears, and the inner portions of the faces of the pinions 
 mesh together. It will be readily understood that if the casing 
 of the differential G is held stationary and the spur gear is re- 
 volved by hand or otherwise in a clockwise direction, the pinion 
 E meshing with it is revolved in a counter-clockwise direction : the 
 pinion F meshing with E is revolved in a clockwise direction and 
 the gear B is revolved in a counter-clockwise direction. That is, 
 gear B is rotated in an opposite direction to gear A, exactly as 
 
 with the bevel gear dif- 
 erential. In regular op- 
 eration the turning effort 
 is, of course, transmitted 
 to the differential housing 
 by means of gears and 
 the turning effort thus re- 
 ceived by the housing is 
 equally divided by the 
 sets of spur pinions be- 
 tween the spur gear A and 
 B, that is, between the two 
 driving road wheels. The 
 properties of the spur- 
 gear differentials are ex- 
 actly the same as those of 
 the bevel-gear differential. 
 
 The problem of working out a neat and all around satis- 
 factory differential lock for either of the above types presents 
 considerable difficulty, which is probably the reason that this 
 device is not more extensively used. Fig. 106, this lock which 
 is in the form of a four- jaw clutch, one member being keyed to 
 the drive shaft and free to slide upon it, while the other is keyed 
 to the differential case. Meshing the two clutch members locks 
 the differential, since one shaft is locked against the other through 
 the differential housing. 
 
 FIG. 106. 
 
 A Neat and Simple Differen- 
 tial Lock. 
 
THE DIFFERENTIAL 129 
 
 A differential lock can also be provided with the spur type 
 and an excellent example is illustrated in connection with Fig. 
 105. A large flange is so mounted on the differential housing 
 that it can be moved endwise, and the stud of one of the spur 
 pinions extends beyond the housing. Half of the end of this stud 
 is milled off so that the sliding member can be moved in, thus 
 preventing the pinion from turning, which locks the entire dif- 
 ferential. 
 
 The ordinary type of differential mentioned above presents 
 certain disadvantages, the principal objection being that it pro- 
 motes skidding. Recently several designs of differentials have 
 been developed in which this common objectionable feature has 
 been eliminated. This type is known as the helical gear type. 
 
 In the Powrlok device, there are two or more pinions mounted 
 in the differential housing which is rotated by the engine, and 
 also two crown wheels are attached to either driving wheel. But, 
 in addition, there are worm gears interposed between the pinions 
 and the crown wheels, the teeth on which are shaped to corre- 
 spond. These worms are 
 mounted in the differential 
 casing as shown in Fig. 107 
 with their axis at right angles 
 to those of the pinions. It 
 will be seen, then, that the ro- 
 tation of the differential hous- 
 ing in the usual way causes 
 FIG. 107. Powrlok Differential. both pinions and worm gears 
 
 to be carried around bodily 
 
 in rigid relation to each other, whilst at the same time both pin- 
 ions and worms have a power of rotation upon their own axis, so 
 that they can be moved rotationally, but not bodily, in relation 
 to each other. 
 
 When road resistance is sufficient to give adhesion to each 
 driving wheel, both wheels are equally driven, the crown wheels 
 to which they are attached being carried bodily round by the 
 worms in which they are in engagement, just as, with an ordinary 
 differential, they are carried round by the pinions. But when 
 road resistance upon one wheel is reduced to a point at which it 
 loses adhesion, and would, with the ordinary differential, start 
 spinning, nothing of this kind .happens, because the angle of the 
 worms is such that whilst the crown wheels can drive the worms, 
 10 
 
130 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 the worms cannot drive the crown wheels, and, as a consequence, 
 the differential is locked so far as any movement of the wheel in 
 relation to the differential is concerned. The axle becomes for all 
 practical purposes a solid one, and all the drive is taken by the 
 wheel, which is for the moment supported on firm ground and 
 can take advantage of its grip. 
 
 When both wheels are on firm ground and the vehicle is trav- 
 eling freely, the differential is enabled to act in the usual manner 
 when turning corners, by reason of the fact, already alluded to, 
 that the crown wheels can drive the worms. Each driving wheel 
 is attached to its respective crown wheel, and when a curve in the 
 road is followed, the outer wheel is forced by its contact with the 
 
 m 
 is 
 
 FIG. 108. Exterior of the Walter Differential. 
 
 road to travel a greater distance than the inner one. The outer 
 wheel, therefore, revolving faster than the axle, turns the worm 
 in connection with it and so enables the central pinions to act and 
 react on the worms with a differential action and to distribute the 
 power to each wheel in the usual manner. 
 
 The Walter differential (Fig. 108) is also of the irreversible 
 worm-gear type, which drives both wheels regardless of the trac- 
 tion conditions of the other wheel and which still has a compen- 
 sating differential action. It consists of two pairs of spiral gears 
 mounted in a two-part housing, and meshing together and sep- 
 arately with worms in the housing and on the drive shafts. Both 
 halves of the housing are alike except for the bevel or ring-gear 
 flange. The two bolts which bolt the housing together set one- 
 half ahead of the other so that the spiral-gear pairs mesh directly 
 together. 
 
THE DIFFERENTIAL' 131 
 
 The operation of this device is as follows: The driving re- 
 sistance of the road wheels tends to rotate the spiral gears on 
 their pins, but in opposite directions, but if one road wheel has a 
 greater resistance the inequality of force cannot drive the other 
 wheel faster as the spiral gear cannot drive the worm, so both 
 wheels are positively driven. When turning the outer wheel 
 rolls faster and so permits the inside wheel to turn correspond- 
 ingly slower, giving a compensating differential action. 
 
 Lately there has been a tendency to substitute an equalizing 
 gear for the differential which to certain extent eliminates its 
 disadvantages, since this equalizing device can be so arranged as 
 to limit the pull on one wheel to the amount required to slip the 
 other. However, as the use of these has been limited to low- 
 powered passenger cars they will not be considered in this chapter. 
 
 When all four wheels of a vehicle are used as driving wheels, 
 it is generally necessary to provide three differentials ; one in the 
 transmission case to equally divide the turning effort between 
 each pair of driving wheels and one for each front and rear drive. 
 
 Thus the differential is absolutely necessary in any form of 
 final drive used on commercial vehicles and it presents consid- 
 erable advantages in protecting all parts of the mechanism against 
 stress when turning corners. While it also has the disadvantage 
 of stalling a vehicle when one wheel gets into a mud hole. 
 
 This disadvantage may be overcome by providing a differ- 
 ential lock, this again places the responsibility upon the operator 
 and should he attempt to round a curve with the differential 
 locked, the tires and driving mechanism would be subjected to 
 considerable wear. Should this be done quite frequently, the 
 results would soon be noticeable. 
 
 In order to overcome the latter feature, this lock is operated 
 by a foot pedal and so arranged that it must always be held in 
 engagement. Removing the foot pressure disengages the lock, 
 thus providing for the poor memory of the operator. 
 
CHAPTER X 
 
 THE FINAL DRIVE 
 
 Chain, Bevel, Double Reduction, Internal Gear and Worm 
 Drive. From the transmission the power must be transmitted to 
 another unit from which it is converted into useful work at the 
 road wheels. In commercial car construction this is generally 
 termed the final drive. There are a variety of methods of trans- 
 mitting the power and in taking up the discussion of the final 
 drive, the writer will attempt to cover this subject as clearly as 
 possible and is offering illustrations of a number of different 
 types in use at present. The general problem of the final drive 
 resolves itself into the transmission of motion from one or more 
 revolving shafts to driving wheels flexibly connected to the frame 
 through axle and springs, and at the same time effecting a reduc- 
 tion in rotative speed between the driving shaft and rear wheels. 
 
 Chain Drive. During the past years the majority of commer- 
 cial cars were equipped with what is known as the double side- 
 chain drive. The principal objection to it is the attention re- 
 quired to obtain maximum efficiency. It is generally exposed and 
 dirt soon finds its way into the numerous bearings, causing rapid 
 wear. For a time, chain cases seemed to be the solution of the 
 problem, but they are not satisfactory and most makers started 
 experimenting with different types of shaft drives. This has 
 resulted in the introduction of the bevel gear, double reduction, 
 internal gear and worm gear rear axles. 
 
 In chain drive the power must be transmitted to a unit carry- 
 ing the driving sprockets, the differential and in some cases a set 
 of brakes. This unit is generally termed the jack shaft and may 
 be built integral with the transmission or in a separate unit, 
 mounted separately or bolted to the transmission. This jack 
 shaft is similar to and performs the same functions the bevel gear 
 rear axle in pleasure cars, excepting, of course, that it does not 
 carry the weight of the vehicle. For this purpose a dead rear 
 axle is used, which has spindles upon which the wheels and their 
 bearings are mounted. Various types of rear axles may be found 
 in use at present, their section being either round, square, rectan- 
 gular or I-beam. The jack shaft is usually equipped with one set 
 
 132 
 
THE FINAL DRIVE 
 
 133 
 
 of brakes, while the other set is mounted in the rear wheels. 
 However, some makers mount both sets of brakes on the rear 
 wheels. 
 
 Some method must be provided to take up the driving thrust 
 from the rear axle to the frame. For this purpose a radius rod 
 is provided, which also takes up the brake pull, and the reaction 
 due to chain pull, as well as allowing for adjusting the slack in 
 the chain. These rods are generally of the full universal type, 
 being pivoted on the jack shaft and the brake support or spindle 
 of the rear axle. They are sometimes provided with large coil 
 springs to take up abnormal shocks, when engaging the clutch or 
 backing up to a curb. 
 
 The chain drive in reality is a double reduction through two 
 units, one reduction being obtained through the bevel gears in 
 the jack shaft, while the other is obtained through the jack shaft 
 and rear wheel sprockets. 
 
 fiAV/US 
 
 ftOO 
 CONNECTION 
 
 FIG. 109. Sheldon Jack Shaft. 
 
 Fig. 109 illustrates the jack shaft built by the Sheldon Axle 
 and Spring Company, which was used on a number of commer- 
 cial cars, being a separate unit so arranged that a standard trans- 
 mission may be bolted to it. The differential is of the bevel-gear 
 type, while the working parts are mounted on ball bearings. 
 
 Fig. 110 depicts the Velie jack shaft which is a separate unit, 
 the transmission being mounted on a sub-frame, while the jack 
 shaft is mounted on the main frame. Like the Sheldon construc- 
 tion, the driving unit is so arranged that it may be removed 
 through the inspection cover opening without removing the jack 
 shaft unit from the chassis. The differential lock is also shown, 
 mounted on the right side of the differential housing. The jack 
 shaft is flexibly mounted on the frame, while a torque arm is used 
 to hold it in alignment. The differential and drive shafts are 
 mounted on roller bearings. Internal expanding brakes are pro- 
 
134 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
THE FINAL DRIVE 
 
 135 
 
 vided. The outboard bearing for the sprocket is mounted as 
 close as possible to the chain center, so as to overcome the high 
 tension in the chain on low 
 gear. 
 
 In Fig. Ill is shown 
 the Velie rear axle which 
 is of round section, hav- 
 ing a spring seat, which 
 also carries the brake 
 spider keyed to it by a 
 large bolt. The spring is 
 mounted above the axle 
 and retained by spring 
 clips. The radius rod is 
 mounted inside of the 
 spring and pivots on the 
 rear axle spindle. Inter- 
 nal expanding brakes are 
 mounted inside the brake 
 drum, to which the driv- 
 ing sprockets are attached. 
 This drum is attached to 
 the spokes of the wood 
 wheel by spoke clips, while 
 
 the w T heels are equipped with dual tires. Wheels have roller 
 bearings. 
 
 Fig. 112 illustrates the radius rod used on the Atterbury chain- 
 driven models. This rod is of the universal type, being pivoted 
 and hinged to jack shaft at the forward end and hinged to the 
 
 FIG. 111. Velie Eear Axle. 
 
 BRAKE SUPPQ&T 
 RADIUS ROD 
 
 FIG. 112. Atterbury Eadius Eod. 
 
136 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 brake support at the rear end, which in turn is found to pivot on 
 the rear axle spindle. An adjustment is provided at the forward 
 end on which is mounted a heavy coil spring. The rod is con- 
 structed in two sections, so 
 that the rear end may slide 
 upon the forward end, the 
 spring holding both ends 
 in their positions. When 
 the clutch is suddenly en- 
 gaged or when backing up 
 to a curb, this spring takes 
 up the abnormal shock by 
 compressing and permit- 
 FIG. 113. Peerless Jack Shaft Intregal ting the rear section to slide 
 with Transmission. over the forward one. As 
 
 soon as the force is re- 
 moved the spring expands and returns the rear end to its proper 
 position. This type of radius rod is also used on the Velie and 
 Lewis commercial cars. 
 
 Oil the Peerless truck, the jack shaft is built integral with the 
 transmission as shown in Fig. 113. It is similar to the construc- 
 tion described above, excepting that one set of brakes is mounted 
 on the jack shaft inside of the frame and anchored to the frame 
 cross-member instead of to the housing proper. The shafts are 
 not enclosed, but are mounted in anti-friction bearings attached 
 to the frame. With this construction the brakes are better pro- 
 tected from mud and water. Construction of this type may also 
 be found on several other cars. 
 
 The Vulcan radius rod and rear axle construction differ some- 
 what from the above in that the radius rod adjustment is placed 
 at the rear instead of the customary place near the jack shaft 
 sprocket. By referring to Fig. 114, it will be noted that the 
 radius rod proper is similar to a marine engine connecting rod 
 with caps bolted to the jack-shaft end which fit over a spherical 
 bearing. The rear end has three bosses, through which are in- 
 serted two guide pins and an adjusting screw. These guide pins 
 are retained by clamping bolts, while the adjusting screw is at- 
 tached to a yoke, through the outer ends of which the guide pins 
 pass. A large bolt passes through the heads of these and through 
 a bracket which pivots on the axle spindle, formed integral with 
 the brake support. The hub and brake drum are cast integral 
 
THE FINAL DRI\TE 
 
 137 
 
 and attached to the wheel by bolts and the wheels are mounted on 
 roller bearings. 
 
 FIG. 114. Vulcan Eadius Eod with Adjustment at Eear End. 
 
 The Kelly jack shaft (Fig. 115) illustrates a pressed steel 
 housing and a full floating construction which is quite accessible. 
 The housing proper is pressed in two halves and welded together, 
 while reinforcing tubes and flanges are used to strengthen it. To 
 this pressed steel jack-shaft housing is bolted a cast steel differ- 
 ential carrier or housing which carries the entire differential as- 
 sembly and also the transmission. Provision is made for inspec- 
 tion of the differential assembly by removing the pressed steel 
 cover from the rear of the jack-shaft housing. Each end carries 
 a supporting roller bearing mounted in sleeves and held in place 
 by the carrier and caps. An adjusting nut screws over each 
 sleeve, where it is easily accessible and is locked by a small key 
 on the carrier cap. 
 
138 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 The outer end of the jack-shaft housing terminates in ball 
 sleeves, which are riveted to it. These sleeves provide universal 
 movement for the entire unit when mounted in the chassis frame 
 and also a universal movement for the forward end of the radius 
 
 CARRIER 
 L HOU5IN6 
 
 HOUSING REINFORCING FLAME 
 AND TUBE 
 
 FIG. 115. Kelley-Springfield Floating Jackshaft with Pressed Steel 
 
 Housing. 
 
 rod. The ball sleeves accommodate a roller bearing held in posi- 
 tion against the shoulder of the drive shaft by a large lock nut 
 properly secured by lock wires. A large adjusting nut, contain- 
 ing a felt washer screwed into the end of the ball sleeve, bears 
 against the outer race of the bearing. Sprockets are bolted to the 
 flanges forged integral with the drive shafts and the bolts are 
 equipped with hardened steel bushings. They afford equal dis- 
 tribution of the shearing strains on the bolts, due to the drive of 
 the truck. 
 
 FIG. 116. Kelley Radius Eod, Brake and Rear Axle Construction. 
 
THE FINAL DRIVE 
 
 139 
 
 Fig. 116 illustrates the radius rod and double rear wheel 
 
 & 
 
 brakes of the Kelly trucks. The radius rod proper is a drop 
 forging and pivots from the brake spider. The chain adjustment 
 is incorporated at the front end by adjusting screws. The rear 
 axle is of I-beam section with integral spring pads. 
 
 FIG. 117. G.M.C. Eadius Rod and Eear Construction. 
 
 The G.M.C. one-, one-and-a-quarter and two-ton models have 
 similar constructions excepting for size, which varies on the dif- 
 ferent capacities. This is illustrated in Fig. 117, showing the 
 two-ton construction. The rear axle is of rectangular section 
 and has a long spindle upon which the spring seats, brake spider 
 to which the radius rod body is riveted and the wheels are 
 mounted. The hub and brake drum for the internal brake are 
 formed integral, while a separate brake drum is attached to the 
 wheel spokes for the external brake, both sets of brakes being 
 mounted in wheels operating on separate drums. The radius rod 
 has the brake shaft bearings riveted to it, so that all brake reac- 
 tions are taken on the radius rod. This radius rod is divided into 
 a front and rear part, each having a large threaded boss to re- 
 ceive the adjusting screw. This screw has right and left-hand 
 threads and is locked by lock nuts. The front end of the rod is 
 divided on the jack-shaft center and is provided with a spherical 
 surface to give universal movement. 
 
140 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 An enclosed chain drive is illustrated in Fig. 118. This con- 
 struction has been used on the Natco one-ton trucks for several 
 years. The case is cast in two parts and well ribbed, so that it 
 can be used as the radius rod also. The forward end carries the 
 adjusting member, which is in the form of an eccentric and pro- 
 
 ECCENTRIG ADJ. MEMBER. 
 
 FIG. 118. Enclosed Chain Drive. 
 
 vides a spherical bearing to obtain universal action. The rear 
 end pivots about the brake drum, in which are mounted double 
 expanding brakes. The rear wheel hub and brake drum are cast 
 in one piece to obtain proper strength for this construction, since 
 the thrust is transmitted through the brake drum. Ground joints 
 are used to prevent oil leaks, while drain plugs are also provided 
 so that the case can be cleaned at intervals. 
 
 The advantages of the chain drive are low cost of changing 
 gear ratios, minimum unspring weight, somewhat greater flexibil- 
 ity, mounting of differential on chassis, where it is protected by 
 the vehicle springs, and greater accessibility, for broken links can 
 be repaired easily. When it is kept clean, oiled and properly ad- 
 justed it is a very efficient means of power transmission ; however, 
 this is quite a difficult problem. This naturally suggests enclosed 
 chain drives which operate in oil ; however, a practical chain case 
 is a difficult problem, so that many joints and bearings are nec- 
 essary, which are subject to frequent renewal and in service the 
 chain case soon becomes more noisy than the open drive. It also 
 makes a somewhat inaccessible construction, thus increasing main- 
 tenance cost. 
 
 The Bevel-gear Axle. The bevel-gear axle is almost univer- 
 sally used on pleasure cars. However, it is not very popular on 
 commercial cars, being used only on the light vehicles of capaci- 
 ties up to 1,500 Ibs. Its use is limited, owing to that it is very 
 
THE FINAL DRIVE 
 
 141 
 
 difficult to provide a higher reduction than four or five to one 
 without sacrificing road clearance. 
 
 Fig. 119 depicts the G.M.C. 1,500-lb. delivery car bevel drive 
 rear axle, which is of the three-quarter floating type. The axle 
 housing is divided into two halves having tubes riveted into it, 
 w T hich extend slightly beyond the wheel bearing. The differential 
 is of the bevel-gear type and mounted on Hyatt roller bearings 
 
 TUBE YOKE 
 
 FIG. 119. G.M.C. Delivery Car Bevel Gear Type Rear Axle. 
 
 inside of the axle housing. Ball thrust bearings with ample ad- 
 justment are mounted on each side of the Hyatt roller bearings 
 to take up the thrust load of the gears. The hub is provided with 
 a Hyatt bearing, which is centered under the wheel and is re- 
 tained by a threaded retaining member which has a funnel-shaped 
 part formed integral to throw off the oil and prevent it from 
 reaching the brakes. The hub is keyed to axle shaft, so that the 
 weight is carried on the housing tube, while the shaft transmits 
 the powder. The spring seat swivels upon the brake spider, which 
 also carries the ends of the truss rod. The axle housing has a 
 bracket to support the brake shafts, so that the levers can be 
 mounted close to the center of the axle. The brakes are of the 
 internal and external type and operate on pressed steel brake 
 drums bolted to the wheels.. The propeller shaft is enclosed in 
 the torque tube, which is bolted to the axle housing and carries 
 the ball bearings for supporting the bevel pinion, while the pin- 
 
142 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 ion shaft and the propeller shafts have squared ends and are con- 
 nected by a sleeve having a square hole fitting over the squared 
 shaft ends. 
 
 The torque is taken by the torque tube through a large fork, 
 which is hinged to a heavy cross member, while the spring is free 
 at both ends. Radius rods, running from the brake spider diag- 
 onally to a point directly back of the torque tube fork, take up 
 the thrust load. 
 
 Bevel gear drive axles of similar construction are also on the 
 Steward, Commerce, Vim and other light delivery cars. They 
 are mostly used with pneumatic tires, where speed is a factor. 
 
 Types Intended to Overcome Reduction Difficulties. The dif- 
 ficulty with the bevel-gear axle is overcome in the double reduc- 
 tion, internal gear and worm-gear axles. The double reduction 
 and the internal gear type use two reductions, one by bevel gears 
 and the other by spur gears, while in the worm-gear axle a large 
 reduction can be obtained with a single pair of gears. 
 
 The advantages claimed for the double reduction are silent 
 operation, enclosure of all working parts, while the differential 
 bearings are relieved of thrust loads. By mounting one pair of 
 gears above the other, approximately straight-line drive can be 
 obtained. 
 
 The internal gear-drive axle possesses the advantages of silent 
 operation and enclosed working parts. However, the differential 
 bearings are subjected to thrust loads, since the spur gears are 
 mounted in the wheel, and it is also difficult to obtain a straight- 
 line drive. They possess an advantage in that this axle is divided 
 into two units, the jack shaft which transmits the power and the 
 dead rear axle which carries the weight. The jack shaft is sim- 
 ilar to the chain drive jack shaft and may either be bolted to the 
 front or rear of the dead axle. 
 
 The worm-gear axle is probably the most simple construction, 
 since it has the least number of parts, can easily be arranged for 
 straight-line drive, and possesses the features of silent operation, 
 protection of parts subject to wear and a wide range of gear 
 ratios can be provided without changing the distance between 
 the worm and the wheel. 
 
 All types of shaft- driven axles can be made quite accessible 
 so that maintenance can be held within reason. The double re- 
 duction and worm-gear axles are generally of the full floating 
 type, in which the weight is carried on the axle tubes and the 
 shafts are subject to only torsional stresses, as they only transmit 
 power. 
 
THE FINAL DRIVE 
 
 143 
 
 The Double-reduction Axle. One of the first commercial car 
 builders to use a shaft-drive axle was the Autocar Company, 
 which equips all of its models with double-reduction axles. Ex- 
 tensive refinements have been made on this axle and it presents an 
 
 FIG. 120. Double Reduction Axle used on the Autocar. 
 
 excellent type of double reduction. This axle is shown in Fig. 
 120, and is what is termed a full-floating axle. The bevel gears 
 are placed above the spur gears so that a straight drive can be 
 
 FIG. 121. Weston-Mott Double Reduction Axle. 
 
 obtained, while it also has an advantage in machining the bevel 
 gears, since they are much smaller than they would be if they 
 were used instead of spur gears for the final reduction. The spur 
 gears are better able to take care of the torque of the second re- 
 duction and the differential bearings are relieved of the high 
 
144 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 thrust loads, which they would be required to carry if bevel gears 
 were used. 
 
 The axle housing proper is cast in two halves joined together 
 at the center. The spring seats are cast integral and the end of 
 the housing is provided with a flange to which the brake spider 
 is bolted. A reinforcing tube is placed into the housing, which 
 extends a little beyond the spring seat, the end of which carries 
 the wheel bearings. The bevel and spur driving gear and dif- 
 ferential are mounted in a unit in the differential carrier and 
 bolted to the housing proper. The drive shafts have splined 
 ends and the wheel drive is taken through flanges bolted to the 
 hub. Internal and external brakes are mounted on the brake 
 drums inside of the wheels. 
 
 FIG. 122. White 1J Ton Double Reduction Axle with Helical Cut Spur 
 
 Gears. 
 
 Fig. 121 illustrates a double-reduction axle of one-ton capacity, 
 which was placed on the market several years ago by the Weston 
 Mott Company, and was used on the Menominee, Flint and other 
 light commercial cars. This axle is also of the full floating type, 
 but differs from the one described above in that straight-line 
 drive cannot be obtained since the bevel gear set is mounted in 
 front of the spur gear set instead of above it. The differential 
 
THE FINAL DRIVE 
 
 145 
 
 f 
 
 carrier has an extension on each side into which are placed the 
 axle tubes, while a large cover is provided for inspection pur- 
 poses. The brake spider has a hub which is keyed to the axle 
 tube and upon which the spring seat can pivot, while the brake 
 operating levers are also brought inside of the frame. The drive 
 for the wheel is through a jaw clutch, the male member of which 
 is forged integral with the drive shaft, while the female member 
 is formed integral with the hub. 
 
 The Autocar is designed to take both torque and thrust 
 through the spring, while the Weston Mott axle may be arranged 
 with radius rods to take the thrust load and a torque arm to take 
 the torque load. 
 
 The one-and-one-half ton White truck is also equipped with 
 a double-reduction axle (Fig. 122) which differs from the above 
 in that the bevel gears are in the customary place as in the pleas- 
 ure car axle. The propeller shaft carrying the spur pinion which 
 has helical teeth, is mounted above the short shaft carrying the 
 helical spur gear and bevel pinion. Both shafts are supported by 
 ball bearings at each end and provision is made to take care of 
 the thrust of these gears. This presents another method of ap- 
 proximately a straight-line drive, while the torque is taken 
 through the springs and the driving thrust by radius rods. 
 
 The double-reduction drive, like the worm drive, will be 
 found on both gasoline and electric vehicles, although its use 
 seems to be mostly on vehicles of 5,000 Ibs. capacity and under. . 
 
 The Internal-gear Drive. As mentioned above, the internal- 
 gear drive axle is really a double reduction, in which two sets of 
 gears are used. It is also similar to the chain drive in that a jack 
 shaft and dead rear axle are used. However, the two units are 
 
 BRAKE DRUM 
 SPRING SEAT 
 
 DEAD AXLE 
 
 1 
 
 PROPELLER SHAFT 
 BRAKE: 
 
 FIG. 123. Fremont Mais Internal Gear Axle. 
 
 11 
 
146 MOTOK TEUCK DESIGN AND CONSTRUCTION 
 
 bolted together and the sprockets and chains are replaced by in- 
 ternal gears in the brake drums and spur pinions on the drive 
 shafts. Among the users of this type of axle may be mentioned 
 the General Vehicle Company, Fremont Mais, Mais, Denby, Re- 
 public, Stewart and numerous others. 
 
 Fig. 123 serves to illustrate the Fremont-Mais one-and-a-half- 
 ton axle, showing a dead rear axle of I-beam section with integral 
 spring seats and spindles carrying a bronze sleeve and a double 
 row ball bearing upon which the wheel is mounted. The jack- 
 shaft unit, carrying the differential, drive shafts and bevel driv- 
 ing gears, is mounted to the rear of the I-beam axle. The hous-- 
 ing of this unit is riveted to the axle and supports tubes which 
 enclose the drive shafts and extend into the brake spider to sup- 
 port the wheel brakes. The drive shafts float in the differential 
 and are supported inside the brake spider by a double row ball 
 bearing next to the spur driving pinion. The hub flange is made 
 large enough so that the brake drum can be riveted to it, while 
 inside the brake drum and bolted to the hub is the internal gear. 
 The driving gear, with its bearing, is enclosed in a separate com- 
 partment formed by the brake drum, spider and hub and works 
 in a bath of oil. One set of brakes is located in the wheel drums 
 while the other is mounted on the bevel pinion shaft and sup- 
 ported from the rear axle. This brake acts on both wheels 
 through the driving unit. 
 
 Fig. 124 depicts the massive construction of the Studebaker 
 internal gear drive rear axle which possesses several unique fea- 
 tures, having a dead rear axle on which are mounted the bevel 
 gear differential and drive shafts which comprise the jack shaft, 
 while the wheels are driven through spur pinions meshing with 
 internal spur gears. The whole mechanism is enclosed and felt 
 packings are provided to keep out dust and retain grease and oil 
 in the various compartments. 
 
 The principal difference between this axle and that above is 
 the scheme of the brakes. In front of the bevel gears housing is 
 a very wide brake drum on the bevel pinion shaft. On this drum 
 are the two brake bands for foot and ratches hand brakes, but an 
 additional hand emergency brake is provided not ratchet re- 
 tained. It consists of shoes acting upon V-shaped ribs running 
 around on the outside of the internal gears on the rear wheels 
 close to the spokes. It is claimed that this construction relieves 
 all brakes from any danger of slipping due to leakage of grease 
 around the rear wheels and yet provides a brake acting upon the 
 
THE FINAL DEIVE 
 
 147 
 
 FIG. 124. Sttfdebaker Internal Gear Drive Axle. 
 
 FIG. 125. Russell Internal Gear Axle. 
 
148 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 rear wheels themselves in case any breakage should put the regu- 
 lar brakes out of commission. 
 
 With this axle, triangular channel shaped pressed members 
 which are bolted to the brake spiders and hinged to a heavy 
 
 cross member take up the 
 thrust and torque loads. 
 
 The G. V. Mercedes 
 gasoline trucks are also in- 
 ternal gear driven. While 
 they are similar in some 
 respects to the Studebaker 
 construction, the axle is 
 equipped with only one 
 set of brakes, while the 
 other brake is mounted in 
 back of the transmission. 
 They also use the trian- 
 gular pressed steel mem- 
 bers for taking torque and 
 thrust loads, but. have a 
 cross member located di- 
 rectly in front of the jack 
 shaft and bolted to it, and 
 the triangular members. 
 
 The Eussell internal 
 gear-drive axle illustrated 
 in Fig. 125 has a forged 
 steel dead axle of round 
 section with spring seats 
 keyed to it so the torque 
 and thrust can be taken on 
 the springs. The axle is 
 similar to those mentioned 
 above. 
 
 There is one feature 
 about the internal gear in 
 that it employs two reduc- 
 tions as mentioned above 
 and is similar to the chain 
 drive. The first reduction is through bevel gears and is such that 
 a low torque is transmitted by the rapidly revolving drive shafts, 
 
THE FINAL DRIVE 
 
 149 
 
 which permits a light structure for the driving unit. The next 
 reduction, of course, is near the wheels and supported directly 
 by them. The reduction in the wheels is such as to provide a high 
 torque direct to the wheels. By making the jack shaft a high- 
 speed unit, considerable weight can be saved. However, it has 
 a greater unsprung weight than the chain drive. 
 
 The Torbensen axle shown in Fig. 126 is also of the internal 
 gear type. The dead axle is a one-piece drop forging of I-beam 
 section, with chrome vanadium spindles and fixed spring seats. 
 The cylindrical end of the dead axle is of large diameter, and ex- 
 tends nearly to the center line of the spokes, so that the bending 
 moment of the spindle is reduced to a minimum. All members of 
 the jack shaft are enclosed, affording cleanliness, efficient lubrica- 
 tion and quiet working. 
 
 FIG. 127. Clark Internal Gear Driven Eear Axle. 
 
 The Clark axle (Fig. 127) is another type of internal gear- 
 drive axle, with a load carrying member of round section. A 
 feature of this axle is that all parts are identical, there being no 
 rights and lefts. The driving, unit is located in front of the load 
 carrying member and instead of supporting at the center, the 
 driving unit is supported at each end from the integral spring 
 seats and brake spider. The differential and drive shafts are 
 supported on Hyatt roller bearings and ball thrust bearings, 
 while the wheels are supported on double row ball bearings. 
 
 The White 3- and 5-ton trucks are equipped with a combina- 
 tion double reduction and internal gear-drive axle. This axle 
 (Fig. 128), called a double-reduction drive, but in reality an in- 
 ternal gear drive, has a floating rear axle concentric with the 
 
150 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 axle housing. The power from the propeller shaft is trans- 
 mitted to the usual bevel gear set and differential which in turn 
 drive the axle shafts. These shafts have spur pinions mounted 
 
 FIG. 128. New Type of Double Eeduction and Internal Gear Drive Axle 
 used on White 3 and 4 Ton Trucks. 
 
 inside the hub case which mesh with another spur pinion which 
 in turn meshes with the internal gear bolted to the hub of the 
 wheel. By this method of applying the power to the wheel, a 
 
 FIG. 129. Fierce-Arrow Worm Drive Axle. 
 
 second reduction is obtained between the three gears in the hub 
 case very much like the reduction which takes place between the 
 sprocket wheels of a chain drive. 
 
THE FINAL DEIVE 
 
 151 
 
 The Worm Drive. In spite of bitter opposition, worm drive 
 has made great strides during the past year, quite a number of 
 makers having added worm-driven models to their line, good 
 axles of this type being obtainable. Several of the older com- 
 panies are building their own axle, amongst these being the 
 Pierce, Packard and Locomobile companies, the former adding a 
 two-ton model, while the latter have recently announced three- 
 and four-ton models. 
 
 Fig. 129 will serve to illustrate the Pierce axle which is of the 
 full-floating type, with the worm mounted above the wheel. The 
 worm, worm wheel and spur gear differential are mounted on ball 
 bearings and assembled as a unit with the cover. This construc- 
 tion permits the removal of the entire unit without disturbing 
 the balance of the axle, as shown in the illustration. The hous- 
 ing is a heavy steel casting reinforced by tubes which carry the 
 wheel bearing and extend beyond the spring seats. The emer- 
 gency brakes are mounted in the rear wheels and the service brake 
 is located back of the transmission. Thrust is taken on radius 
 rods and the torque load on a heavy torque arm. The road wheel 
 is driven through a squared shaft and driving flange bolted to the 
 hub. 
 
 The worm-drive axle recently introduced by the Locomobile 
 Company is illustrated in Fig. 130, and is also of the full-floating 
 type. However, it differs from the above in that a bevel-gear 
 
 DUAL TIRE 
 
 THRUST BEARING 
 
 BRAKEDRUM 
 
 FTG. 130. Riker Worm Drive Axle. 
 
 differential is used, while the housing is divided into three parts, 
 consisting of a center housing and two ends which are bolted 
 together. Reinforcing tubes are also used, which carry the 
 
152 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 wheel bearings and extend to points just outside the differential 
 bearings. The ends of these carry a series of packing washers 
 to prevent the oil working out onto the brakes. The outer ends 
 of the housing have spherical bearings for the radius rods, while 
 the spring seats pivot on bronze bushings. The spring is mounted 
 outside the frame while the radius rods are placed directly under 
 the side frame members. The worm is mounted above the wheel 
 and, together with the differential and bearings, forms a unit 
 with the cover. A heavy truss rod is anchored to the housing 
 
 FIG. 131. Timken Worm Drive Axle. 
 
 inside the brake drum and provided with a turnbuckle for adjust- 
 ment. The wheels are mounted on Timken heavy roller bear- 
 ings, while the driving unit is mounted on ball bearings and pro- 
 vided with suitable thrust bearings. The drive shafts are of the 
 ten-spline type, and drive the wheels through flanges bolted to 
 the wheel hubs. Attention might be called to the method of re- 
 ducing the weight, by lightening the reinforcing tube. The inner 
 wall of this tube tapers from the end to the center of spring 
 seat, from this point to just inside the inner- wheel bearing where 
 the greatest load comes. 
 
 The Timken David Brown axle used in a number of commer- 
 cial cars is depicted in Fig. 131, being similar in construction to 
 those described above, with the worm, worm w T heel, differential 
 and their bearings assembled into a unit with the cover. How- 
 ever, in this axle the well-known Timken bearings are used 
 throughout, and, owing to their ability to carry thrust loads, it 
 is claimed no thrust bearings are necessary. To the writer's 
 knowledge this company is the only one resorting to roller bear- 
 ings for mounting of the worm. The flange for driving the 
 wheels is forged integral with the drive shaft, while the general 
 construction is along conventional lines. 
 
THE FINAL DRIVE 
 
 153 
 
 Another worm-drive axle used by several commercial car 
 builders is the Sheldon axle (Fig. 132). It is also constructed 
 along conventional lines, having the differential and worm gear 
 a unit. However, it is of the semi-floating type, and the housing, 
 which is cast in one piece, is so arranged that either over or 
 underslung springs may be used. As the axle is of the semi- 
 
 FIG. 132. Sheldon Worm Drive Axle Semi-Floating Type. 
 
 floating type, the housing is made of liberal proportion and the 
 weight is carried on the drive shaft, while a ball bearing is 
 mounted inside of the wheel which is attached and driven by 
 means of a long taper 'and key. This is clearly shown in the illus- 
 trations. The features of semi-floating axles can perhaps be best 
 described by comparing with the full-floating and three-quarter- 
 floating types. 
 
 FIG. 133. Phantom View of Packard Worm Drive Axle. 
 
154 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 The Packard worm-drive axle (Fig. 133) also has a three- 
 piece housing, with the differential and driving unit mounted in a 
 unit with the cover. The differential is spur-gear type, and the 
 entire driving unit is mounted on ball bearings and provided with 
 suitable thrust bearings. As in the construction described above, 
 the worm is mounted above the wheel. The housing is massive 
 steel construction, well ribbed to provide maximum strength. 
 The entire construction is arranged for straight-line drive from 
 the transmission through two universals, while the thrust is 
 taken by radius rods and the torque by a heavy torque arm. 
 
 Rear Axle Types. Shaft-driven commercial car axles may 
 be classified according to the arrangement of the wheel bearings. 
 If the end of the drive shaft next to the wheel has a bearing 
 directly upon it, the axle is then classed as semi-floating type. 
 This type of axles possesses some advantages in cost of manu- 
 facture and simplicity, and is the lightest axle for its strength. 
 
 The great strains imposed upon the bearings and housing of 
 the full-floating type in skidding against obstructions are much 
 less in the semi-floating type, because of 'the greater distance 
 between bearings. However, there is much difference of opinion 
 as to the relative advantages of the various types of axles. 
 
 In the semi-floating axle, the drive shaft carries the weight 
 of the vehicle and must also resist torsional strain. 
 
 In order to make an axle in which only torsional driving 
 strains are imposed upon the drive shaft thus approximating 
 some advantages of the dead rear axle a construction is used 
 wherein each wheel is mounted outside the axle housing, and the 
 drive is taken through a central shaft connected to the hub by 
 either a jaw clutch or flange bolted to the hub. This is known as 
 the full-floating type of axle. It has the advantage of having 
 the axle shaft free from all lateral strains, thus greatly reducing 
 the danger of breakage and of bending, the latter causing the 
 wheel to wabble. Even if the shaft is broken, the wheel is still 
 securely mounted on the axle housing, so that the axle does not 
 drop to the ground. The construction is such that the drive 
 shafts can be withdrawn and even the differential dismounted 
 without removing the wheels from the axle, or the axle from the 
 car. 
 
 The jaw clutch for driving the wheel has the advantage of 
 being more easily withdrawn from the axle and affords more 
 freedom to allow for misaligning parts, while the flange drive 
 
THE FINAL DEIVE 155 
 
 removes all chances of noise sometimes made by jaw clutches, 
 and is claimed to be sligthly less expensive to construct. 
 
 The three-quarter-floating axle is a compromise between the 
 semi-floating and full-floating types. It has the wheel mounted 
 on a single bearing outside the axle housing on a reinforcing 
 tube, and kept in alignment by being rigidly attached to the 
 driving shaft by either a key, as in the semi-floating type, or a 
 flanged connection as in one style of full-floating axle. Accord- 
 ing to the type of bearing employed at the wheel, the axle shaft 
 is held in place either by the wheel bearing or by some sort of a 
 lock near the differential. 
 
 As in most compromises, this type possesses some of the ad- 
 vantages of each of the others. No dead load is placed on the 
 axle shaft, but the skidding strains are little, if any, different on 
 the bearings and shafts than with the semi-floating type. As in 
 the semi-floating axle, any type of bearing can be used, and the 
 weight may be less than the full-floating axle. When the wheel 
 bearings are of a type suitable to take end thrust, they are usually 
 so mounted as to hold the wheel in place on the axle end, and the 
 shaft is connected by a flange. The shaft can then be removed 
 without disturbing the wheel. 
 
 Worm and bevel-gear axles are similar to pleasure car axles, 
 and various parts of the other two types are also similar; how- 
 ever, while they are similar, their proportions are materially in- 
 creased to withstand vibration. 
 
 Method of Providing for Torsion and Propulsion in Shaft- 
 driven Commercial Cars. At the present writing there seem to be 
 about five methods of providing for torque and thrust loads on 
 shaft-driven axles, as follows: (1) torque and thrust through the 
 vehicle springs; (2) torque and thrust through triangular struc- 
 ture attached to a rigid cross member; (3) torque on springs, 
 thrust on radius rods; (4) separate torque and radius rod mem- 
 bers; (5) torque tube surrounding drive shaft and anchored to 
 the frame by a large yoke and triangular radius rods anchored to 
 the torque tube. 
 
 In a shaft-driven axle there are two separate torsional forces. 
 There is first, the primary torque of the drive shaft, and the sec- 
 ondary torque of the axle itself. The inertia of the axle causes 
 the shaft to react upon the gear set support in a tendency to 
 whirl them instead of itself turning, and the inertia of the wheels 
 on the road tends to cause the axle to whirl, instead of the wheels 
 
156 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 revolving. Owing to the reduction afforded by the gear set on 
 the lower gears, there is a certain amount of drive-shaft torsion, 
 even on a heavy vehicle. It is no greater, however, the motor 
 being of the same power as in a passenger vehicle, as a rule, and, 
 as in the latter, it can be transmitted directly to the frame, the 
 springs being the medium relied upon to absorb it. 
 
 The axle torque offers the greatest problem. In some vehicles 
 the springs or the ordinary form of torque arm supported from 
 the frame have proven successful, while in other cases torsion is 
 provided for by connecting the sub-frame, upon which the com- 
 plete power plant and transmission system are mounted, to the 
 rear axle at one point and to the forward part of the frame on 
 two points. Propulsion may be through the swinging sub-frame, 
 torque tube, springs or radius rods. When radius rods are used, 
 the springs are shackled at both ends, and when the thrust is 
 taken through the springs the front end is rigidly attached to the 
 frame and the rear end is shackled. 
 
 There seems to be a very wide difference of opinion as to the 
 relative merits of .the various methods, and examples of each 
 type may be found with either type of axle. The method of tak- 
 ing stresses on the springs, which is termed the Hotchkiss drive, 
 has been quite popular on the lighter vehicles and at the present 
 there seems to be a general tendency to apply it to the heavier 
 vehicles also. The separate torque and radius rod construction is 
 also used on a number of heavy worm-driven vehicles. 
 
 TT 
 
 "TT 
 
 FIG. 134. Arrangement of Springs for Taking- Torsion and Thrust. This 
 is called the Hotchkiss Drive. 
 
 The internal gear-driven vehicles are divided between Hotch- 
 kiss drive and triangular members anchored to the frame cross 
 member for taking up these stresses. The double reduction seems 
 to favor the worm practice, as both of these methods are found, 
 while the bevel drive seems to favor pleasure car methods. 
 
THE FINAL DRIVE 
 
 157 
 
 Fig. 134 depicts the spring mounting for Hotchkiss drive, in 
 which both torque and thrust are taken by the springs. The front 
 ends of the springs are rigidly mounted in a heavy bracket at- 
 tached to the frame, while the rear ends are shackled in the usual 
 manner. The springs must be made with as little camber as pos- 
 sible, that is, the spring should be nearly flat under load, so that 
 the driving effort is applied lengthwise of the top leaf, the direc- 
 tion of the effort lying within the metal instead of across a chord 
 of the arc outside it. 
 
 FIG. 135. Diamond T-Spring Anchorage. 
 
 Springs for Hotchkiss drive must be especially designed to 
 take these stresses and require numerous rebound clips. 
 
 Some excellent features have been developed lately which 
 show how the problems connected with this type of drive have 
 been solved. Nickel steel U-boats are used by many, while others 
 are providing rigid anchoring of the springs to axle in various 
 ways. As flat springs must be used, this necessitates a rigid 
 anchorage to prevent the pressure blocks from creeping. 
 
 On the Diamond T-trucks particularly rigid anchoring of the 
 spring to the axle is used. This is shown in Fig. 135, and con- 
 sists of a special casting which is U-shaped and snugly fits the 
 spring. On top of this casting is a special block, which is re- 
 cessed to take an upward arch in the center of the top leaf of the 
 spring. On the vertical sides of the U-casting are heavy shoulders 
 
158 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 FIG. 136. Torque taken on Springs. Driving Thrust taken on Radius Rods. 
 
 FIG. 137. Triangular Torque and Radius Rods Applied to Internal Gear- 
 Drive Axle. 
 
THE FINAL DRIVE 
 
 159 
 
 bearing against the clips or U-bolts and so preventing displace- 
 ment of these. This feature of keeping the clips at right angles 
 to the spring leaves is an essential of this type of drive. The 
 Winther trucks are provided with a similar arrangement, while 
 on the Military class B trucks the spring plates are provided 
 with spherical depressions which lock the spring plates and pre- 
 vent creeping. 
 
 Those makers who do not provide any special, anchorage give 
 special attention to have anchorage as rigid as possible with the 
 use of a specially flat spring with heavy upper leaves. Spring 
 
 FIG. 138. Separate Torque and Baclius Rods. 
 
 seats are usually machined to the center of the spring and all 
 points of contact are carefully white-leaded so that both air and 
 water are kept out of the joints. 
 
 On the new G. M. C. worm-driver trucks, the springs are 
 shackled at both ends and take the torque load, while radius rods 
 are used to take the driving thrust as shown in Fig. 136. 
 
 Fig. 137 illustrates the method of taking these stresses on 
 tubular rods forming a triangular construction with the rear 
 axle. The tubes are rigidly attached to the brake supports at the 
 rear, and form a large ball at the forward end, which is mounted 
 in a spherical bearing on the frame cross member, directly over 
 or under the universal joint. This construction will be found on 
 several internal gear models. 
 
160 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 The dotted lines in this illustration show another type of 
 triangular torque and radius rods. However, each rod is hinged 
 separately on each side of the universal joint to the frame cross 
 member. This construction is used on the Studebaker and G.Y. 
 internal gear-driven vehicles and the Flint double reduction drive 
 and others. 
 
 Separate torque and radius rods are used on the Pie'rce, Loco- 
 mobile, Packard and other dorm-driven models, and the Menomi- 
 nee double-reduction drive, the latter being shown in Fig. 138. 
 The torque rod is a pressed-steel channel-shaped member, having 
 a ball end, which is mounted between springs in a bracket hinged 
 to the axle and frame side rails. 
 
 FIG. 139. Manly Method of Taking Drive and Torsional Strains. 
 
 On the Manly trucks, the radius rods (Fig. 139) are of pecul- 
 iar construction and in addition to taking the torque and driving 
 strains also maintain the axle in correct relation to the drive 
 shaft, thus releasing the rear universal joint of any irregularity. 
 Connection from the frame to the axle is made by means of a pair 
 of rods on each side, the rods of one pair being placed above the 
 other and pivoted at both the axle and frame ends. The driving 
 force passes through both rods, being taken from a point under 
 the springs and in line with the axle center to a heavy steel 
 bracket on the frame. The tendency for the axle housing to 
 rotate, which it is a natural result of the reaction of the wheels in 
 driving, is resisted by these pairs of rods. This torque reaction 
 compresses one rod and pulls on the other and because of their 
 pivoted mounting it is impossible to place a binding strain on 
 either rod. The upper and lower rods on each side of the chassis 
 are not quite parallel with each other, their distances apart front 
 and rear, being so proportioned that the rear axle itself is caused 
 to move in a curve that would result from an ideal condition of 
 having radius rods as long as the propeller shaft tube and having 
 their front pivots in line with the front universal. Deflection 
 of the rear universal is thus entirely done away with. 
 
THE FINAL DRIVE 161 
 
 With bevel-drive axles there are several methods in use, which 
 follow pleasure-car practice closely. The torque tube may either 
 surround the drive shaft and the drive be taken through the 
 spring and the radius rod, as in the Commerce, Vim and others, 
 or the torque and thrust may be taken through a torque tube and 
 radius rod hinged to the cross member, as advocated by the 
 G.M.C. 1,500-lb. delivery car, which is illustrated in Fig. 119. 
 
 There are various arguments which can be advanced for either 
 of these constructions, while each type seems to have its share of 
 support amongst the manufacturers. From the writer's ob- 
 servations it seems to be the general tendency to let the springs 
 perform these functions in the lighter vehicles, and to use radius 
 and torque rods and combinations of these on the heavier models. 
 
 12 
 
CHAPTEK XI 
 
 FEONT- AND FOUR-WHEEL DRIVES 
 
 IN the foregoing chapters on the final drive, we considered 
 all types of final rear wheel drives. There are also a number of 
 commercial cars, in which the final drive is through the front 
 wheels, and others in which it is through all four wheels. Both 
 of these types have gained considerably in popularity of late. 
 This is possibly due, to some extent, to the ' demands of the 
 various war departments, for motor-driven vehicles, which can 
 propel themselves to any point where mules can pull a wagon. 
 
 This same ability is also of great importance in many other 
 classes of service, where departure from the road surface is some- 
 times necessary. It is especially of importance to coal dealers, 
 who are generally called on to make deliveries in narrow alleys; 
 excavating contractors, who must haul material in and out of 
 excavations, building supply concerns, handling such as lumber, 
 gravel, brick, etc., over unpaved roads and sometimes across 
 swampy land to deliver the material to the building site. There 
 are also other cases to which the four-wheel drive is adaptable. 
 
 There is also a variety of cases in which extremely low bodies 
 are necessary, as in hauling long structural girders, timbers and 
 heavy stone. On the other hand, there are such problems as 
 handling light paper, boxed paper and tin cans and tubes and 
 other articles which present a very bulky load. For these pur- 
 poses, the front-wheel drive lends itself to best advantage, while 
 it is also of considerable advantage for fire apparatus, etc., where 
 it is desired to retain the vehicles used with the horse equipment. 
 
 Foreign manufacturers were the first to experiment with these 
 types of vehicles and have perhaps led the way; however, there 
 are a number of companies in America, which are prepared to 
 manufacture these types of vehicles. As the front-wheel and 
 four-wheel drives are closely related, and practically involve the 
 same mechanical problem in driving and steering, they will be 
 considered together. 
 
 Four Methods of Drive. In comparing the various designs 
 we find four methods of driving and two methods of steering. 
 In the first construction, the whole axle pivots about its center 
 
 162 
 
FKONT- AND FOUR-WHEEL DRIVES 
 
 163 
 
 and the wheels are driven, as in the ordinary dead or live rear 
 axle. This construction is mostly used with front-drive units, 
 that is, in vehicles propelled through the front wheels only. In 
 the second type, the axles have steering knuckles, as in the con- 
 ventional type, but the flexibility is obtained through universal 
 joints or chains driving the wheels through internal gearing. 
 In the third type, the wheels are driven through bevel gears 
 mounted inside the wheel and on the steering knuckles, another 
 pair of bevel gears mounted on the steering knuckles driving the 
 wheels, through shafts extending from the central pair of gears 
 in the axle housing. These three are termed mechanical drives; 
 while the fourth construction is a non-mechanical drive, electric 
 motors being mounted in the wheels and driving direct through 
 reduction gearing. 
 
 The front-wheel drives, in some cases, are so constructed that 
 this forms the power unit, which may be attached to any type of 
 vehicle the user may desire, while a rear frame construction, upon 
 which any type of body can be mounted, may also be provided. 
 With the latter, the rear wheels may be shod with steel or rubber 
 tires as desired. The Devon, Pull-More, and Meyers may be men- 
 tioned as examples of this type. 
 
 Whole Front Unit Pivoting Chain Drive. Referring to Fig. 
 140, illustrating the Devon Tractor Trailer, the engine is mounted 
 
 u-e 
 
 FIG. 140. Plan View of the Devon Tractor. 
 
164 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 in front of the axle and placed lengthwise. It is located toward 
 the left side and enclosed by a metal hood. At the rear of this 
 hood is the vertical steering column, and back of this, a metal 
 seat. The power from the engine is transmitted to the clutch 
 and transmission at the rear, the transmission being a unit with 
 a jackshaft, as in the ordinary chain-driven truck. The front 
 axle is similar to the ordinary dead rear axle, and carries a set 
 of brakes and sprockets. From the jackshaft, the power is trans- 
 mitted to the front wheels through chains, which are enclosed. 
 In steering, the entire unit is turned bodily by means of the steer- 
 ing wheel, through bevel gears, rotates a worm, engaging the cir- 
 
 FIG. 141. The Meyers Tractor. 
 
 cumference of a large worm wheel attached to the forward part 
 of the main frame and concentric with the pivot. This worm is 
 mounted on a splined shaft, between heavy coil springs to absorb 
 the road shocks. 
 
 The Pull-More front drive is similar to the above; but has a 
 power steering device operated by the engine, this steering device 
 working through a sprocket on the crankshaft, which, by means 
 of a chain, drives a countershaft, located in the lower half of the 
 crank case. This countershaft operates the arm of the steering 
 reach, which is a part of the king bolt. This king bolt is located 
 midway between the front wheels, and forms the axis upon 
 which the entire front unit revolves. Differentials are provided 
 to permit right-and-left-hand steering. An ordinary steering 
 post and wheel is used to operate the power steering device. 
 
FKONT- AND FOUE-WHEEL DKIVES 
 
 165 
 
 The Meyers front drive (Fig. 141) is similar to the above 
 types, in that the engine is placed forward of the front axle. 
 The power of the motor is transmitted from the jackshaft, through 
 
 FIG. 142. Side and Plan View of Walter Transmission and Front-Wheel 
 
 Drive. 
 
 side chains, to a shock absorbing bracket, carrying another 
 sprocket attached to a short shaft, on the opposite end of which 
 
166 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 is a small gear, meshing with a large internal gear, bolted to the 
 spokes of the wheels. The main frame is mounted upon semi- 
 elleptic springs. The upper frame, which forms the pivoting 
 member, has a detachable castor-like wheel and as the weight is 
 to the rear of the unit, it is perfectly stable and can be driven 
 from place to place. The vehicle is steered by means of a circular 
 rack and pinion, upon a fifth wheel. The shock of starting is 
 eliminated by a patented arrangement on the driving pinion. 
 This pinion is mounted on an arm pivoted by the axle and is 
 free to roll in the internal gear to a slight extent, its forward 
 motion being limited by a positive stop and its rearward motion 
 by the rod and spring shown. 
 
 Gear Drive. In the types described above, the power is trans- 
 mitted to the wheel by means of roller chains. In the Walter 
 truck the power- is transmitted by shafts and internal gears, along 
 lines similar to the Latil front-drive trucks, built in France. The 
 transmission of the Walter is mounted with the engine, to form 
 a unit power plant, which is so located that the flywheel is just 
 in front of the front axle, the entire engine overhanging the axle. 
 From the sectional view of the transmission (Fig. 142), it will be 
 noted that the differential and bevel driving gears are mounted 
 at the front end of the secondary shaft, which is placed above 
 the main shaft. From the differential, extends two universally 
 jointed shafts to spur gear pinions on the steering knuckles, 
 which mesh with internal gears bolted to the front wheels. There 
 is no mechanism whatever back of the driver's seat, and the con- 
 struction is very compact. 
 
 Four-wheel Drive. The layout is such that the front-drive 
 unit does not have to be altered or changed in any way on vehi- 
 cles, which drive the rear wheels also, the forward unit of the 
 front drive being identical with the front unit of the four-wheel 
 driven vehicle. The secondary shaft of the transmission is ex- 
 tended back to another differential and bevel driving unit, 
 mounted on a frame directly over the rear axle. This unit also 
 has universal jointed shafts, extending to the rear steering 
 knuckles and carrying spur pinions, which mesh with internal 
 gears bolted to the rear wheels. 
 
 The rear axle is also used for steering in the four-wheel drive, 
 but not in the front drive. 
 
 The conventional type of worm and gear-steering column is 
 used, with a longitudinal cross-shaft, having a universal joint at 
 
FEONT- AND FOUR-WHEEL DRIVES 
 
 167 
 
 its forward: end. The rear end of this shaft carries a steering 
 arm, which is connected with the usual linkage to the rear wheels, 
 as shown in Fig. 143. 
 
 FIG. 143. Plan of the Walter-Four- Wheel Drive Chassis. 
 
 The Nash Quad and Duplex four-wheel drive trucks are also 
 driven by means of internal gears and universal- jointed shafts. 
 The wheel construction of the Nash Quad is shown in Fig. 144. 
 The propeller shafts are 
 
 driven from the secondary I rZ IL, 
 
 shaft of the transmission. 1 1 A^TTiHffl _r~~ "ZL 
 
 The cross-shafts, which 
 drive the wheels, are lo- 
 cated above the axle, while 
 the axle carries the weight 
 only and has the driving 
 gear and differential unit 
 bolted to it. The driving 
 pinion meshes w r ith an in- 
 ternal gear, mounted in the 
 wheel. The wheels are cast 
 steel with integral rim, 
 hubs and brake drums. The 
 driving pinion is located 
 above the steering knuckle and driven through a universal joint, 
 the center of which is directly in line with the pivot center of the 
 knuckle. 
 
 FIG. 144. 
 
 Nash Quad Method of Driving 
 Four Wheels. 
 
168 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 Combined Chain and Shaft Drive. The Duplex is also driven 
 by means of internal gears in the wheels and universal joints 
 mounted directly over the steering knuckles, and with drive 
 shafts above the springs. However, the method of transmitting 
 the power to the wheels is somewhat different from that described 
 above. The transmission is of conventional design and built in a 
 unit with'the engine. Power is transmitted by shaft to a chain 
 case, attached to the frame at approximately its center. This oil- 
 
 FIG. 145. Duplex Four-Wheel Drive Chain Case. 
 
 tight chain case, Fig. 145, is the junction point, connecting the 
 front and rear axle drive shafts, the driving sprocket, by means 
 of a silent chain, delivering power to the sprocket, to which the 
 fore and aft shafts are attached. The shaft, on which the driving 
 sprocket is mounted, carries a brake drum, which forms the service 
 brake, acting on all four wheels. Emergency brakes are on the 
 rear wheels. The vehicle is steered by the front wheels only, in 
 the usual manner. 
 
 Live-axle Drives. Another type of four-wheel drive construc- 
 tion is that employing a live front and rear axle ; that is, an axle 
 which both propels the car and carries the weight of the vehicle 
 and load. The F.W.D. and Nevada trucks are of this type. 
 
 In the F.W.D. chassis, the transmission is centrally located 
 with a very broad, silent chain, which transmits the power to a 
 shaft parallel to and far enough to one side of the transmission 
 to permit proper clearance between the engine and propeller 
 
FRONT- AND FOUE-WHEEL DRIVES 
 
 169 
 
 shaft. Each of the two propeller shafts carries a brake drum, so 
 that the braking force is applied to all four wheels. Steering is 
 by the front wheels only, so that the rear axle is of conventional 
 full-floating design with bevel-gear drive, excepting that the dif- 
 ferential housing is located to the left of the axle center. 
 
 FIG. 146. F.W.D. Front Axle. 
 
 The steering-knuckle pivot of the front axle (Fig. 146) is in 
 the form of a spherical joint, which has two trunnions, one on the 
 upper side and one on the lower side, so that only a pivoting 
 action, instead of a universal action is obtained. A divided hous- 
 ing surrounds these joints, to which is bolted the spindle, upon 
 which the wheel revolves. This pivot and wheel spindle are hol- 
 
 FIG. 147. Nevada Front Wheel Drive. 
 
170 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 low and contain the drive shaft and universal joint. The center 
 of this universal is in line with the center of the wheel pivot and 
 the shaft from one end extends into the differential, while the 
 other end has a square, which fits into the flange that drives the 
 wheel. 
 
 In the Nevada, the steering is also by front wheels only. The 
 general application of the power to the front wheels differs some- 
 what from the above, although this design also employs full- 
 floating axles. In this vehicle, the differential in the axles is 
 located to the left of the center and the front axle has a somewhat 
 different power-transmitting device in the steering knuckle. 
 
 The steering knuckles (Fig. 147) are similar to the usual type, 
 consisting of a yoke at the end of the axle tube, through which 
 passes a king bolt, on which revolves a solid wheel spindle. On 
 the knuckle, which surrounds the king bolt, is revolvably dis- 
 
 FIG. 148. Couple Gear Electric Drive. 
 
 posed a double bevel pinion. The lower teeth of this bevel pinion 
 are engaged by a bevel at the end of the axle shaft, which is dis- 
 posed within the axle tube. The upper teeth mesh with a larger 
 bevel gear, this being fastened to a stub shaft extending through 
 the wheel to the outer edge of the hub. The end is squared and 
 engages the driving flange, which drives the wheel. 
 
 In the chain-driven vehicles, the thrust and torque are taken 
 by the conventional radius rods, while the remainder are divided 
 between spring and radius rod construction. This is also true of 
 differentials, as some use three and others two, in compensating 
 for the division of power between the wheels. 
 
FEONT- AND FOUE-WHEEL DEIVES 171 
 
 Electric Drive. The fourth type, or electric, is particularly 
 adaptable to one, two or four-wheel drives, and affords a very 
 simple construction mechanically. The Couple Gear Freight 
 Wheel Company makes a type of road wheel, which is constructed 
 from two steel discs, between which is mounted an electric motor. 
 This wheel (Fig. 148) can be attached to an axle, regardless of 
 whether or not it is pivoted. This company builds two types of 
 trucks, one straight electric and the other gasoline electric. In 
 the former, batteries are used to supply the current to the motors 
 in the wheels, while in the latter type, a gasoline engine drives an 
 electric generator, which furnishes the current consumed by the 
 motors, in driving the wheels. The motor is carried by the steer- 
 ing knuckle, the armature having a pinion at each end, one pinion 
 pulling up on one side and the other pulling down on the oppo- 
 site side and both mesh with large ring gears attached to the two 
 discs of the wheel, ^his affords a single reduction of twenty- 
 five to one. A device, which is termed an " evener," permits of 
 compensating movements and divides the force equally between 
 the two pinions, regardless of any unequal wear or adjustments. 
 
 Both front-wheel drives and four-wheel drives, are capable of 
 further developments, and, if demands for these types of vehicles 
 continue, we may expect to see considerable improvement in 
 details. 
 
CHAPTEE XII 
 
 MOTOR TEUCK BRAKES 
 
 FROM what has been said of the brakes in discussing the final 
 drive and the various methods of applying the power to the road 
 wheels, it can readily be understood that there would be little uni- 
 formity as regards brake construction and location, except that 
 all states have laws which specify that vehicles must be equipped 
 with two-brake systems one system for ordinary service and one 
 for emergency. In horse-drawn vehicles, the brakes are applied 
 directly to the steel tires; however, since rubber is quite ex- 
 pensive, this method of brake application is not commercially 
 possible; but it is effectively accomplished by securing to the 
 wheels a metal drum, on which the friction members act. 
 
 Until recently more attention has been given to acceleration 
 of the commercial car than to the retarding forces at the driver's 
 disposal. This subject at present is receiving considerable study, 
 which is evident by the variety of types and the numerous loca- 
 tions. The brakes are invariably applied to the rear wheels, as 
 they present considerable advantage, supporting the greatest por- 
 tion of the vehicle and load. 
 
 On vehicles employing the double side-chain drive, it has been 
 considered good practice to place one set of brakes on the jack- 
 shaft and one set in the rear wheels. There are various positions 
 for this brake, either inside or outside of the frame. This type of 
 brake can be made light and powerful, but possesses other disad- 
 vantages which have led some makers to place both brakes in the 
 rear wheels. On shaft-driven vehicles, one brake can be mounted 
 either at the front or rear end of the propeller shaft and one set 
 in the wheels, or both sets may be placed in the wheel drums. 
 
 Locations. Rear- wheel brakes for either type of final drive 
 may be divided into three general arrangements, viz., two in- 
 ternal brakes on the same drum, one internal and one external 
 brake on the same drum and one external and one internal or two 
 internal brakes operating on concentric drums. 
 
 Types. There are two general types of brakes the band and 
 shoe types, and either may be made external contracting or in- 
 
 172 
 
MOTOR TRUCK BRAKES 
 
 173 
 
 ternal expanding. The band type consists of a continuous steel 
 band having a fabric frictional facing, while the shoe type may 
 either be of cast iron with a high percentage of manganese, of 
 phosphor bronze with cork inserts, or provided with a fabric 
 facing. 
 
 When frictional facings are not used, the shoes are provided 
 with diagonal grooves to prevent chattering and squeaking. 
 Each type presents a variety of constructions, as regards anchor- 
 age, adjustments, and operating mechanism. In addition to the 
 brakes acting on the rear wheels, the Saurer motor brake can also 
 be mentioned. 
 
 The writer, in discussing this subject, will endeavor to cover 
 the principal types in use and in conclusion outline their advan- 
 tages and disadvantages. 
 
 Considering first the chain-driven vehicles, we find two loca- 
 tions for the service brake, either outside or inside of the frame. 
 
 FIG. 149. Knox Jack Shaft Brake. 
 
 Jackshaft Brakes. Fig. 149 serves to illustrate the jackshaft 
 brake used on the Knox tractor. This is of the shoe type mounted 
 outside of the frame and is anchored to the frame side rail by 
 heavy brackets. Like all jackshaft brakes, this is of the high- 
 speed type and equipped with two cast iron brake shoes, which 
 are easily removed for renewal and mounted on large supports, 
 while ample adjustment is provided through the rod connecting 
 the two shoe supports with the operating lever. The brake drum 
 is made from cast steel and is fourteen inches in diameter with 
 four-inch face. It is attached to a hub which also carries the 
 
174 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 driving sprocket. Features worthy of attention in connection 
 with this construction are the particular attention paid to the 
 strength of the brake anchorage and the unusual provision for 
 cooling presented by the twenty ribs on the brake drum. 
 
 Hydraulic Rear-wheels Brakes. The rear-wheel brakes are 
 perhaps the largest ever attempted and are 20 ins. in diameter 
 with a 6^-in. face. They consist of steel shoes lined with friction 
 fabric and hydraulicallly operated. This hydraulic mechanism 
 is of ingenious design, so that there is practically no difference in 
 their operation from the ordinary hand brakes. A pump lever 
 takes the place of the ordinary hand lever and a button for the 
 release of the brake. To apply the brakes, the operator makes 
 two or three full strokes with the handle forward and backward 
 and the application of the brake will then be felt in the form of a 
 resistance pulling the lever backwards, the same as with the hand 
 lever. After the resistance is felt a good hard pull on the handle 
 will lock the rear wheels. The release is accomplished by push- 
 
 FIG. 150. Kelley Internal Expanding- Rear Wheel Brake. 
 
 ing the button on the top of the handle and pushing the handle 
 forward beyond the stop normally interposed. Passing beyond 
 this stop exposes a release part in the pump, which allows the 
 liquid to flow back through the pump into the reservoir. 
 
 Most any of the following brake constructions can be applied 
 to the jackshaft, while they may be placed either outside of the 
 sprocket, between sprocket and frame and as mentioned pre- 
 viously inside of the frame. 
 
MOTOE TKUCK BRAKES 
 
 175 
 
 Rear-wheel Brakes on Chain-drive Models. When both brakes 
 are located in the rear wheels, they are generally of the internal 
 expanding type. The reason for this is, should an external brake 
 become disarranged, the chain and other parts may be injured, 
 due to the brake mechanism being caught in the chain or sprocket. 
 
 The Kelly and Natco trucks are examples of this type. The 
 Kelly brake construction, shown in Fig. 150, presents an excellent 
 arrangement and possesses several features. These brakes are of 
 the shoe type, located side by side, lined with a friction fabric, 
 
 BfiAHf 
 
 FIG. 151. Natco Double Eear Wheel Brake. 
 
 and operated by a combination toggle and eccentric. Each set of 
 shoes are hinged on liberal eyed pins and anchored to the brake 
 spider, which is attached to the radius rod. A toggle action, 
 operated by an eccentric or cam, expands the front end of the 
 shoes, while the tubular shafts, operating the eccentrics, extend 
 through the brake spider flange extensions and are keyed at the 
 outer ends of the worm-wheel operating levers. This feature 
 places the brake adjustment outside of the wheel so that adjust- 
 ment can be obtained without removing the wheels. Another 
 feature is the provision of large grease cups arid liberal grooves 
 for lubricating the various shaft bearings. 
 
 The Nacto Brakes (Fig. 151) are also of the lined-shoe type; 
 however, they differ from the above in that they are cam actuated 
 and have their adjustment incorporated in the brake linkage. 
 Each pair of shoes is hinged to the spider at one end, while the 
 other end carries hardened steel plates, against which the cam 
 
176 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 bears in expanding the shoes. The shoes are not rigidly attached 
 to the hinge pins, but are free to move and, in applying the 
 brake, the forward end engages the drum first, so that this free 
 end permits the shoe to engage more evenly at all points of its 
 circumference. 
 
 Brakes on Shaft-drive Models. The two brake locations in 
 the shaft-drive vehicle are on the propeller shaft and rear wheels, 
 or both in the rear wheels. This applies to either bevel, double 
 reduction, internal gear, or worm drive, the bevel and double re- 
 duction axles universally using the double rear- wheel brake. 
 
 FIG. 152. Fierce-Arrow Propeller Shaft Brake. 
 
 Propeller-shaft Brake. The Fierce-Arrow worm-drive trucks 
 offer an excellent example of the propeller shaft brake. This 
 brake (Fig. 152) is located immediately back of the transmission 
 and anchored to a frame cross member. In this type, two cast- 
 iron shoes are brought to bear against the cast steel brake drum. 
 These shoes are hinged to arms on each side of the drums, these 
 arms in turn are hinged to a bracket, which is attached to the 
 bottom of the cross member, the top ends pivoting on the op- 
 erating shaft. Springs are placed on the operating shaft, between 
 these two arms, to keep the brake released. Mounted on the 
 operating shaft, is a ratchet, which is prevented from turning by 
 a tongue fitting into a groove in one arm. The brake lever has 
 an integral ratchet, which meshes with the ratchet mounted on 
 the operating shaft, forming a means of applying the brake. A 
 nut is placed at the other end of the operating shaft, forming the 
 brake adjustment. The drum has an integral ratchet, and a pawl 
 lever is attached to the lower link, being held erect, out of en- 
 
MOTOK TKUCK BRAKES 
 
 177 
 
 gagement by a spring. This forms a ratchet type of sprag for 
 locking the wheels on steep hills and removes the strain from the 
 brakes. 
 
 The Packard worm drive and G.V. internal gear-drive trucks 
 also employ the transmission brake, while the Mais, Fremont- 
 Mais and 3|-ton Republic internal gear-driven trucks have the 
 service brake mounted on the pinion shaft and anchored to the 
 axle housing. 
 
 FIG. 153. The Sheldon Internal Expanding- Brake. 
 
 Band Brake. The Sheldon brake (Fig. 153) illustrates a 
 simple band brake, sometimes called a single expanding shoe, 
 operated by a toggle linkage. This type of brake is used on this 
 company's worm-drive axles, being located side by side in the 
 rear-wheel drums. The bands are supported by three brackets 
 bolted to the brake spider, which carries the operating levers and 
 shafts. The bands are expanded through small links attached to 
 brackets riveted to them and a long link attached to the lever on 
 the operating shaft. A large stud, located in the spider, prevents 
 them from rotating. A coil spring releases the bands and holds 
 the brackets in contact with the stud. Adjustment is made 
 through the brake linkage and one of the toggle links. 
 13 
 
178 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 Internal and External Brakes. The Clark Equipment Com- 
 pany offer an excellent example of internal and external rear- 
 wheel brake (Fig. 154) in the construction employed on its inter- 
 nal gear-driven axles. The external brake is anchored to one end 
 of the brake spider while the other end is provided with a simple 
 adjustment for taking up the wear of the lining. The internal 
 brake band is also lined with a friction fabric and expanded by 
 a cam. This cam operates on hardened steel plates, set into the 
 
 ADJUSTMENT 
 
 ADJUSTMENT 
 
 FIG. 154. Clark Internal and External Brakes. 
 
 brake band brackets and so arranged that they can easily be re- 
 newed. The forward end of the brake is supported by an exten- 
 sion of the brake spider and has liberal provisions for adjustment. 
 An excellent feature in connection with this brake is the pro- 
 vision of a metal disc and packing separating the gear compart- 
 ment from that of the internal brake. This, in addition to mak- 
 ing it possible to lubricate the gears with graphite, guards against 
 the breakage of the gears in case any part of the brake mechan- 
 ism should come loose. 
 
MOTOK TEUCK BKAKES 
 
 179 
 
 Another good example of internal and external brake con- 
 struction is shown in Fig. 155 and used on the Autocar. The ex- 
 ternal brakes are of the double shoe type, fabric-lined and hinged 
 to a stud projecting from the brake spider, and small clevises, 
 attached to the spider, hold the shoes longitudinally on the drum. 
 They are connected at the front end by a rod, which forms the 
 adjustment and also carries the springs to release the brake. The 
 
 FIG. 155. Autocar Internal and External Brakes. 
 
 internal brakes are also of the shoe type, fabric-lined and hinged 
 to the brake spider. They are expanded by a double-armed lever 
 which is connected to them by links. This lever is similar to a 
 bell crank, with pins extending laterally from the ends of its 
 arms, to which the links are attached. 
 
 Concentric Brakes. The G.M.C. construction, Fig. 156, de- 
 picts a type employing concentric drums. The internal brake is 
 of the conventional shoe type, fabric-lined, expanded by a cam 
 and operating on the inner drum. The external brake operates 
 on the outer drum, being of the band type and contracted by a 
 
180 MOTOE TKUCK DESIGN AND CONSTEUCTION 
 
 double-armed lever. This double-armed lever is formed integral 
 with the operating shaft and is slotted to receive the band bracket 
 and the clevis rod, which carries the releasing spring and also 
 forms the adjustment. 
 
 FIG. 156. G.M.C. Concentric Brakes. 
 
 The Timken Duplex Brake. The Timken Detroit Axle Com- 
 pany has recently introduced a new type of brake (Fig. 157) on 
 its worm-drive axles, which is termed a " duplex brake." These 
 brakes consist of four fabric-lined shoes, located in such a manner 
 that the pair of brakes takes up but little more room than a single 
 brake of ordinary shoe type. These four shoes are equally spaced 
 on the inner circumference of the brake drum and each pair 
 located diametrically opposite are expanded by cams and sup- 
 ported by the brake spider and large pins. One pair of shoes 
 has single arms, which extend to the cam and its support and 
 these pass between two arms of the other pair of shoes. These 
 shoes are made somewhat larger in width, to obtain the proper 
 brake area and are held longitudinally, by means of hardened 
 steel washers on the operating shaft and by the brake spider. 
 
 Any one of the brakes described above, with the exception of 
 the Pierce and Knox, may be applied to a chain- or shaft-driven 
 vehicle in any position mentioned. 
 
MOTOR TRUCK BRAKES 
 
 181 
 
 Saurer Motor Brake. Another type worth mentioning is the 
 Saurer brake, being an air brake worked by the the throttle lever. 
 For a quarter of a circle this lever controls the throttle, but 
 beyond this position, through a device incorporated in the car- 
 buretor, it causes the motor to operate on the two-cycle principle, 
 compressing air in the cylinders to an extent which enables the 
 car to be controlled on a 20 per cent, grade without the need of a 
 brake. 
 
 FIG. 157. Timken Duplex Brake. 
 
 In applying any type of brake, it must be held from rotating 
 and this strain is generally taken by the brake spider which rides 
 free on the axle or jackshaft and transmits this strain to the 
 radius rod or frame on the chain-driven vehicles and to the axle 
 housing on shaft-driven vehicles. 
 
 Mounting the service brake on the jackshaft or propeller shaft 
 places these brakes where they are well protected and, as they 
 are of the high-speed type, the reduction through the chains or 
 gearing makes them more powerful. This presents a disadvan- 
 tage, in throwing the entire braking strain on the chains or drive 
 shaft and differential and thus shortening their lives. Should 
 the chains or drive shaft break on a bad hill, and the emergency 
 
182 MOTOK TRUCK DESIGN AND CONSTRUCTION 
 
 brakes be out of commission, serious damage would result. Al- 
 though this may rarely occur, some makers have protected their 
 vehicles against such accidents, by placing both sets of brakes 
 in the rear wheels, thus placing the retarding force as near as 
 possible to the point where the momentum of the vehicle is 
 checked. In a sense, this argument is true, especially on the 
 heavier vehicles, for the fewer elements there are between the tire 
 and brake, the fewer are subjected to stress and the fewer are the 
 chances of failure. 
 
 Brake adjustments are also receiving considerable study and, 
 while in some cases they are almost hidden, in others they are 
 very accessible. This adjustment may either be incorporated in 
 the brake linkage or in the brake. The tendency seems to be 
 toward locating it in the brake in such a manner that it is ac- 
 cessible without removing the wheel. 
 
 Brake equalizers are quite common on commercial cars, the 
 well-known whippletree type being quite popular. 
 
 When a single brake is applied on the propeller shaft, the 
 differential takes care of the distribution of force to the two 
 wheels equally, but this kind of compensation has a disadvantage, 
 in that, if the adhesion of the two wheels is greatly different, that 
 with the slightest grip on the road may actually cause it to rotate 
 backwards. Still, it is only on very rare occasions that this re- 
 verse motion occurs and it is not, therefore, a cause of much 
 added tire wear. 
 
 If the braking forces are not equalized, the task of adjusting 
 the brakes is much more difficult than it need be. On one vehicle, 
 the whippletree equalizer is replaced by a diminutive differential 
 gear, providing a smoother action and a much larger range of 
 equalization. 
 
CHAPTEE XIII 
 
 THE FEONT AXLE 
 
 THE front axle with its steering gear, knuckle and arms is 
 largely depended upon for the safe control of the vehicle, while 
 it must also carry the forward portion of the vehicle and load. 
 It must be so arranged as to permit steering the car and in order 
 to accomplish this, the front wheel spindles are pivoted in the 
 axle end and are held in proper relation to each other by a tie 
 rod, which connects levers extending from each pivot. Another 
 lever extends from either right or left-hand pivot (depending 
 upon left or right-side drive) which is connected by a drag link 
 with the steering gear. 
 
 This pivot is termed the steering knuckle and has the wheel 
 spindle formed integral, while the levers may either be formed 
 integral, or attached to the knuckle. 
 
 Three General Types. There are three general types of steer- 
 ing knuckles, known as the Elliot, Reversed Elliot and Lemoine 
 types. In American practice the Elliot type is most extensively 
 used and the Lemoine least. In the Elliot type the ends of the 
 axle proper are forked and the steering knuckle is T-shaped, 
 while in the reversed Elliot the knuckle is forked and the axle 
 end forms a T. In the Lemoine type both axle end and knuckle 
 form L's. In practice each of these types differ somewhat, de- 
 pending upon the type of bearings and the method of mounting 
 the knuckle in the axle end. 
 
 For some time it was the general impression that when the 
 plane of the front wheel was in line with the plane of the knuckle 
 pivot, the effect of road inequalities would not be transmitted to 
 the steering gear. This contention led to the introduction of a 
 type of knuckle in which the wheel center lies very close to the 
 pivot center. 
 
 The knuckle in this type, instead of having a T-shape, in- 
 cludes a sort of a yoke extending outside of the wheel hub to 
 points close to the spokes and the forked axle ends are pivoted to 
 the yokes at these points. However, this is of minor importance, 
 since the speed of commercial cars is comparatively low and with 
 a semi-reversible gear the road shocks are not transmitted to the 
 
 183 
 
184 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 steering wheel. One prominent maker employed this type of 
 knuckle for a number of years, but has discarded it and is now 
 using the Elliot type. 
 
 The levers to which are attached the tie rod used for connect- 
 ing the two knuckles and the one for connection with the steering 
 gear are known as knuckle arms. These may either be formed 
 integral with the knuckles, or attached by means of a taper and 
 keyway, retained by a castellated nut. One prominent maker 
 forms the spindle and levers separately so that they may be dove- 
 tailed together and retained by the pivot pin. The general prac- 
 tice is to attach them to the knuckles since this simplifies manu- 
 facturing and replacement. 
 
 Owing to their importance, the knuckles and arms are always 
 forged from a good quality of steel and heat treated. The tie rod 
 may either be placed in front or in the rear of the axle, while the 
 steering connection may either be arranged for cross or fore and 
 aft steering. The arrangement of tie rod and steering connections 
 depend upon the general construction of the vehicle and the loca- 
 tion of the steering gear. 
 
 The Axle Proper. The axle proper may either be forged from 
 medium ca,rbon steel of solid rectangular section or of I-beam 
 section, approaching a full rectangular section. Cast steel axles 
 are also used, while one maker of a popular priced vehicle uses 
 cast steel ends with a round section center. These axles may also 
 be built up with tubular centers, flat plates riveted together, or 
 from pressed steel of channel section. 
 
 Attachment to Frame. In conventional designs the only con- 
 nection between the axle and the frame is through the front 
 springs, which with few exceptions are of the semi-elliptic type. 
 One maker uses a full elliptic front spring and provides a dis- 
 tance rod to hold the axle in alignment with the frame. 
 
 Fig. 158 illustrates a front axle with cast steel center for light 
 delivery cars of 750 to 1,000 Ibs. capacity. The center is dropped 
 considerably, that is, the topmost surface of the axle bed is located 
 considerably below the center of the wheel spindle, since it is in- 
 tended for use with full elliptic front springs and pneumatic 
 tires. The knuckle is of the Elliot type and drop -forged with 
 integral spindle and has a boss at its lower end which is provided 
 with taper and keyway for attaching the knuckle arm. The tie 
 rod is placed to the rear of the axle center and is attached to the 
 knuckle arms by a clevis and bolt. The knuckles are arranged for 
 
THE FEONT AXLE 
 
 185 
 
 cross steering and one clevis bolt has an extension which carries a 
 cross to which the drag link is attached. This cross serves as a 
 universal coupling to compensate for the angular positions of the 
 
 CUP f CON 
 BALL BEARING 
 
 FIG. 158. Light Truck Axle with Cast Center. 
 
 knuckle arms and the variation in the vertical movement between 
 axle and frame. This is necessary as the steering gear is always 
 
 FIG. 159. Vulcan 5-Ton Front Axle. 
 
 attached to the frame and the action of the springs tend to vary 
 the distance between the frame and the axle. The hubs are mal- 
 leable castings with flanges, which hold the spokes of the wheel. 
 
186 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 Cup and cone ball bearings are used for mounting the hubs on 
 the spindle. Bearing adjustment is by means of a nut on the 
 spindle and spacing washers. 
 
 The Vulcan Front Axle. The Vulcan five-ton axle (shown in 
 Fig. 159) offers an example of heavy vehicle construction ar- 
 ranged for fore and aft steering, with the tie rod located to the 
 rear of the axle. 
 
 The axle center is a drop forging with integral spring seats. 
 These spring seats are placed as close as possible to the wheel 
 center in order to obtain the maximum capacity. The stress, due 
 to both the combined weight of the vehicle and its load and that 
 due to the wheel striking an obstruction, increases from nothing 
 at the center of the wheel to a maximum at the center of the 
 spring seat. For this reason a minimum distance is desired. It 
 is customary to increase the section of the axle center between the 
 knuckles and spring seat centers, both in a vertical and horizontal 
 plane to withstand this stress. The knuckles on this axle are also 
 of the Elliot type, but instead of forging the spindle integral with 
 the knuckle pivot and keying the arms to the former, these parts 
 
 are forged separately and 
 keyed together by integral 
 keys. The pivot pin has 
 a shoulder at one end and a 
 nut at the other end to 
 hold them together and the 
 entire unit is supported 
 by bushings and thrust 
 washers in the fork of the 
 axle center. The hub con- 
 struction is of conventional 
 design, employing annular 
 ball bearings for wheel 
 mounting. 
 
 The Peerless Axle. 
 
 Fig. 160 depicts the Peer- 
 less front axle, which is 
 built along conventional 
 lines with drop forged cen- 
 ter, integral spring seats and Elliot type knuckles. In detail, this 
 construction differs from those mentioned above in that the bush- 
 ings for supporting the pivot pin are located in the knuckle in- 
 
 FIG. 160. Peerless Front Axle. 
 
THE FKONT AXLE 
 
 187 
 
 stead of in the axle fork. Thrust washers are replaced by a ball- 
 thrust bearing, located in the upper part of the fork. The steer- 
 ing arm is forged integral with the knuckle arm and attached to 
 the knuckle by a taper and key. The steering arm being so ar- 
 ranged as to clear the lower surface of the center. The front 
 wheels are mounted upon 
 Timken roller bearings and 
 dished, that is, the wheel 
 spokes are set at angles 
 with a plane perpendicular 
 to the axis of the wheel. 
 
 The Timken Front Axle 
 (Fig. 161) is used on a num- 
 ber of commercial cars. It 
 has a drop forged center of 
 I-beam section, and Elliot 
 knuckles. The axles are 
 arranged for either type of 
 steering to meet the re- 
 quirements of vehicle mak- 
 ers. However, in this case 
 the cross steering arrange- 
 ment with the tie rod and 
 drag link located in front 
 of the axle is shown. The 
 
 knuckle and pivot pin are locked together with a bolt, so that this 
 part is properly supported by the Timken bearing in the axle 
 fork. Timken bearings are also used for wheel mounting. 
 
 The axles mentioned above are all arranged for right-side 
 steering, while the Natco axle (Fig. 162) arranged for left-side 
 fore and aft steering with the tie rod located at the rear of the 
 axle. It is of conventional design with Elliot knuckles and pivot 
 pin bushings located in the knuckles. This illustration shows 
 how the center is dropped to provide the proper clearance between 
 it and the radiator or other units which may be near it. It also 
 shows the method of providing clearance for the tie rod and it 
 will be noted that this is not bent to the shape of the axle, as pro- 
 vision must be made to compensate for the movement of the 
 knuckle arms. This axle is an example of light truck construc- 
 
 FIG. 161. 
 
 Plan and Side View of Tim- 
 ken Front Axle. 
 
188 MOTOR TEUCK DESIGN AND CONSTRUCTION 
 
 tion, and also presents one method of driving the speedometer by 
 gearing from the wheel. 
 
 STEEPING 
 MOTION 
 OF 
 
 
 FIG. 162. Natco Axle Top and Side Views. 
 
 Pierce Axle. The Pierce worm-driven trucks are equipped 
 with front axles having reversed Elliot type knuckles and fore 
 and aft right-hand steering. The axle center is an I-beam section 
 
 5TEER/NG ARM 
 
 FIG. 163. Type of Front Axle used on Pierce- Arrow Worm-Driven Trucks. 
 
 forging and is perfectly straight, with integral spring seats. The 
 pivot pin bushings are located in the knuckles and so arranged 
 that the thrust is taken by the shoulders of these bushings and a 
 
THE FRONT AXLE 
 
 189 
 
 J 
 
 FIG. 164. Packard Front Axle. 
 
 thrust washer. The pivot pin has a taper which fits into the axle 
 center so that it can be drawn up tight by a castellated nut. The 
 wheels are mounted on 
 Timken roller bearings as 
 shown in Fig. 163. 
 
 Packard Axles. The 
 new Packard worm-driven 
 trucks are equipped with 
 front axles (Fig. 164), em- 
 ploying the reversed El- 
 liot type of knuckle; how- 
 ever, they are arranged for 
 left side fore and aft steer- 
 ing. The axle proper, how- 
 ever, is dropped at the center. This construction is similar to the 
 one depicted above, with the exception of the steering arms, which 
 are attached to the lower part of the knuckle. This permits 
 proper clearance for the tie rod and places it in such position that 
 it is not necessary to bend it. A feature worthy of attention on 
 both of these axles is the provision of ball and socket connections 
 for the tie rod and drag link in place of the more customary clevis 
 
 and bolt. These ball and 
 socket joints have springs 
 so that the wear in the 
 steering connections is auto- 
 matically taken up. 
 
 The International Har- 
 vester Corporation trucks 
 for some years had used the 
 Sarven type of wheel in 
 connection with an Elliot 
 type of steering knuckle, in 
 which the pivot center lies 
 very close to the center of 
 the wheel. This is shown 
 in Fig. 165 and it will be 
 noted that the hub construc- 
 tion resembles an ordinary 
 vehicle wheel hub. This 
 consists of wooden hubs 
 
 with steel hub flanges, the former have steel shells which carry the 
 wheel bearings. The outer wheel bearing is of the roller type 
 
 FIG. 165. Axle used on some of the In- 
 ternational Harvester Trucks. 
 
190 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 made by the I.H.C., while the inner bearing consists of a steel and 
 bronze shell, the latter having a taper bearing in the shell in- 
 serted in the wood hub. The bronze shell is provided with oil 
 holes and grooves, so that the entire bearing can work in graphite 
 and grease. The knuckle, instead of having the usual hub for the 
 pivot pin or king bolt, as it is sometimes called, has a yoke, which 
 fits into the axle yoke. Short pins pass through the axle and 
 knuckle yokes to form the pivot. 
 
 The above axles all have drop forged centers, which may 
 either be forged in one piece or the two ends may be forged sep- 
 arately and welded together at the center. 
 
 The Reo Axle. The Reo two-ton front axle (Fig. 166) differs 
 from those shown above in that the center is built up from a bar 
 of round section, pinned and brazed into cast steel ends which 
 form the forks. The knuckles are of the Elliot type and carry 
 the bushings for the pivot pin. The knuckle arms fit over the 
 
 FIG. 166. Reo 2-Ton Front Axle. 
 
 ends of the knuckle and are held in unison with knuckle by two 
 keys. This axle is arranged for left-side steering and the tie is 
 placed directly back of the axle bed. It is not necessary to bend 
 it, since ample clearance is obtained by placing the spring seats 
 above the wheel center. The wheels are mounted on Timken 
 roller bearings and retained by a castellated nut and keyed 
 washer. 
 
 Vim and Commerce Axles. The Vim and Commerce trucks 
 also employ built-up axles with Elliot knuckles, but the center 
 or bed is made of tubular section. The Avery farm trucks em- 
 ploy another type of built-up front axles. A malleable casting 
 forms the steering head to receive the Lemoine type of knuckle, 
 which is equipped with a series of hardened steel washers to take 
 the thrust. 
 
THE FKONT AXLE 
 
 191 
 
 FIG. 167. Lemoine Type of Knuckle. 
 
 On either side of the steering head extensions are riveted a 
 couple of steel plates as shown in Fig. 167. These are straight at 
 the spring seats and bent up slightly at the ends to attach to the 
 steering head castings. 
 Blocks are placed between 
 the two axle plates di- 
 rectly under each spring 
 to form the seat. The 
 steering connections are 
 arranged for cross steer- 
 ing and are located in 
 front of the axle. 
 
 The three-wheel "Wayne 
 Light " commercial car 
 having a capacity of 800 
 Ibs. also employs a built- 
 up front axle as shown in Fig. 168. Two sections of rolled chan- 
 nel steel are riveted together and with drop forged yokes and 
 Elliot type knuckles at either end. 
 
 Pressed steel centers may also be used, while combinations of 
 the above types may also be worked out. 
 
 Bearings. All American trucks are equipped with anti-fric- 
 tion bearings such as the ball and roller types, which are capable 
 of carrying both a radial and thrust load. The mounting of 
 
 these bearings presents no 
 difficulty and they are usu- 
 ally provided with adjust- 
 ments to compensate for 
 wear. The tie rods and 
 
 FIG. 168. Wayne Light Axle, Bnilt-Up dra g links . a1 * 6 made f 
 Type. tubular section and are pro- 
 
 vided with adjustments so 
 
 that the alignment of the wheels may be properly maintained. 
 Lately there seems to be a tendency to use the ball and socket 
 joint for these in preference to the clevis. The former will to a 
 considerable extent take up the wear automatically and can also 
 be more efficiently lubricated. 
 
CHAPTEE XIV 
 
 STEERING GEARS AND FUNDAMENTAL PRINCIPLES OF STEERING 
 
 MECHANISMS 
 
 Certain Principles That Must be Understood in Designing 
 Them. Some interesting problems pertaining to the design, con- 
 struction and operation of the modern commercial car are found 
 in the various steering mechanisms employed. Like almost every 
 other important mechanical features, the steering devices now in 
 general use have resulted from a careful study of the conditions 
 to be fulfilled, supplemented by extensive experiments with dif- 
 ferent types. These researches have resulted in a general steering 
 system which is applied in different forms to all standard com- 
 mercial vehicles. This, in brief, consists of a hand-wheel, con- 
 nected through some form of linkage and gearing leverage to 
 the front wheels of the vehicle, these wheels being carried on 
 pivoted ends of the front axle. The design and construction of 
 some of the most important features of this general arrangement 
 afford interesting subjects for discussion. 
 
 Throw of Front Wheels. Commercial vehicles must neces- 
 sarily be operated within a limited space such as a narrow street, 
 and it is of importance that the extreme throw, from side to side 
 of the front wheels be settled upon, as the amount of this throw, 
 together with the wheelbase and tread determines the turning 
 radius. In practice the latter two items are established by the 
 load or body requirements, and with these fixed, the throw of the 
 front wheels is usually limited by the width of the body, frame 
 or springs and the permissible distance between the pivot cen- 
 ters about which the wheels swing. The angles which the con- 
 necting linkage make, become too acute or obtuse according to 
 their location, if the maximum throw of the wheels is made more 
 than 35 degrees. If this throw is exceeded, steerage is difficult 
 and unsafe. 
 
 The theoretical center about which the vehicle turns is some- 
 what in the center line of the rear axle prolonged, the exact loca- 
 tion being determined by the intersection of this line by a line 
 drawn normal to the inside front wheel. Another line drawn 
 from this intersection to the center of the outside front wheel 
 
 192 
 
STEEEING GEARS 
 
 193 
 
 should be normal to this wheel if it is at the correct angle to pre- 
 vent excessive side slip, which is very destructive to the vehicle 
 
 tire. The four wheels will describe concentric circles about this 
 theoretical center. This is clearly illustrated in Fig. 169 and it 
 will be noticed that the minimum turning radius is the radius of 
 14 
 
194 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 the arc described by the outer front wheel when these wheels are 
 in the position of maximum throw. The differential device allows 
 the proper relation of speed between the rear wheels. 
 
 The outer front wheel pivot is turned a smaller angle than 
 the inner, and they are connected, by a cross rod, rigidly attached 
 to them. There must be some compensating device interposed to 
 give the same angular relation when the wheels are turned in the 
 opposite direction. This is accomplished by making use of the 
 principle of varying ratios of sines of the angles at different 
 
 FIG. 170. Arrangement of Knuckle Levers and Tie Eod for Front and 
 
 Rear Positions. 
 
 points in the arcs through which the knuckle levers turn. This 
 necessitates locating the pivot or knuckle levers so that their cen- 
 ters diverge if they project ahead of the axle, and converge if 
 they project back of it. As the wheels swing, the knuckle lever 
 mounted on the spindle of the inner wheel travels away from the 
 dead center arc, thus traveling a smaller angular distance. This 
 is illustrated by heavy lines, Fig. 170, which are shown for both 
 front and rear location of the cross-rod. 
 
 Knuckle Lever Angles. There are various methods of theo- 
 retically determining the proper angles of these levers, either 
 mathematically or graphically; however, this is largely a matter 
 of compromise, between what is theoretically correct and what is 
 attainable practically. Some makers follow the practice of lay- 
 ing out these steering connections so that the center line of the 
 knuckle lever extended will intersect the center of the rear axle. 
 Others endeavor to obtain a knuckle lever length and angle, that 
 while fitting into the general layout of the vehicle, gives the 
 
STEEEING GEARS 195 
 
 largest possible range of steering angle without undue error. 
 This is generally determined more by experience than by any 
 figures. Another point which must be considered in the general 
 layout, is the various lengths of wheel bases and this suggests 
 making the angle of the knuckle levers as small as possible, con- 
 sistent with reasonable clearance between the ends of the cross 
 tube and the spokes of the wheels. 
 
 Location of Knuckle Levers. Both front and rear positions 
 of these two levers are used and each position possesses its ad- 
 vantages and disadvantages. Some makers prefer the forward 
 location for the reason that it enables large steering angles to be 
 used safely, thus diminishing the turning radius of the vehicle. 
 With the rear position the tie-rod, connecting these two levers, is 
 better protected from injury, providing the proper clearance can 
 be obtained under the engine base. The length of this tie-rod is 
 so adjusted that with the front wheels in the central position the 
 distance apart of the w T heel felloes at the height of the spindle is 
 from 3/16 in. to 5/8 in. less in front of the axle than back of it. 
 The amount of toe-in depends upon the diameter of the wheel, 
 the lower figures being used for wheels 34 ins. or less. This 
 toeing-in is intended to allow for slight play in the joints of the 
 tie-rod and the flexure of its members. It is also intended to cor- 
 rect the tendency of the wheels to toe outward when the vehicle 
 is moving. 
 
 Inclination of the Wheel Spindles. The spindle upon which 
 the wheel revolves is generally inclined from 1^ to 2 degrees 
 below the horizontal center, while the king bolt about which the 
 wheel pivots is brought as close to the spokes as possible, in order 
 to bring the point of intersection of the center of the wheel with 
 the ground as close to the center of the bolt produced as possible. 
 This distance forms the lever arm at the end of which the re- 
 sistance to motion of the front wheels acts when the wheels swing 
 around for steering. 
 
 To approximate castor steering, some manufacturers also in- 
 cline the axles and king bolt in a fore and aft plane, as in Fig. 
 171, the inclination being about four degrees on the average. The 
 reasons for these features are that they make steering easier, in 
 that the construction produces a trailer effect which tends to ob- 
 viate serious consequences in the event of breakage or disconnec- 
 tion of the steering linkage. The point of wheel contact with the 
 ground is behind the point at which the center of the king bolt 
 
196 MOTOK TEUCK DESIGN AND CONSTRUCTION 
 
 FIG. 171. Trailer Effect when Cas- 
 tor Steering is Approximated by In- 
 cluding King Bolt. 
 
 produced meets the ground, hence the steering wheels trail and 
 are automatically kept in the straight ahead position by the road 
 
 resistance. This trailer ef- 
 fect somewhat reduces wob- 
 bling of the front wheels and 
 also reduces the shock on the 
 steering gear. 
 
 Reversibility of Steering 
 Gears. To prevent road 
 shocks from being trans- 
 mitted to the operator's 
 arms, it is considered best to 
 have the steering gear back- 
 locking, or irreversible to 
 some extent at least. With 
 a perfectly reversible system 
 it is evident road shocks, 
 which are transmitted to the 
 operator's hands, depend 
 on their magnitude and the lever arm through which they act. 
 This system is best adapted to show moving vehicles running 
 over smooth pavements, such as the light electric vehicles in 
 common use. 
 
 Between the limits of reversible and irreversible steering 
 gears, is the semi-reversible type, which allows the vehicle wheels 
 to be turned independently of any effort exerted on the steering 
 wheel, yet exerting an even resistance to movement. This feature 
 allows the road wheels to follow the path of least resistance and 
 at the same time indicates to the operator the extent and direc- 
 tion of the movement by more or less swerving of the steering 
 wheel depending upon the gear ratio. The semi-reversible sys- 
 tem also relieves the parts of considerable strain which would be 
 present if the vehicle wheels w r ere rigidly held to their position. 
 A disadvantage of the semi-reversible feature is in steering 
 through sandy or muddy roads and in crossing obstructions such 
 as car tracks obliquely. 
 
 Irreversible Gear for Heavy Service, Heavy service seems to 
 offer a logical field for the irreversible gear as the connection 
 may be made heavy and strong. Considerable manipulation of 
 the steering wheel is usually necessary on these vehicles, which 
 tends to make this type a favorite by relieving the operator of 
 
STEEEING GEARS 197 
 
 jerks and considerable muscular exertion on the steering wheel. 
 It also permits a very low gear ratio or large hand wheel motion 
 which is quite desirable from the leverage standpoint in operating 
 a heavy vehicle when at a standstill or moving very slowly. 
 
 Steering-gear Ratios. Because a commercial vehicle is heavier 
 and slower than a pleasure car, it necessarily has a different kind 
 of steering gear. Theoretically the layout would be the same for 
 both machines, if they had the same wheelbase, but practically it 
 is necessary to have a greater reduction in the commercial vehicle 
 because it is heavier and naturally takes a greater leverage to 
 turn the wheels; and also, since this vehicle acts at a slower rate 
 of speed, the reduction can again be greater because it is not so 
 necessary to be able to turn the wheels from one side to another 
 quickly. 
 
 Owing to the great inertia of a moving loaded commercial 
 vehicle, it is not desirable to make quick turns with the front 
 wheels on account of the tremendous stresses involved by the in- 
 ertia force and the high center of gravity. 
 
 The term, irreversible, in itself, is confusing because it has 
 no exact meaning when applied to a steering gear, beyond the 
 rather indefinite condition, that it means that any ordinary road 
 wheel impact will be insufficient to turn the steering wheel. It is 
 simply a question of reduction between the worm and gear or 
 screw and nut, whichever system is used. The greater the reduc- 
 tion the less reversible the system and likewise the slower the 
 motion of the road wheels in relation to the movement of the 
 steering wheel. Hence, the steering mechanism for a heavy 
 vehicle will be less reversible than the steering mechanism for a 
 lighter vehicle. 
 
 Tie Rod. The tie rod connects the steering knuckle levers on 
 opposite sides and is usually of tubular section. When placed in 
 front of the axle it ordinarily works under tension, while behind 
 the axle it works under compression. In the forward position 
 the road resistance encountered by the front wheels, acting 
 through the steering knuckles and arms, puts a tension on the rod 
 and in the rear position a compression. The force impressed by 
 the operator in steering the vehicle produces a tension for one 
 direction of motion and a compression for the other, with both 
 constructions. 
 
 The ends of the knuckle levers swing in the same plane and 
 the tie rod must be connected with forked connectors. These 
 
198 MOTOK TEUCK DESIGN AND CONSTRUCTION 
 
 connectors are generally made adjustable, so that the wheels may 
 be kept properly lined up even if the rod or steering levers be- 
 come slightly bent. The adjustable connectors must be securely 
 clamped and safeguarded against working loose. 
 
 The Drag Link. The drag link may be placed either in a fore- 
 and-aft position or crosswise of the vehicle. The fore-and-aft 
 position is more generally used when the engine is under a hood, 
 while with the seat over the engine it is difficult to place the gear 
 in such a position as to permit placing the drag link parallel with 
 the frame. The gear usually is so close to the front axle that the 
 drag link must be placed crosswise. 
 
 Cushion springs are usually put in the joints of this member 
 to assist in absorbing abrupt shocks which might be transmitted 
 in either direction. These members sometimes are made adjust- 
 able for length, while ad- 
 justments are also provided 
 to take up the tension on 
 the springs. 
 
 An important point in 
 the steering gear layout is a 
 desirability of a proper ge- 
 ometrical layout for the 
 drag link to avoid front 
 wheel Avobble under front 
 spring deflection when the 
 vehicle is in motion. In 
 other words, it is very im- 
 portant to have the drag 
 ^ , . , link so arranged as to 
 
 FIG. 172. Steering- Gear Back of Axle 
 
 and Drag Link Parallel with Frame, produce the least tendency 
 
 to rotate the steering gear 
 
 arm as a result of the action of the front springs. When 
 this member is placed crosswise it should be in nearly the 
 same plane as the tie rod under normal load, but with the fore- 
 and-aft position conditions are entirely different. With this 
 arrangement the drag link may be either forward of or behind 
 the front axle. In the latter position, which is the more popular, 
 this link should be so placed that when the truck is loaded, a 
 straight line drawn through the eye of the front spring will ap- 
 proximately intersect both front and rear ball- joint centers of 
 the drag link, as in Fig. 172. A slight deviation from this inter- 
 
STEERING GEARS 
 
 199 
 
 section will not materially affect the results, depending upon the 
 characteristics of the front spring, but the centers must fall ap- 
 proximately on this line to obtain the proper front wheel action 
 under spring deflections, particularly when such spring deflection 
 is at all excessive. To give as nearly as possible true steering 
 under extreme conditions, it is well to make the front spring as 
 flat as possible, to prevent 
 any great extent of forward 
 or backward movement of 
 the axle. 
 
 On the Mack model "A.C." 
 trucks (Fig. 173) the steer- 
 ing gear and drag link are 
 ahead of the front axle. This 
 member is slightly out of 
 parallel with the frame, when 
 the mechanism is in midpo- FIQ 
 sition, but swings into posi- 
 tion more nearly parallel 
 
 when the road wheels are turned. The front axle, in its move- 
 ments, due to road inequalities, swings through an approximate 
 arc about a point P. The ball on the steering knuckle-arm is as 
 close to this point as conditions permit. The drag link, extending 
 backward, swings about a center Z. Thus, both the axle itself 
 and the ball on the steering knuckle-arm swing through approxi- 
 
 Mack Model "AC" 
 Gear Arrangement. 
 
 Steering 
 
 FIG. 174. Manly Front Spring Mounting. 
 
 mately concentric arcs and no backward or forward motion is 
 imparted to the steering gear arm due to spring deflection. 
 
200 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 On the Manly trucks a similar arrangement is used ; however, 
 this is just the reverse to that of the Mack trucks, in that, the 
 front end of the spring is shackled and the rear end rigidly at- 
 tached to the frame. By this method the end of the drag link, 
 which is pivoted on the steering gear arm, is brought very nearly 
 in line with the pivoted end of the spring so that the axle and the 
 forward end of the drag link connected with the axle is allowed 
 to travel in practically the same curved path. 
 
 The Steering Gear. Horse-drawn vehicles are ordinarily 
 steered by means of a fifth-wheel attached to the forward unit of 
 the vehicle gear, which pivots on what is known as the king bolt. 
 However, the divided axle is universally employed on commer- 
 cial cars. This was described in the preceding chapter on " Front 
 Axles," and the arrangement of pivoting the wheels is known in 
 the country as the Ackerman Steering Gear. 
 
 Technically, this has been revised and at present it is based 
 upon the principle that if the vehicle is to turn a corner without 
 lateral slip of any of the wheels, the steering linkage must be so 
 arranged that the axles of all wheels produced always intersect 
 a common vertical line, this vertical line forming a momentary 
 axis of rotation. This accounts for the use of inclined knuckle 
 arms instead of parallel arms. When they extend toward the 
 rear they must incline toward each other and away from each 
 other when they extend forward of the axle. The inclination is 
 such that the center lines of the arms produced meet at the point 
 near the center of the rear axle. 
 
 Wheel and Mast. Commercial cars are steered by means of 
 hand wheels located at the upper end of the steering column. 
 The spider of the steering wheels is secured to a shaft which gen- 
 erally passes down through an outer tube, usually called the 
 mast. This shaft enters a housing at the lower end, which car- 
 ries the steering mechanism that may either consist of a rack and 
 pinion bevel pinion and bevel sector, worm and sector, worm 
 and wheel, or screw and nut. 
 
 The steering column is generally styled according to the type 
 of steering mechanism employed. One member of the mechan- 
 ism has a shaft extending through the housing and carries the 
 steering lever which is connected by means of a drag link to the 
 steering arm on the front axle. Generally the steering motion is 
 geared down so that one and one-half turns of the hand wheel 
 will give the steering ball arm a motion of about 60 degrees, while 
 
STEERING GEARS 
 
 201 
 
 the lever proportions are such as to give the wheels the maximum 
 angle in either direction. 
 
 For commercial cars, especially those designed for heavy 
 service, it is considered best to have the steering gear back- 
 
 MAST 
 
 STEERING SHAFT 
 FLOOR BRACKET 
 
 HOUSING 
 
 PINION 
 
 PINION 
 
 RACK- 
 
 FIG. 175. Eack and Pinion Type of Steering Gear. 
 
 locking or irreversible, that is, so designed that any shocks re- 
 ceived by the road wheels will not be transmitted to the operator's 
 arms. The lighter vehicles permit the use of a slightly reversible 
 mechanism, in which part of the shock is transmitted to the op- 
 erator's arms, thus reducing the shocks transmitted to the steer- 
 ing mechanism. 
 
 Drag Links and Tie Rods. Drag links are usually of the same 
 proportions as the tie rod of the axle and the general practice is 
 to provide cushion springs to absorb some of the shock which is 
 transmitted to the steering mechanism. There are various con- 
 structions of either the steering mechanism or drag link in use at 
 
202 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 of completeness, it will be necessary to present some illustra- 
 tions, if clearness is to be a property of the text. 
 
 Rack and Pinion Type. The rack and pinion type of steering 
 gear (Fig. 175) is perhaps the simplest type. It consists of a 
 hollow steering shaft which carries the hand wheel at its upper 
 end and a spur pinion within a housing at its lower end. This 
 pinion meshes with a spur rack the end of which extends through 
 
 FIG. 176. Reo Bevel-Type Gear. 
 
 the housing and carries a ball to which the drag link is attached. 
 The column has an outer tube or mast which carries a bearing 
 for the steering shaft. 
 
 This type of steering mechanism is only used for cross steer- 
 ing and is completely reversible, so that the road shocks are trans- 
 mitted to the operator's arms. It is practically limited to use on 
 cars of 1,000-lb. capacity and under, and where the steering pivots 
 can be so arranged that only part of the motion of the road wheel 
 can be transmitted to the steering mechanism. It also possesses a 
 
STEERING GEARS 
 
 203 
 
 disadvantage in that all the load is carried on one tooth, as the 
 space in the chassis frame is not large enough to permit the pro- 
 portions needed to have two or more teeth in mesh. 
 
 Bevel-pinion Type (Fig. 176) illustrates the bevel-pinion and 
 sector type of steering used on the Reo 2-ton chassis. In this 
 construction the steering shaft is made of solid section, which 
 permits securely keying the hand wheel and bevel pinion to it. 
 This, of course, is made possible by placing the spark and throttle 
 control outside of the steering column and locating the levers 
 below the hand wheel. 
 
 The bevel pinion meshes with a bevel gear sector which is 
 attached to a horizontal shaft carrying the steering ball lever. 
 The steering motion is limited by leaving a portion of the sector 
 without teeth, while the thrust of the sector is taken on a steel 
 roller, a spring being used to maintain the roller in contact with 
 the sector. A large bracket forms the frame attachment and also 
 
 TRUNNION BLQCK 
 
 HU1 
 
 STEER/ NG LEVER 
 
 FIG. 177. Steering 1 Gear of the Fierce-Arrow 5-Ton Truck. 
 
 carries the bearings for the horizontal shaft, the thrust roller and 
 supports the lower end of the mast. 
 
 The spark and throttle controls, instead of having the usual 
 sector near the hand wheel, are controlled by means of friction 
 members and springs, located below the foot board bracket, while 
 the accelerator pedal is also mounted on this bracket. 
 
 Bevel gear steering mechanisms have less need for housings 
 than other types, although in some cases they are enclosed. This 
 type of gear is also completely reversible. 
 
 Worm and Sector Type (Fig. 180) depicts the worm and sector 
 type of steering used on the Vulcan 5-ton chassis. It has ball- 
 thrust bearings and a hollow shaft, however, but one control, 
 that of the throttle is built in the column, the spark being con- 
 
204 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 SPARK CONTROL 
 
 HAND WHEEL 
 
 'HRQTTLE CONTROL. 
 
 trolled by mechanism mounted on the dash. The lower end of 
 the steering shaft having an integral worm. This worm meshes 
 with a worm-gear sector mounted on a horizontal shaft and sup- 
 ported by bushings located in the horizontal divided case. 
 
 The customary position for the steering ball lever in the worm 
 type of steering gears, is on the horizontal shaft; however, this 
 position generally limits the motion of the front wheels on the 
 side on which the steering gear is located, as the road wheel will 
 come in contact with the drag link before it can touch any other 
 part. With fore and aft steering the usual method of overcom- 
 ing this is by placing the steering arm of the axle below the axle 
 center and mounting the steering gear in such a manner as to per- 
 mit the drag link to 
 clear inside the front 
 spring. However, this 
 places the steering link- 
 age in a position where 
 it is practically the low- 
 est point of the vehicle 
 and very apt to become 
 damaged by striking ob- 
 stacles in the road. In 
 heavy vehicles consider- 
 able clearance is usually 
 allowed between the front 
 spring and the frame, 
 and in the Vulcan 5-ton 
 truck this clearance is 
 taken advantage of to 
 protect the steering link- 
 age, by passing the steer- 
 ing arm of the axle 
 through this space so that 
 the drag link comes in- 
 side the frame. However, owing to the limited amount of space 
 between the engine and the frame, the steering ball lever can- 
 not be mounted on the horizontal shaft outside of the housing. 
 In order to overcome this, the worm sector of the steering gear 
 has a boss which extends through case and carries the lever. In 
 this way the lever is placed in approximately the center of the 
 column and has ample space for its full movement. 
 
 BALL THRUST 
 SEARING 
 
 'ADJUSTING NUT 
 
 STEERING LEV EH 
 
 FIG. 178. 
 
 Peerless Steering- Gear, 
 and Wheel Type. 
 
 Worm 
 
STEERING GEARS 
 
 205 
 
 Worm and Wheel Type. The Peerless steering gear (Fig. 
 178) differs somewhat from those shown above, being of the worm 
 and wheel type with friction controls mounted above the hand 
 wheel. This hand wheel is attached to the steering shaft by 
 means of a taper and key, while the former is made large enough 
 to form both the shaft and the mast. 
 
 With inside controls and a mast, there is considerable dif- 
 ficulty in providing a shaft of proper proportions, so that in 
 eliminating the mast, the shaft can be made ample in size. Al- 
 though it is somewhat more difficult to provide a bracket on the 
 foot boards, owing to the shaft turning with the hand wheel. 
 
 In this construction 
 a complete worm wheel 
 is used instead of a 
 sector, and as only 
 about 90 degrees of 
 the worm wheel comes 
 in contact with the 
 worm teeth, while the 
 wheels are moved their 
 entire turning range, 
 and as the shaft is 
 squared, the steering arm 
 can be removed and the 
 wear taken up by turn- 
 ing the wheel through 
 an angle of 90 degrees, 
 and another quarter sec- 
 tion brought into action. 
 The thrust is taken on 
 ball bearings in either 
 direction. The controls 
 consist of a stationary 
 tube on top of which is 
 mounted a cylindrical 
 box, with a horizontal 
 slot in one side through 
 which the control levers 
 
 STEERING 
 
 WHEEL. 
 
 LEVER 
 
 LEATHER BOOT 
 LL SOCKET 
 PRING 
 
 BALL ON STEERING ARM OF AXLE 
 
 FIG. 179. Natco Steering Column. 
 
 extend. Each control lever has an extension, which carries a 
 friction segment, being pressed against the inner wall of the 
 C3^1indrical housing by a spring. The lower end of this stationary 
 tube is rigidly attached to the housing so that it cannot rotate. 
 
206 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 A shaft and tube pass through the former to which the upper and 
 lower levers are attached. 
 
 The Natco steering gear (Fig. 179) is also of the worm and 
 wheel type with suitable ball bearings to take the thrust of the 
 worm, while a thrust button takes care of the wheel thrust. The 
 housing is made in one piece with openings for introducing the 
 worm and wheel. In this construction the steering shaft is also 
 used as the mast; however, the wheel is attached to the shaft by 
 bolts and flanges. But one control is provided, with the lever 
 located above the hand wheel; however, instead of passing the 
 control shaft through the case, the movement of the control lever 
 is transmitted externally by means of a double thread screw or 
 cam. The steering shaft has slots on opposite sides directly above 
 
 FIG. 180. Vulcan Steering Gear. Worm and Sector Type. 
 
 the housing. These are enclosed by a collar which fits over the 
 steering shaft and carries two dowel pointed screws, which set in 
 threads of the cam. A fork rests on this collar and any move- 
 ment of the control lever will tend to raise or lower this collar, 
 carrying with it the fork which is connected to the carburetor. 
 
 Screw and Nut Type (Fig. 177) illustrates a screw and nut 
 type of steering used on the Pierce 5-ton chassis. The solid 
 steering shaft has the hand wheel keyed to its upper end and a 
 multiple square threaded screw at its lower end. This screw 
 actuates a nut with trunnions on its outside which carry die cast 
 trunnion blocks that slide within the jaws of a forked lever, 
 keyed to the steering ball lever shaft. The housing is divided 
 horizontally and carries suitable ball thrust bearings, which are 
 
STEERING GEARS 
 
 207 
 
 adjustable from the lower end of the housing. The spark and 
 throttle controls are of the ratchet and sector type mounted out- 
 side of the column on the steering column mast. 
 
 Another screw and nut type of steering gear which is used on 
 a number of trucks is the Ross, shown in Fig. 181. The hollow 
 
 FIG. 181. Ross Screw and Nut Type Steering Gear for Fore and Aft 
 
 Steering. 
 
 steering shaft carries a steel screw at its lower end mounted be- 
 tween two ball bearings to take up its end thrust. This screw is 
 held to the shaft by means of a brazed joint and when the hand 
 wheel is turned a steel block or sleeve is given later movement. 
 This steel block or sleeve has a square external section and thereby 
 is prevented from turning by the housing. On each side of the 
 
208 MOTOE TKUCK DESIGN AND CONSTEUCTION 
 
 lower end of this sleeve, cylindrical recesses are turned, and cylin- 
 ders, which are free to rotate, are placed in these recesses. The 
 
 cylinders have slots 
 milled in them which 
 receive the projecting 
 arms of the steering ball 
 lever shaft. 
 
 The control levers 
 are mounted above the 
 wheel and their shafts 
 pass through the steer- 
 ing shaft. The motion 
 of these levers is reduced 
 at the lower end by 
 means of bevel gears. 
 
 Cross Steering. All 
 of the gears depicted 
 above are best adapted 
 to fore and aft steer- 
 ing, although they may 
 in some cases be arranged 
 for cross steering. Fig. 
 182 illustrates the Boss 
 screw type of gear, es- 
 FIG. 182. Eoss Screw and Nut Type Steer- pecially designed for 
 ing Gear for Cross Steering. cross .steering on heavy 
 
 vehicles. The lower end 
 
 of the steering shaft is integral with a steel screw, which, when 
 turned by the hand wheel, gives a bronze sleeve longitudinal 
 motion. This bronze sleeve is threaded internally to receive the 
 steel screw and has spirals milled upon its external surface. The 
 housing has spirals cut on its internal surface which engage 
 with the spirals on the sleeve. The bronze sleeve in addition to 
 internal threads contains a number of straight key-ways. The 
 steering ball lever which projects half way up into the sleeve has 
 integral keys, so that when the sleeve is given rotative and lon- 
 gitudinal motion, it rotates the ball lever. The gear is provided 
 with ball-thrust bearings and an adjustment to take up wear, 
 and can be made semi-irreversible or irreversible, depending upon 
 the ratio of the threads. 
 
STEEKING GEARS 
 
 209 
 
 Drag Links. In Fig. 179 is shown a type of drag link used 
 on vehicles up to about two tons capacity. It has ball sockets 
 which fit over the ball on the steering arm of the axle. One of 
 the ball sockets is brazed or welded to the drag-link tube and has 
 an opening to receive another socket, which is retained by a nut 
 or cap. The steering gear end has a housing attached to the tube 
 which carries ball sockets and springs. These springs are intro- 
 duced in the drag link to reduce the shock. The ball end may be 
 introduced through holes in the housing and sockets or through 
 slots which extend to the end of the housing. 
 
 FIG. 183. Vulcan Drag Link. 
 
 The Vulcan drag link (Fig. 183) offers an example of the 
 type used on heavy vehicles. This consists of a link of solid 
 section threaded on both ends into housings which are divided 
 on the ball center. The ball sockets on both ends are provided 
 with cushion springs, while the caps of the housings are retained 
 by long studs. This tends to facilitate assembling especially 
 when the springs are heavy. 
 
 Some makers enclose these joints in leather boots, as shown 
 in Fig. 179, to hold grease and prevent dirt and grit from cutting 
 the ball surface. 
 
 As mentioned previously, universal joints are necessary at 
 both ends of the drag link, because the steering arm moves in a 
 vertical plane, and the knuckle arm in a horizontal plane, but in- 
 stead of the ball and socket joints, forked joints are sometimes 
 used. This type of joint was illustrated in the preceding chap- 
 ter. They are somewhat simpler in construction and present 
 larger bearing surfaces. However, they are more difficult to en- 
 close and cannot take up wear automatically. 
 
 15 
 
CHAPTER XV 
 MOTOR TRUCK FRAMES 
 
 THE chassis frame practically forms the foundation of a com- 
 mercial car, since all the power-transmitting and other units are 
 attached to it. It is often referred to as the backbone of a com- 
 mercial car. Its construction depends to some extent upon the 
 general scheme of the chassis layout, the construction of power- 
 transmitting units and their mounting, as well as the method of 
 final drive, wheel base, etc. 
 
 When the commercial car was first introduced, comparatively 
 little attention was paid to the frame, as other things such as the 
 power plant, axles, etc., were deemed of greater importance, 
 hence the frame received slight consideration. However, after 
 experiencing considerable difficulty, due to accidents and other 
 failures which were traced directly to poor frame construction, 
 commercial car builders discovered that frames could be designed 
 with greater strength and with less weight if the problem was 
 given proper consideration. 
 
 Unit Power Plants and Flexible Mounting. The constant 
 trend of obtaining perfect alignment for the engine, clutch and 
 transmission has resulted in the adoption of the unit power plant 
 on some models, while in others, particularly, of the heavier type, 
 flexible mounting of the units has been resorted to. In fact, re- 
 gardless of unit construction, all individual units are generally 
 flexibly mounted to some degree, in order to relieve them of the 
 heavy stresses due to frame weaving when the road wheels mount 
 an obstacle on the road surface. However, since this subject of 
 power plant mountings is of considerable importance, this will 
 be discussed in detail in the succeeding chapter, the author con- 
 fining this chapter to the construction of the frame. In discussing 
 this subject, it may be necessary in some cases to refer to the gen- 
 eral chassis construction in order to clearly depict each type. 
 
 The most prominent types of truck frames may be divided 
 into three classes, according to their popularity : ( 1 ) The pressed 
 steel frame, (2) the structural channel frame, (3) the structural 
 I-beam frame. These may again be divided into various classes, 
 
 210 
 
MOTOR TRUCK FRAMES 211 
 
 depending upon the general construction and material as well as 
 the distribution of the main units. 
 
 The Pressed-steel Frame. The pressed-steel frame is quite 
 popular on all types of vehicles and is now universally used on 
 vehicles up to and including those of 5-ton capacity. Structural 
 channel and I-beam frames are still used by a number of makers ; 
 however, the pressed steel frame is rapidly gaining favor and 
 from present indications will eventually replace the other types. 
 
 In discussing the advantages and disadvantages of the various 
 types, the pressed steel frame may be mentioned as being lightest 
 in weight for equal strength of the structural or rolled channel 
 and I-beam section, while its cost is somewhat higher, due to the 
 use of heat treated material to obtain maximum strength. The 
 cost varies with the section, material and the nature and extent of 
 bending. 
 
 The straight side rail is of course the cheapest construction; 
 however, when conditions permit, this is usually tapered at the 
 front and the rear and the forward end is sometimes formed to 
 receive the spring hanger. When the seat is placed above the 
 engine this taper is usually very short, permitting the paying 
 load to be carried well to the front. Bumpers are sometimes pro- 
 vided to protect the chassis, these may either be formed integral 
 with the frame or attached to it by castings. 
 
 When the side members are inswept to permit a short turning 
 radius, it is necessary to make the flanges of the side rail of con- 
 siderable width at this point, tapering gradually toward the rear, 
 to provide the proper strength at the point of offset. 
 
 Cross Members. Cross members are usually made of the same 
 material as the side rails and when pressed have integral gussets, 
 this, of course, is not possible with the rolled sections so that the 
 separate gusset plates must be used, thus placing the strain on 
 the rivets, instead 'of on the cross member. 
 
 These frames of either type are used in both flexible and rigid 
 constructions. While both kinds of material are subject to heat 
 treatment, it is generally conceded that pressed steel is a higher- 
 grade metal than rolled stock. Owing to its temper it will stand 
 a certain amount of bending which would give rolled stock a 
 permanent set or crack it. It is alleged that pressed steel is more 
 sensible to vibration, in that it will crystallize sooner than rolled 
 steel under similar conditions. Instead of being built up rigid, 
 as are rolled-steel frames, the pressed-steel frame may be built up 
 
212 MOTOE TKUCK DESIGN AND CONSTEUCTION 
 
 flexible, so that instead of taking the vibration dead, as well as 
 sudden shocks, it gives to them and transmits them to other* parts, 
 so that the individual vibrations in any part are reduced by dis- 
 tribution. The pressed steed flexible frame may also be made 
 lighter for its strength because of its flexibility. 
 
 The Rigid Frame. The rigid frame, too, has advantages, 
 whether it is of pressed steel or rolled stock. It permits the body 
 to be secured rigidly to it and as it does not give to the inequali- 
 ties of the road, there is no racking of the body. An advantage 
 of rolled stock is its cheapness, except of course in the lighter 
 models of the assembled type for which frames can be purchased 
 at low figures. Another advantage of rolled stock is the ease 
 with which the wheelbase can be altered. The maker using this 
 type of frame may with little additional expense give customers 
 a shorter or longer frame than standard. 
 
 It is possible to alter the pressed-steel frame in length by cut- 
 ting off from the maximum length, although this disturbs the 
 nice proportioning of the frame for stresses, one of the important 
 advantages of this type. 
 
 Effect on Springs. The effect of frame construction upon the 
 design and duty of the springs must also be considered. This 
 feature is not generally understood, but has an important bearing 
 
 ^m YT-- ' 
 
 vrvr-i-.- ' ' ** ^^ 
 
 
 
 
 \ 
 
 
 
 
 
 
 * \^ct/ssrr 
 
 
 
 
 
 \ 
 
 i 
 
 vs 
 
 4^ -yr 
 
 k-yA^i- *< *^ 
 
 L. tfifr v \ s^ ^fcffe- 
 
 
 d 
 
 J( f ~^REAR SPRING BRACKETS. ^~~ T 
 
 r^^lMT SPRING BRACKETS--** 
 
 FIG. 184. Vim Del 
 
 ivery Car Frame. 
 
 upon the life of the vehicle. A rigid frame relies upon the springs 
 to allow for all axle displacement. If the front and rear wheels 
 on opposite sides be raised several inches simultaneously, the 
 frame is subjected to a torsional stress. If the frame is rigid, 
 springs of considerable camber must be employed in order to 
 absorb the shock without being bent past the limit of safety and 
 
MOTOR TRUCK FRAMES 
 
 213 
 
 sufficiently flexible to absorb all of 
 the shock without any tendency 
 to lift the other wheels from the 
 ground. For this reason a dif- 
 ferent type of spring is used on a 
 rigid chassis from that used on 
 flexible ones. 
 
 The flexible frame when diag- 
 onally opposite wheels are raised 
 does not impose all of the duty 
 on the springs, but warps and ab- 
 sorbs a part of the stress. For 
 this reason springs on flexible 
 chassis are usually flat or nearly 
 so, with a reduced amount of play. 
 Flexible construction also permits 
 the frame to be carried equally as 
 low as with the underslung spring, 
 and yet the spring is perched 
 above the axle, where it is more 
 nearly in line with the center of 
 gravity, thus reducing sidesway. 
 
 Details of construction such as 
 spring hangers, etc., Vary consid- 
 erably, as can be noted from the 
 descriptions of the various types, 
 which follow : 
 
 Specific Illustrations. The 
 Vim 4-ton frame (Fig. 184) il- 
 lustrates a construction of pressed 
 steel, with straight side rails and 
 cast spring hangers which are 
 riveted to the former. Owing to 
 its shortness on account of the 
 small size of the vehicle this frame 
 is unusually strong. 
 
 The Reo f-ton frame (Fig. 
 185) also employs straight-side 
 rails; however, these are tapered 
 and bent at the front end to re- 
 ceive the spring hanger. This il- 
 lustration shows in detail all parts 
 
214 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 which are riveted to the frame and also a rigid sub -frame con- 
 struction, which is set at an angle to provide as near as possible 
 a straight-line drive to the rear axle. All cross members are 
 provided with integral gussets, while pressed-steel parts such as 
 step hanger, body brackets, etc., are used to keep the weight 
 within reasonable limits for this size of vehicle. One-ton frames 
 are built along similar lines. 
 
 
 TRfGAL Gusserrs 
 
 DOUBLf 
 CROSS MEMBER 
 TO BRACE FRAME 
 
 STfiAIGHr SIDE BAIL 
 
 FIG. 186. Fremont Mais Pressed Steel Frame. 
 
 Fig. 186 depicts the Fremont Mais 1^- to 2-ton frame, with 
 straight-side members, bent at the front end to receive the spring 
 brackets. In this construction, the scheme is to eliminate unnec- 
 essary cross members, so that the frame forms a flexible construc- 
 tion; however, it presents an excellent method of providing 
 strength at the point where the drive, which is taken by the 
 springs, is transmitted to the frame. This is accomplished 
 by placing two cross members together to form an I-beam 
 structure. 
 
 Fig. 187 shows the flexible frame construction, which is char- 
 acteristic of all Pierce worm-drive trucks. The side members 
 are pressed steel and taper at both ends, the front being bent to 
 form the spring hanger, while the bumper is also attached at this 
 point. But two cross members are used, as such parts as the 
 spring brackets and torsion rod support are used for this pur- 
 pose, while the rear member is of tubular section. A brace of 
 cross shape serves to form a flexible support at the point of drive. 
 In this construction the drive is taken through radius rods at- 
 tached to a bracket which also forms the spring bracket and car- 
 ries the tubular member from which the torque arm is supported. 
 
 The Locomobile trucks are also also worm-driven and are 
 equipped with radius rods and torque arm to take the torque and 
 driving thrust; however, the frame (Fig. 188) is made of rigid 
 
MOTOR TRUCK FRAMES 
 
 215 
 
216 MOTOK TKUCK DESIGN AND CONSTRUCTION 
 
 construction. It is made of pressed steel with side members 
 tapered at both ends and cast spring brackets riveted to the side 
 rails. The forward cross member forms a bumper, while the re- 
 maining members support the transmission and service brake 
 
 FIG. 189. DeKalb Pressed Steel Frame Inswept at Eear. 
 
 and form braces at the points of spring anchorage to the side 
 rails. The extreme rigidity of this construction can be noted by 
 the numbers of cross members and the method of reinforcing the 
 rail with an etxra channel insert. 
 
 Fig. 189 depicts the De Kalb 4-ton frame, which is also of 
 pressed steel with tapered side members. This frame is of con- 
 ventional design with the exception of the side rails, which are 
 inswept along side the rear springs much the same as the con- 
 ventional side member is narrowed from the dash forward to re- 
 duce the turning radius. Through this feature lower body car- 
 
 [3h ?-ri r-ra 
 
 ~T REAM 
 
 .^CAST STEEL CROSS MEMBERS ~~ 
 
 1 
 
 Lr 1 
 
 
 
 
 
 f 1 
 
 t tf 
 
 ( 
 
 V 
 
 f/fOHT SPRING BRACKETS' 
 
 JACKSHAFT 
 
 FIG. 190. U. S. Structural Channel Frame. 
 
 riage is obtained than would be possible otherwise. It also pro- 
 vides ample clearance for the radius rods, chains and springs. 
 The flange width is increased at the point of offset to provide 
 proper strength. 
 
MOTOR TRUCK FRAMES 
 
 217 
 
 The United States 3-ton frame (Fig. 190) is an illustration 
 of the structural or rolled channel frame, combined with steel 
 castings and a construction in which each unit is mounted as 
 flexibly^ as possible. The forward three cross members are steel 
 castings, the fourth of I-beam section rolled steel and the rear of 
 channel shape rolled steel. The front-spring hangers are formed 
 integral with the front cross member, which is in two halves, 
 bolted together at the center. 
 
 FIG. 191. Knox Tractor Frame. 
 
 The Knox tractor frame (Fig. 191) is made from rolled steel 
 of channel shape; however, it is comparatively short, as the rear 
 axle is attached to the frame by means of cantilever rear springs. 
 Thus the frame merely extends far enough to carry the support 
 on which the spring pivots. The illustration shows the combined 
 jackshaft and brake support bracket and other parts which are 
 riveted to the frame. Large gusset plates are used at the front 
 and rear end, while the front cross member extends to each side 
 and is curved to form the bumper. 
 
 The 3-ton Yelie frame (shown in Fig. 192) is built up from 
 rolled steel of I-beam section, with subframe members of chan- 
 
218 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 11 
 
 &d 
 
 I 
 
 nel section. It is of the rigid 
 type well braced, and provided 
 with heavy gusse't plates. The 
 front cross member is bolted in 
 position for easy access to the 
 power plant. Diagonal braces of 
 channel section are placed between 
 the third and fourth cross mem- 
 bers for stiffening the frame. It 
 is claimed that I-beam section pro- 
 vides a much heavier and stronger 
 frame, due to greater width of the 
 flanges. 
 
 To eliminate the braking of 
 frames, there seems to be a gen- 
 eral movement against drilling 
 any rivet or bolt holes in the bot- 
 tom flanges of the side rails. In- 
 stead of drilling the flanges in 
 attaching the body and frame 
 brackets, the vertical section of 
 the frame is drilled. There is less 
 weakening of the frame by this 
 process. There is also a decided 
 tendency toward the use of 
 straight-side rails. A novel fea- 
 ture which accomplishes this is 
 used on the Nash trucks and illus- 
 trated in Fig. 193. Instead of 
 tapering the frame at the front 
 end as is usual by carrying the top 
 flange straight, the taper is accom- 
 plished by keeping the bottom 
 flange straight and tapering the 
 top gradually down to the spring 
 horn. Bolting instead of riveting 
 frame members and castings is also 
 receiving serious consideration at 
 present. 
 
 Structural steel of channel or 
 I-beam section is bought from the 
 steel mills in stock lengths. It is 
 
MOTOR TRUCK FRAMES 219 
 
 usually manufactured from Bessemer steel, afterward subjected 
 to open hearth process in which it is saturated with carbon, to 
 certain specifications for certain uses. 
 
 FIG. 193. Nash Frame showing Taper of Upper Flange. 
 
 Pressed steel is purchased in sheet form, cut to the proper 
 shape in the flat and then pressed into channel form under great 
 pressure. It is made of steel rolled into sheets ; it is made some- 
 what closer grained, and there is no breaking of the flake in the 
 rolling operation. The pressed steel frame permits of greater 
 simplicity in assembling, since parts can be easily bolted or 
 riveted to it. 
 
CHAPTER XVI 
 
 POWER PLANT MOUNTINGS 
 
 AN interesting problem in connection with commercial car 
 designing which merits careful consideration is that of mounting 
 and arranging the power plant so as to protect it from stresses 
 caused by frame weaving, due to road irregularities. Vibration 
 is another factor of considerable magnitude that must be consid- 
 ered, while provision must also be made for torque reaction. 
 
 Power-plant mounting is being freely discussed and there 
 seems to be a general tendency toward some form of flexible sup- 
 port, so that sufficient freedom is given the engine, while others 
 resort to a spring mounting, which combined with a flexible sup- 
 port, protects the power plant from vibration and frame weaving. 
 
 Opinions differ greatly as to the correct mounting, some 
 maintaining that the usual method of bolting down the two rear 
 engine arms rigidly to the side rails of the frame does not give 
 the engine sufficient freedom, even if a flexible support is pro- 
 vided at the forward end. Others take the opposite view, claim- 
 ing that the front flexible support is sufficient. There are also 
 some engineers who claim good results can be obtained by a rigid 
 central support at the front end, as this practically gives a three- 
 point support, and permits frame weaving to be taken up by the 
 cross member which supports the forward end of the engine. 
 
 The material give of the cross member should absorb severe 
 stresses and also hold the engine more rigidly against torque 
 reaction. 
 
 If the engine is mounted with a pivoted support at the for- 
 ward end, the torque reaction caused by an explosion in the front 
 cylinder, must be transmitted through the crankcase to the rear 
 engine arms before it reaches the frame. However, if the for- 
 ward support is of the rigid type, the stress goes to the frame 
 direct. 
 
 In addition to the flexible front support, some makers also 
 provide swivel supports for the rear arms, so that all the torque 
 reaction must go to the rear arms, but no frame distortion can by 
 any possibility put a stress upon the crankcase. Larger and more 
 massive engine arms are also being used, thus increasing the 
 efficiency of the present mountings. 
 
 220 
 
POWER PLANT MOUNTINGS 
 
 221 
 
 Coil springs of considerable strength are also used under the 
 front or rear supports, and these absorb some of the stress created 
 by frame weaving, while they can also be arranged to absorb 
 some vibration. 
 
 An important point with a rigid mounting is the method of 
 securing the rear arms to the side rails of the frame. In this case, 
 the engine must be held securely, and the frame must not be ap- 
 preciably weakened, while the arrangement must be such that the 
 supporting arms can be quickly freed when it is desired to re- 
 move the engine from the chassis. 
 
 In the unit power plant the transmission is supported from 
 the flywheel housing, but in the amidship position, it is usually 
 mounted on a three-point support, so that it has a certain degree 
 
 FIG. 194. A Prominent Type of Flexible Support, which may be Adapted 
 to Either the Engine or a Unit Power Plant. 
 
 of flexibility to resist frame weaving. In some cases where a 
 flexible subframe is used for the motor, this is also arranged to 
 support the transmission. For midship mounting, cross mem- 
 bers of the frame are usually used, so that the forward support 
 forms the flexible member, while the rear carries the two rigid 
 supports. 
 
 One of the most prominent types of flexible supports is shown 
 in Fig. 194, which may be adapted to either the engine or a unit 
 power plant. This particular illustration represents the Globe 
 1-ton truck, equipped with a Continental engine. In this con- 
 struction two cast arms integral with the flywheel housing, form 
 the two rigid points of support. These are set on hangers, riveted 
 
222 MOTOE TKUCK DESIGN AND CONSTKUCTION 
 
 to the side rails of the frame, while bolts pass vertically through 
 both, to hold the power plant in position. 
 
 The third point of support is at the front end of the engine, 
 and consists of a bracket fitting over a finished surface, on the 
 hub extension of the gear cover plate. A cross member passes 
 under this, and has the bracket fastened to it by two bolts. 
 
 FIG. 195. A Three-Point Main Frame Mounting Employed on the Riker 
 
 Trucks. 
 
 This engine is also used on the Denby trucks, and is mounted 
 in a similar manner, but in order to provide more flexible rear 
 supports, one bolt on each side is fitted snugly and provided with 
 a coil spring, the others being a loose fit. 
 
 Another type of three-point mainframe mounting is shown in 
 Fig. 195, being employed on the Eiker commercial cars. In this 
 construction, a heavy drop forged member is attached to the 
 crankcase at the rear by studs, which pass clear through the case. 
 These studs are so close together that considerable freedom is ob- 
 tained by this supporting member, through the elastic extension 
 of the studs, and the elasticity of the forged member. The for- 
 ward end is also supported by a forged member ; however, this is 
 pivotally arranged in a bracket bolted to the crankcase. Metal 
 filling blocks are fitted into the side rails of the frame, and three 
 bolts in each end of these supports secure the engine to the frame. 
 The top flange of the supports overhangs the filling blocks, and 
 so relieves the bolts from the weight of the engine. 
 
 The Pierce 5-ton truck engine is also mounted in a similar man- 
 ner, while the Packard truck engines have a pivot mounting at 
 
POWER PLANT MOUNTINGS 
 
 223 
 
 the front end, and the rear end is supported by a large member 
 which is bolted to the flywheel housing. 
 
 An interesting and simple method of support is used on the 
 Union trucks (Fig. 196), which is covered by patent. The for- 
 ward support is of swivel type, consisting of a bracket fitting 
 over a hub extension of the timing gear cover. This bracket has 
 
 FIG. 196. Simple Method of Support used on the Union Trucks. 
 
 two lugs which rest on the upper flange of the cross member, so 
 that the weight is taken off the bolts that hold the bracket in 
 position. 
 
 The rear support is a large cast member bolted to the flywheel 
 housing, which has a trunnion formed on each side, and these fit 
 into brackets, that in turn are bolted to hangers riveted to the 
 frame side rails. This gives the engine somewhat greater free- 
 dom, and permits taking the torque reaction on the rear member. 
 
 The Signal truck has an unusual engine mounting (Fig. 197), 
 which is also covered by patent. In this construction, swivel sup- 
 ports are also used on the rear arms, for with such a layout the 
 torque reaction must all go to the rear arms, but no frame distor- 
 tion can by any possibility put a stress upon the crank case. A 
 bracket developed into spherical shape is bolted to the arms ex- 
 tending from the flywheel housing and supported by brackets 
 bolted to the frame members. The forward support is of the 
 pivoted type, similar to the Riker, having a drop-forged member 
 that is supported by coil springs and brackets attached to the 
 
224 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 frame members. A long stud 
 supports the springs above and 
 below the frame brackets, so 
 that the springs relieve the en- 
 gine of severe shocks and vi- 
 bration. 
 
 The Diamond T-trucks also 
 have a swivel rear support of 
 the ball-and-socket type, and 
 the front support is of the piv- 
 oted type, supported from a 
 channel section cross member, 
 which is also used to support 
 the radiator. 
 
 One of the chief difficulties 
 encountered in combining the 
 engine and transmission in a 
 single unit is due to the fact 
 that the flywheel is located be- 
 tween them and to enclose it 
 requires a great deal of metal, 
 adding both to the weight and 
 the cost. In commercial car 
 practice the four-cylinder en- 
 gine seems to have become the 
 standard and with these there is 
 a tendency to use a flywheel of 
 inadequate capacity, when it is 
 to be enclosed, which detracts 
 somewhat from the steady run- 
 ning qualities of the vehicle. 
 To overcome this, two expe- 
 dients may be resorted to. One 
 is to place the flywheel at the 
 front end of the engine, but 
 there are a number of objections 
 to this practice. The purpose 
 of this flywheel is to equalize the 
 torque of the engine before it is 
 transmitted to the transmission 
 and its logical place therefore 
 seems to be between these two 
 units. The forward location also 
 
POWER PLANT MOUNTINGS 
 
 225 
 
 places it in a position where it can easily be injured, while the 
 strains on the tires are increased and the clearance between the 
 engine and front axle is materially reduced. 
 
 On the Dorris commercial cars all the features of an open fly- 
 wheel are retained as illustrated in Fig. 198, by joining the en- 
 gine and gear box by a large yoke which permits the use of a 
 large flywheel and also affects a considerable saving in weight. 
 
 2 a" FLY WHEEL 
 
 YOKE 
 
 FIG. 198. The Dorris Unit Power Plant. 
 
 The method of mounting the engine in the United States 
 motor trucks is illustrated in Fig. 199. The engine is mounted 
 on a subframe, the front cross member of which extends into the 
 side members of the frame. This cross member has ends that 
 form a yoke into which are placed heavy coil springs, retained by 
 a long bolt, passing through a bracket riveted to the frame, thus 
 utilizing the springs to absorb severe shocks and vibration. 
 
 A 5-in. spherical bearing riveted to the rear of the subframe 
 forms the rear support. This rests on a large cast cross member, 
 which is dropped considerably at the center. The support is on 
 the upper side of this cross member, thus providing a very flex- 
 ible mounting. 
 
 The larger sizes of Kissell Car trucks also have the power 
 plant mounted on springs at both ends, with provision for flex- 
 16 
 
226 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 ible mounting incorporated in the rear supports as depicted in 
 Fig. 200. The engine is mounted upon a pressed steed subframe 
 having cross members at both ends, which are dropped consid- 
 
 FIG. 199. Sub-Frame Arrangement used on the United States Trucks. 
 
 erably at their center. The front cross member has two pressed 
 steel brackets which rest on heavy coiled springs placed inside 
 
 -FRONT SUPPORT 
 
 FIG. 200. Kissel-Kar Six-Ton Sub-Frame Mounting. 
 
 of the front cross member of the main frame. Another spring is 
 placed below the flange of this cross member, a bolt being used to 
 hold both springs in position. In this way the movement of the 
 
POWER PLANT MOUNTINGS 
 
 227 
 
 MAIN FRAME 
 
 HINGE 
 
 MA/M FRAME 
 
 forward end of the subframe is controlled in both directions. 
 The rear support is formed by brackets riveted to the subframe 
 members, which have a 
 
 T "I J "I J J_ ^ * I"~ 1 
 
 m 
 
 ball-shaped end that rest 
 on ball sockets placed 
 within a bracket riveted to 
 the main frame members. 
 These ball sockets are pro- 
 vided with springs, to re- 
 lieve the power plant of 
 shocks due to vibration 
 while the ball permits a 
 certain degree of flexibility 
 when the frame twists. In 
 reality this is a four-point 
 suspension which retains 
 all the features of a three- 
 point suspension. 
 
 The same principles of unit power-plant mounting may be 
 applied to vehicles in which the engine or both engine and trans- 
 mission are carried on a subframe. Fig. 201 illustrates this 
 feature applied to Mogul trucks. The frame has a front cross 
 member which carries a bracket to form the bearing for the third 
 point of support. The subframe is also provided with a cross 
 
 member and a bearing 
 bracket, so that a hollow 
 pin can be inserted. This 
 is retained by a large 
 nut, having a hub, which 
 together with the pin 
 
 WVOT 
 
 H/NGE 
 
 FIG. 201. Mogul Power-Plant Mounting. 
 
 MAIN 
 FRAME 
 
 SUPPORT 
 
 FIG. 202. 
 
 Three-Point Suspension of the 
 DeKalb Sub-Frame. 
 
 forms the bearings for 
 the starting crank. The 
 rear ends of the sub- 
 frame being supported 
 from a frame cross member. 
 
 A similar construction (Fig. 202) is used on the Dr. Kalb 
 commercial cars. However in this case the hinge is placed at the 
 front end of the subframe members, while the rear end has a 
 large drum which forms a single hinge. Fig. 203 illustrates a 
 sectional view of this rear support and also illustrates the method 
 of supporting the front end of the transmission from this point. 
 The transmission is bolted to the jack shaft and has a long torque 
 
228 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 INGE 
 
 tube extended to this third point of support, which is of spherical 
 
 form. 
 
 The principle of three-point suspension in the Blair trucks 
 
 (Fig. 204) is even carried on to the rear axle. In this construc- 
 tion the subframe is hinged 
 to the main frame in front 
 by steel castings and heavy 
 hardened and ground steel 
 pins. At the rear it is 
 hinged at right angles to the 
 worm-drive-axle housing. It 
 
 O 
 
 is claimed that this system 
 renders the subframe that 
 carries the power plant flex- 
 ible to any position, main- 
 taining perfect alignment in the transmission of power. It pro- 
 vides a straight-line drive under all conditions, and almost en- 
 tirely eliminates universal joints in the drive. 
 
 3PHEft/CAL BEARING 
 
 FIG. 203. DeKalb Sub-Frame and 
 Transmission Support. 
 
 FIG. 204. Sub-Frame Arrangement used on the Blair Trucks. 
 
 Flexible mountings are also applied to transmissions when 
 these are located amidship. An excellent example of this is the 
 United States mounting (Fig. 199), in which spherical or ball- 
 and-socket joints are used at three points, one at the forward end, 
 and one at each side in the rear over the jack-shaft housing. 
 
POWER PLANT MOUNTINGS 
 
 229 
 
 On the Packard trucks the transmission (Fig. 205) is sup- 
 ported by two pressed-steel cross members. The forward end is 
 bolted to a cross member, which has a machined surface that fits 
 over the housing, which supports the forward or main shaft of 
 the transmission. The rear end is free and pivotally mounted in 
 the brake anchor, which is attached to the cross member. 
 
 FIG. 205. Method of Supporting- the Transmission on a Packard Truck. 
 
 On the Federal truck a modified three-point support is used. 
 The transmission case has four lugs, two at each end, and these 
 support the transmission case, being attached to two cross mem- 
 bers. The two lugs at the front are close together, and prac- 
 tically produce the same effect as a single point. 
 
 Three-point support is also used on several other trucks, the 
 forward support being of the pivot type while the rear is either 
 directly mounted from a cross member or by brackets attached to 
 the transmission. 
 
 The advisability of providing a long life for the power plant 
 will be endorsed by all users of commercial cars, and since this 
 feature can be accomplished with little added expense, it would 
 seem to be a step toward reducing maintenance cost. There are 
 very few makers at present who do not provide a certain degree 
 of flexibility in the mounting of their power plants. 
 
 These few contended that there is little to be gained through 
 this feature; how r ever, it is not to be denied that for commercial 
 cars, this feature presents several advantages. 
 
CHAPTEK XVII 
 
 SPKINGS AND SPEING SUSPENSIONS 
 
 COMMERCIAL car bodies are mounted upon the chassis frame, 
 the latter being supported on the axles through the intermediary 
 of steel springs. These springs are built up of a number of 
 plates varying in length and are used exclusively to support the 
 body, although coil springs are used as auxiliaries. 
 
 The upper leaf of this spring usually has an eye at each end 
 for connection to spring brackets on the frame, or shackles. In 
 some few cases the ends are left flat and fit in brackets so that 
 the frame rests directly on them. The balance of the spring con- 
 sists of a number of shorter leaves, the lengths of which de- 
 crease uniformly, except in cases when they are required to carry 
 very heavy loads, in which the first two or three leaves are of the 
 same length. The various leaves are held together by a center 
 bolt or a band. 
 
 The method of frame connection depends upon the type of 
 spring and various other factors, while the axle connection is 
 usually made by box clips and a spring seat on the axle. This 
 seat is sometimes called a perch, and may be formed integral, or 
 attached to the axle. 
 
 Spring Types. The simplest type of spring is the semi- or 
 half-elliptic type, while all other types are made up wholly or in 
 part of the former. They may be termed combinations of the 
 semi-elliptic type. 
 
 The three-quarter-elliptic type consists of a semi-elliptic lower 
 member and a quarter-elliptic top member. These two members 
 are joined by shackles and bolts at one end. This type of spring 
 is used on pneumatic tired vehicles only at present. 
 
 The full-elliptic spring consists of two semi-elliptic members 
 joined at both ends by bolts or shackles and bolts. 
 
 The three-quarter platform spring consists of two semi-elliptic 
 side members and one semi-elliptic cross member, the side mem- 
 bers being joined to the cross members by shackles and bolts. 
 This type is ordinarily termed the platform spring, since the true 
 full platform spring consisting of two side and two cross semi- 
 
 230 
 
SPKINGS AND SPRING SUSPENSIONS 231 
 
 elliptic members is not adaptable to the ordinary chassis con- 
 struction. 
 
 Auxiliary springs consist of a half-elliptic with plain ends. 
 The cantilever spring carries the weight at its small end and may 
 either be quarter-elliptic; in which the big end is secured to the 
 frame or a semi-elliptic; in which case it has a pivot support on 
 the frame at or near its center, and is connected to the rear axle 
 at its rear end. 
 
 There are also various other combinations; however, they are 
 not employed at present, and consequently are not within the 
 scope of this work. 
 
 Semi-elliptic a Favorite. Regardless of capacity, the semi- 
 elliptic suspension is a decided favorite. It is simple, and if the 
 length, width and other dimensions are proportioned correctly, 
 nothing better than the semi -elliptic spring for front and rear 
 suspension could be desired. 
 
 The remaining spring suspensions employed at present may 
 be classified as follows: Semi-elliptic front, full-elliptic rear; 
 semi -elliptic front and three-quarter-elliptic rear; full-elliptic 
 front and rear; semi-elliptic front and three-quarter platform 
 rear; full-elliptic front and platform rear. 
 
 Another point worthy of note is the substitution of the true 
 sweep spring and the elimination of the double sweep spring. 
 Having a simple curve, the true sweep spring is easy to fit, and 
 spring makers recommend them on this account. The double 
 sweep spring is simple to mount and has a legitimate place on 
 every truck as an auxiliary or overload spring. Comparison of 
 these two types may be made by referring to Figs. 206 and 207, 
 the former being a true sweep and the latter a double sweep 
 spring. 
 
 Until recently, very few springs were equipped with bumpers ; 
 however, in most cases these are in the form of coil springs, and 
 on some vehicles they are made of a heavy square section. 
 
 The general construction of the various types can readily be 
 understood by referring to accompanying illustrations; however, 
 the method of frame suspension and axle mounting warrants dis- 
 cussion. 
 
 De Kalb Springs. Fig. 206 illustrates the De Kalb rear 
 spring, which is of the semi -elliptic true sweep type. These are 
 placed outside of the frame to permit carrying the frame low, 
 and the main leaf has an eye at each end which is connected to 
 
232 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 the frame by means of shackles and bolts through brackets riveted 
 to the frame. All bearing surfaces are provided with removable 
 bushings and grease cups. The leaves are held together by means 
 
 FIG. 206. DeKalb Spring Mounted Outside of Frame and Over Axle. 
 
 of a steel outer band which is shrunk over them. The spring is 
 attached to the axle by means of a spring seat which is mounted 
 on the axle spindle and prevented from turning by a set screw. 
 Box clips of square sections, placed at an angle are used to hold 
 the spring to its seat. Two nuts are used to hold the spring rigid, 
 while the upper ends of the clips are held in position by a pres- 
 
 FIG. 207. Mogul Six-Ton Rear Spring with Tlain Ends Showing Method 
 of Mounting on Axle. 
 
 sure block on the top of the spring which fits snugly over the 
 center band. 
 
 The front spring is of similar construction; however, the 
 front end of this is attached directly to the front bracket, while 
 the rear end is shackled to its bracket. The necessity of directly 
 
SPRINGS AND SPRING SUSPENSIONS 
 
 233 
 
 connecting the forward end of a front spring to frame is due to 
 the fact that this is the 
 
 is 
 
 only connection between the 
 frame and the axle, the 
 spring being utilized to 
 hold the front axle in posi- 
 tion. This is also true of 
 the forward end of a rear 
 spring when the torque and 
 driving thrust is taken 
 through the spring. This 
 feature was explained in a 
 previous chapter on the final 
 drive. 
 
 SPRING BAND 
 
 CUP 
 
 SPRING 
 
 SPRING 
 SEAT 
 
 AXLE 
 
 FIG. 208. 
 
 Mogul Springs. In Fig. 
 207 is shown the Mogul 
 6-ton rear spring, which is 
 of the semi-elliptic double 
 sweep type with plain 
 ends. These ends fit between the webs of the frame bracket, 
 which has a hardened steel plate resting on the spring. In this 
 case the spring seat is also mounted on the axle spindle ; however, 
 
 Mogul 6-Ton Front Spring 
 Mounting. 
 
 SPRING CLIPP 
 
 AXLE HOUSING 
 AXLE DRIVE SHAFT. 
 SPRING SEAT 
 SPRING BAND 
 
 FIG. 209. Chase Underslung Spring Shackled at one End. 
 
 in place of the usual box clip, four heavy bolts with a T-shaped 
 head are used. The bolts fit into grooves formed into the walls 
 of the spring seat and the heads of the bolts fit into rectangular 
 holes cast into the seat. Two flat bars are used as a pressure block 
 
234 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 and are retained by washers and nuts. The front spring is con- 
 nected to the frame at the forward end by an eye and a shackle 
 bolt, while the rear end is plain and rests against a hardened 
 plate on the bracket. The method of axle mounting is similar to 
 the rear; however, clips are used in place of bolts, while the 
 spring seat is a steel casting, which fits over the axle as shown 
 in Fig. 208. The clips pass through holes in the seat proper 
 which coincide with grooves cut into the upper flange of the axle. 
 Tapered washers and nuts hold these together. 
 
 Chase Springs. On the Chase worm-driven models, the rear 
 springs (Fig. 209) pass under instead of over the axle, and also 
 take both the torque and the driving thrust. For this reason it 
 is necessary to rigidly connect the front end of the spring to the 
 
 FIG. 210. I.H.C. Full-Elliptic Front Spring. 
 
 frame, while the rear end is shackled to compensate for elonga- 
 tion under load. Conditions are reversed in the axle mounting, 
 as the pressure block is placed under the spring and the spring 
 seat over it. These are held together by clips of U-shape which 
 pass over the axle. 
 
 Fig. 210 depicts the full-elliptic front spring used on the 
 I.H.C. 1,000-lb. vehicles. They are clipped to both the frame and 
 the axle. This type of spring consists of two semi-elliptic mem- 
 bers, one mounted above the other, and are connected at their 
 ends by bolts. This type is also employed on the rear end of 
 these vehicles; however, instead of rigidly connecting the upper 
 
SPRINGS AND SPRING SUSPENSIONS 
 
 235 
 
 PRESSURE 
 
 SPFf/NG CLIP 
 
 FRAME 
 
 member to the frame ; this is pivoted on a shaft as shown in Fig. 
 211. A bracket is attached to the frame, through which the shaft 
 passes. The upper spring seat pivots on this shaft and has the 
 spring clipped to it as 
 shown. The object of piv- 
 oting the upper end of the 
 rear spring is to compen- 
 sate for the spring play 
 since the only connection 
 between the axle and frame 
 with this type of spring is 
 through the radius rods. 
 
 Mack Springs. Fig. 212 
 
 illustrates the three-quar- 
 ter platform rear springs 
 used on the heavy duty 
 Mack trucks. The rear 
 ends of the two side mem- 
 bers are connected by double shackles consisting of two substan- 
 tial U-shaped members which are hooked together, the same as 
 on numerous horse-drawn vehicles. 
 
 SPRING 
 
 EAT 
 
 FIG. 211. Method of Mounting I.H.C. 
 Full-Elliptic Rear Spring. 
 
 FRAME SIDE MEMBER 
 
 FRAME CROSS MEMBER 
 
 FIG. 212. Three-Quarter Platform Spring used on Mack Heavy-Duty 
 
 Trucks. 
 
 Fig. 213 illustrates the overload or auxiliary spring which is 
 usually a semi-elliptic member of the double sweep type. It is 
 attached to a frame cross member at the center and the ends are 
 free so that they may make connection with a separate spring 
 when a predetermined load has been applied. 
 
 On the International Harvester Company's trucks, auxiliary 
 springs are provided which take action at a time when the main 
 springs are about to be overtaxed and prevent the load from 
 
236 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 coming in dead contact with the axle. These auxiliary springs 
 are of the quarter-elliptic type and are attached to the brackets 
 which take the driving strain at the front end of the spring. The 
 
 FRAME CROSS MEMBER 
 PfVNG CUP 
 PFUNG 
 
 FIG. 213. Overload Spring with Separate Seat. 
 
 rear ends of these auxiliary springs are free to bear on the pres- 
 sure blocks of the rear springs. This construction is illustrated 
 in Fig. 214. 
 
 Knox Tractor. The Knox Tractor employs an unusual 
 method of suspension, Fig. 215, which combines a cantilever and 
 semi-elliptic spring at the rear end of the frame. Heavy semi- 
 elliptic springs are attached to the rear axle with long clips and 
 carry the fifth wheel of the trailer. There is no connection be- 
 tween these and the tractor frame, so that they carry the weight 
 
 FIG. 214. I. H. C. Quarter Elliptic Overload Spring. 
 
 of trailer and load only. The tractor frame is mounted on a can- 
 tilever spring, having a pivot near its center and a shackle at 
 the front end. The rear end bears on a seat clipped to the rear 
 axle. This construction permits a flexible mounting for the 
 tractor, and also the carrying of very heavy loads on the trailer. 
 There is a great variety of methods of attaching the springs 
 to the frame and rear axle. Several methods have been illus- 
 trated above, while the following gives an excellent idea of the 
 attention that is being devoted to this vital point. 
 
SPKINGS AND SPRING SUSPENSIONS 
 
 237 
 
 FIG. 215. Knox Tractor Cantilever Rear Spring. 
 
 Selden Construction. The Selden construction (Fig. 216) has 
 a heavy pressure block which is grooved to take the U-shaped 
 clips and carries a heavy coiled spring 
 which contacts with a bracket riveted 
 to the frame and acts as a check for ex- 
 cessive deflections. Two of these coiled 
 springs are used one on each side. 
 
 The Vulcan 5-ton front springs 
 (Fig. 217) are mounted on a seat 
 forged integral with the front axle, 
 and are retained by long studs which 
 have a shoulder near their center and 
 by a drop-forged pressure block. 
 
 The Velie 3-ton vehicles have a 
 rear axle of round section and cast 
 spring seats which are held in position by a heavy bolt pass- 
 ing through the axle. The spring leaves are held together 
 by a center bolt which passes through the pressure block. Long 
 
 FIG. 216. Selden Spring- 
 Mounting 1 . 
 
238 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 SPRING. 
 
 FIG. 217. Method of Mounting 
 Vulcan Five-Ton Springs. 
 
 a heavy pressure block,while 
 the seat for the bumper is 
 also retained by the clips. 
 This construction is shown 
 in Fig. 221, while Fig. 222 
 illustrates the spring shack- 
 les and the method of con- 
 necting these to the frame. 
 This shackle is suspended on 
 a very large shaft extending 
 the full width of the frame 
 and supported by brackets 
 riveted to the frame. 
 
 box clips are used to attach the 
 spring to its seat, as shown in 
 Fig. 218. 
 
 Peerless Springs. On the 
 Peerless trucks the front springs 
 are mounted on a seat forged 
 integral with the axle, and are 
 retained by box clips. Fig. 219 
 illustrates this, and it will be noted 
 that a coil spring is attached to 
 the pressure block which acts as a 
 bumper. Under excessive deflec- 
 tions these springs strike the bot- 
 tom flange of the frame and ar- 
 rest the rebound motion of the 
 vehicle springs. 
 
 The Nash Quad also employs 
 a spring bumper which is made 
 of flat metal and is termed a vo- 
 lute spring. This is attached to a 
 bracket fastened to the pressure 
 block, as shown in Fig. 220. 
 
 The Gar ford worm- driven 
 models have the springs mounted 
 outside the frame and the bumper 
 springs, which are of square section 
 are mounted directly under the 
 frame side. The vehicle springs 
 are retained by U-shaped clips and 
 
 FIG. 218. Velie Three-Ton Rear Spring 
 Mounting. 
 
SPRINGS AND SPRING SUSPENSIONS 
 
 239 
 
 BUMPER 
 
 On the Selden trucks this shaft is replaced by a steel tube 
 
 which ties the brackets together but the 
 
 shackle is mounted on a separate stud. 
 In the Hotchkiss drive, when the 
 
 springs form the only connection be- 
 tween the frame and re'ar axle and the 
 
 drive is entirely dependent upon the 
 
 main leaf of the spring, there is danger 
 
 of spring breakage which will disable 
 
 the vehicle. In order to overcome this 
 
 disadvantage the Fulton and Garford 
 
 companies provide a three -point shackle 
 
 at the front end of the spring, as shown 
 
 in Fig. 223. This illustrates how the 
 
 main leaf is supplemented by the elon- 
 gated eye in the second leaf in caring 
 
 for the driving stresses, which also illustrates the method of caus- 
 ing the third and fourth leaves to 
 help to assist the two main leaves 
 in bearing the load. 
 
 FIG. 219. Peerless Front 
 Spring Bumper and In- 
 tegral Spring Seat. 
 
 BUMPER 
 
 Rebound Clips, In most cases 
 the vehicle springs are equipped 
 with rebound clips, the purpose 
 of these may be explained as fol- 
 lows : When the road wheel strikes 
 an obstacle in the road, the spring 
 near it is compressed, whereby 
 energy is stored up. Immediately 
 after the compression has ceased 
 the spring extends again, and if 
 the blow was a heavy one the re- 
 bound will carry the body far be- 
 yond its original position. This 
 rebound has a tendency to curve 
 the main leaf of the spring in 
 the reverse direction, and in order 
 to prevent any serious difficulty 
 
 it is necessary to transmit this shock to several of the leaves. 
 
 This is accomplished by the rebound clips which are riveted to 
 
 the shortest leaf which they surround and connected over the" 
 
 main leaf with a bolt. 
 
 FIG. 220. Nash Quad Spring 
 Mounting and Spring Bum- 
 per. 
 
240 MOTOE TRUCK DESIGN AND CONSTEUCTION 
 
 PRESSURE 
 BLOCK 
 
 FIG. 221. Method of Mounting Springs on the Garford Trucks. 
 
 FIG. 222. Garford Eear Spring Shackled Construction. 
 
SPEINGS AND SPEING SUSPENSIONS 241 
 
 FIG. 223. Fulton Three Point 
 Front Shackle. 
 
 Spring Alignment. Although the clips at the center of the 
 spring tend to hold the leaves in alignment, they alone are not 
 sufficient, and in order to prevent lateral motion of the leaves 
 some other provision must be 
 made. One of the most com- 
 mon methods is to raise a cen- 
 tral longitudinal rib on the 
 main leaves for a certain dis- 
 tance as shown in Fig. 209. 
 The rib of one leaf enters the 
 corresponding gutter on the 
 next. Another plan is to pro- 
 vide the leaves with lips at 
 right angles as shown in Fig. 
 210. 
 
 An objectionable feature of 
 the center bolt is that it mate- 
 rially weakens the spring and 
 quite often spring breakage 
 can be traced to the weakness 
 through the center bolt hole. 
 
 For this reason the center band, which is shrunk over the leaves, 
 is favored by a number of commercial car builders. 
 
 It is inadvisable to arrest abruptly the motion of a spring 
 that is suddenly deflected, and for this reason bumpers or check 
 springs, as they are sometimes termed, are used. Under exccessive 
 deflection these bumpers strike the lower flange of the frame or 
 brackets riveted to it for this purpose. The bumpers are so pro- 
 portioned that they yield under the load, producing a cushion 
 effect the same as rubber bumpers on pleasure vehicles. 
 
 Overload Springs. Overload springs may either be of the leaf 
 or coil type, and so arranged as to act only when the load on the 
 main springs reaches a certain amount. Below this load they do 
 not contact with their seat or wear plate. The wear plate may be 
 a separate platform, as illustrated in Fig. 213, or it may be 
 formed integral with the pressure block. When coil springs are 
 used, they are made of square section, attached either to a frame 
 cross member or the axle. Two such springs are used, one on 
 each side. 
 
 Spring Clips. The general desire to prevent breakage at the 
 center is seen in the liberal proportion of the pressure blocks and 
 spring clips. They represent the efforts of the various makers 
 17 
 
242 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 to provide a rigid connection between the spring and the seat. 
 There is a growing tendency to employ the U-shaped spring clip 
 which tends to exert an equal hold on each side of the spring, 
 consequently the tension is equally distributed when the nuts 
 are drawn up tight. They are made up of steel that will not 
 easily become brittle under vibration. 
 
 Lubrication. In most cases the spring eyes are bushed with 
 phosphor-bronze or steel and shackle bolts are hardened and 
 ground. The object of the bushing, of course, is to provide some 
 means to renew the wearing surface. The bolts are working con- 
 
 Rear Spring and Shackle Assembly. Front Spring and Shackle Assembly. 
 
 FIG. 224. Wick Oiling System on the La France 2-Ton Truck Spring 
 
 Shackles. 
 
 tinuously and will wear out quickly if they are allowed to remain 
 dry. This lubrication is effected by grease cups which communi- 
 cate with a hole in the bolt that permits the lubricant to reach 
 the wearing surface. 
 
 In order to simplify maintenance some makers provide a wick 
 oiling system for the spring shackles as illustrated in Fig. 224. 
 This particular illustration depicts the La France construction, 
 while the Fageol and Military class B vehicles are also provided 
 with similar wick oiling systems. On the rear spring shackles 
 oil reservoirs are cast integral with the shackles and wicks are in- 
 serted through drilled holes which feed the oil to the various 
 bearings by capillary attraction. On the front springs the frame 
 bracket carries the reservoir and a wick feeds oil to the upper 
 pin which is hollow, thus permitting the oil to flow by gravity to 
 the lower shackle pin or bolt. 
 
SPKINGS AND SPEING SUSPENSIONS 243 
 
 Although friction between the spring leaves is desirable to an 
 extent, yet it is necessary to keep the leaves lubricated when they 
 bear against one another. This provision is usually made by the 
 spring maker, and in most cases it is necessary to pry the leaves 
 apart and introduce the lubricant with a knife. 
 
CHAPTER XVIII 
 
 THE FUEL SUPPLY SYSTEM 
 
 THE function of the fuel supply system of a commercial car 
 is to furnish the carburetor with an unfailing supply of gasoline 
 until the supply carried is entirely exhausted. This must be done 
 independently of the grades encountered by the vehicle. The 
 gasoline is generally fed by gravity from the tank to the car- 
 buretor, although one maker uses pressure feed, while several 
 others use the vacuum system, which has been so successful on 
 pleasure vehicles. 
 
 In the gravity system the "head" of fuel is depended upon 
 to feed it to the carburetor. Tank location therefore is an im- 
 portant phase of this system, and requires the tank to be elevated 
 above the carburetor. With this system the tank may either be 
 placed on the dashboard or under the driver's seat. In a pres- 
 sure feed system the tank may be located at any level with ref- 
 erence to the carburetor, since the fuel is always under a prede- 
 termined pressure sufficient to maintain a constant level in the 
 carburetor float chamber. This pressure may either be obtained 
 from the exhaust or by a special air pump. 
 
 In the vacuum system the suction of the engine is used to 
 draw gasoline from the supply tank to an auxiliary tank, from 
 which the gasoline flows by gravity to the carburetor. 
 
 Gasoline Tanks. Gasoline tanks are generally made from 
 tinned sheet steel, known as terne plate, and may either be pressed 
 or formed to shape with ends and joints soldered or riveted and 
 soldered. In order to provide the maximum mileage for a vehicle, 
 they must be made to hold from twenty to thirty gallons and 
 must be reinforced, so that the ends are protected from being 
 forced out as the fuel rushes from one end to the other. These 
 reinforcements or baffle plates also serve to prevent rattling due 
 to vibration and sagging at the center of the tank. They are 
 provided with holes or openings so that the gasoline can find a 
 level in all compartments. 
 
 The filler cap and outlet are usually provided with strainers 
 which are made from metal gauze, while shut-off cocks are pro- 
 vided in the outlet to shut off the supply. Some makers also 
 
 244 
 
THE FUEL SUPPLY SYSTEM 
 
 245 
 
 provide a reserve supply in the tank. This is usually accom- 
 plished by a three-way cock fitted with a stand pipe which 
 projects several inches above the bottom of the tank. Ordinarily 
 the gasoline passes through this stand pipe, but when the lock 
 
 FIG. 225. Nash Quad Gasolene Tank and Gravity Feed System. 
 
 is turned to the reverse position, the fuel is permitted to pass 
 through another opening flush with the bottom of the tank. 
 These features are shown in the following illustrations. 
 
 Nash Quad. Fig. 225 illustrates the Nash Quad gasoline tank 
 and the feed pipe and carburetor. This also serves to illustrate 
 the conventional gravity feed system. The filler cap is located 
 
 /HANDLE. 
 
 HAfJDLE^ 
 FILLER CAP^ 
 
 
 
 \5TRAIN E.R 
 
 
 -BAFFLE PLA TE 
 
 
 STRAINER 
 
 
 
 3 
 
 
 ^,,+ert* ;t 
 
 SEATSUPPOPT 
 
 
 
 
 
 1 00 
 
 
 |o 
 
 rfv, 
 
 FRAME 1 
 
 1 
 
 {^^> -* 
 
 
 fr\ U 
 
 f 
 
 O Oj 
 
 FIG. 226. Riker Gasolene Tank and Mounting. 
 
 near the center of the tank and is provided with a large handle 
 so that it can easily be removed. A large strainer fits inside of 
 the filler flange, which is riveted and soldered to the tank. The 
 body of the tank is of rectangular shape and formed from a sheet' 
 
246 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 of steel. The head is set in lapped and soldered as shown in the 
 small sectional view. Two outlets with shut-off cocks are pro- 
 vided, so that gasoline may flow from either or both ends. Each 
 of these cocks are provided with two openings level with the 
 bottom of the tank for the reserve supply, while the regular 
 supply is taken through the stand pipes. 
 
 Fig. 226 shows the Eiker tank and mounting. This tank is 
 of the bolster type, or modified rectangular shape and provided 
 with two baffle plates for reinforcements. The heads are dished 
 outward and the edges of the body are flanged over them and 
 soldered. Both filler and outlet are provided with strainers, and 
 two handles are soldered to the top of the tank so that it can 
 easily be removed for repairs. The upper views show the method 
 of mounting the tank in a steel compartment which supports the 
 driver's seat. This compartment is made of sheet steel and a 
 framework of small angles riveted together. Angles on the front 
 and rear near the bottom support brackets which carry the tank. 
 A strip .of felt is placed between the brackets and the tank to 
 form a cushion and steel straps hold the tank in position. 
 
 SEAT SUPPORT 
 
 FILLER CAP 
 
 FOOT BOARD SUPPORT 
 
 -FRAME CROSS MEMBER 
 
 FIG. 227. Peerless Gasolene Tank Support. 
 
 Peerless and Fierce-Arrow. Fig. 227 depicts the Peerless 
 mounting. However, this differs from the above in that the 
 tank, which is of cylindrical form, is supported and retained by 
 steel straps. It is carried in a steel compartment supporting the 
 driver's seat. 
 
 The Pierce tank is of rectangular shape and supported from 
 the frame by means of sheet steel brackets and wood blocks as 
 
THE FUEL SUPPLY SYSTEM 
 
 247 
 
 shown in Fig. 228. This mounting is so constructed that the 
 framework which supports the seat surrounds the tank. A re- 
 
 WOOD 
 BLOCK 
 
 ^T 
 
 
 _Q_ 
 
 STEEL STRAP 
 
 PRIMING PUMP 
 
 FIG. 228. Fierce-Arrow Gasolene Tank and Mounting. 
 
 serve compartment is provided and arranged, accessible through 
 a handle outside of the seat compartment. Gasoline feed to the 
 carburetor is by gravity and a connection is also made for prim- 
 ing the engine in cold weather. A hand-operated priming pump 
 
 STEEL PLATE- 
 FIG. 229. Kelley-Springfield Gasolene Tank Mounting. 
 
 is attached to the seat compartment and supplies a small quan- 
 tity of gasoline to the motor through the intake manifold. 
 
 On the Kelly trucks the seat compartment is also made of 
 
248 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 wood and the rectangular-shaped gasoline tank fits snugly in 
 this. It is supported by wood beams at each end and at the cen- 
 ter. The tank is placed well above the carburetor to provide the 
 proper^ head as shown in Fig. 229. It is retained by wood strips 
 and protected from excessive heat by a steel plate at the bottom, 
 which provides an air space under the tanks. 
 
 I 
 Stewart and ; Autocar. The Stewart tank (Fig. 230) is 
 
 mounted in a wood seat frame. However, steel straps are at- 
 tached to the tank and form brackets which rest on wood sills. 
 
 
 
 
 
 1 1 
 
 TANK 
 <- STEEL STRAPS-^ 
 
 = 
 
 
 FIG. 230. Stewart Gasolene Tank and Mounting. 
 
 The Autocar tank (Fig. 231) is formed from a sheet but the 
 ends do not lap, as, a pressed cover is used. The heads are also 
 pressed and set into the body. This construction permits riveting 
 and soldering the head and all parts, while the cover which re- 
 ceives very little strain is soldered. This tank is mounted on 
 steel brackets riveted to the frame and is retained by two rods 
 which are supported by two brackets riveted and soldered to the 
 tank. 
 
 Several makers use tanks which are drawn from one sheet of 
 metal and have but one soldered joint. This type of tank is illus- 
 trated in Fig. 232, which illustrates the mounting of the United 
 States trucks. These tanks are tinned inside and out and the 
 bead, is soldered as shown. 
 
THE FUEL SUPPLY SYSTEM 
 
 249 
 
 The United States mounting consists of a separate frame or 
 cradle, very rigid, having two brackets which rest on the vehicle 
 frame, connected by a steel channel and a tie rod. Raybestos is 
 riveted to the brackets to give a cushion effect, and the tank is 
 retained by two steel straps. Gasoline feed is by gravity through 
 
 FILLER- 
 
 
 -r 
 
 RETAINING ffOD [^ 
 AND BRACKETS I 
 
 1 
 
 1 
 
 
 
 C 
 
 RIVET " 
 
 Q 
 
 IT 
 
 OUTLET 
 
 FIG. 231. Autocar Tank with Riveted and Soldered Ends. 
 
 a strainer attached to the tank and supported from the tank 
 mounting. 
 
 Gasoline tanks when soldered and placed under the seat, have 
 given some trouble due to leaks, as in some cases it is quite dif- 
 ficult to hold the tank in such a way as to prevent vibration from 
 
 FIG. 232. U. S. Pressed Steel Tank and Mounting. 
 
 cracking the solder at the joints. The gasoline supply pipe also 
 has its disadvantages since when the motor is placed under a 
 hood, this pipe becomes quite long and it is difficult to keep it 
 free from leaks. 
 
 In order to overcome these objections these tanks on the Denby 
 and Union trucks are mounted on the dash, the Union mounting 
 
250 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 is illustrated in Fig. 233. This position provides the shortest gaso- 
 line line, reducing the dan- 
 ger of leaks due to vibration, 
 while it also provides an 
 ample head of fuel for grav- 
 ity feed. This tank is sup- 
 ported by brackets and 
 straps and is provided with 
 a strainer and shut-off valve. 
 In the pressure feed sys- 
 tem either the pressure of 
 the exhaust gases or air 
 pressure from a mechanical 
 driven pump is used to 
 force the gasoline to the car- 
 buretor float chamber. This 
 system requires consider- 
 able piping, a pressure gage, 
 a pressure regulator or 
 
 TIG. 233. Union Tank Mounting. 
 
 Stewart Vacuum Feed. 
 
 The Stewart vacuum 
 feed is used on the Knox 
 tractor, Kissel Kar trucks 
 and others and is shown 
 in Fig. 234. The mechan- 
 ism is contained in a cy- 
 lindrical tank which may 
 either be mounted on the 
 engine or on the dash- 
 board. The tank is di- 
 vided into two chambers, 
 the upper one being the 
 filling chamber and lower 
 the emptying chamber. 
 The former contains a 
 float valve and the con- 
 nections to the intake 
 manifold and the main 
 fuel tank. The low T er 
 chamber has a connection 
 leading to the carburetor. 
 
 pump and a hand pump. 
 
 CONMCTtON TO 
 GA&QLN TANK 
 
 CONNECTION TO 
 CARBURETOR 
 
 FIG. 234. Stewart Vacuum Tank. 
 
 This lower chamber is always under 
 
 atmospheric pressures as the flow of gasoline from it is by gravity 
 
THE FUEL SUPPLY SYSTEM 
 
 251 
 
 SAFETY VALVE 
 ADJUSTING SCftfW 
 
 SAFETY VALVt 
 
 SIEVE 
 
 PIPE TO 
 GASOLINE TANK 
 
 only. Atmospheric pressure is maintained by an air vent which 
 communicates with the chamber. The suction of the piston on 
 the intake stroke creates a vacuum in the upper chamber, which 
 closes a valve between the two chambers and in turn draws gaso- 
 line from the main tank. The gasoline, as it is being sucked into 
 the upper chamber operates a float valve. When this float valve 
 has risen to a certain mark, it automatically shuts off the suction 
 valve and opens an air valve. This open air valve creates an 
 atmospheric condition in the upper chamber and gasoline imme- 
 diately commences to flow to the emptying chamber. When the 
 float is at the bottom of its 
 chamber, the suction valve 
 is open and the air valve 
 is closed. The lower 
 chamber has a flap valve 
 which prevents the gaso- 
 line in the lower chamber 
 from being sucked into 
 the upper chamber, as the 
 float falls and opens the 
 suction valve. 
 
 On the Knox Tractor the 
 gasoline tank is mounted 
 on the running board and 
 the engine suction through 
 the system described 
 above draws gasoline from 
 the main tank and sup- 
 plies the carburetor. 
 
 Saurer Gasoline Feed System. The Saurer truck uses a pres- 
 sure feed, the gasoline tank being located under the driver's seat 
 and above the level of the carburetor when the tank is full. On 
 the special Saurer carburetor, however, it was found that a con- 
 stant pressure was essential to its proper functioning and the 
 gasoline tank was moved from the rear of the truck to the driver's 
 seat. Fig. 235 is a cross-section of the exhaust pressure device. 
 
 The exhaust gas enters and passes through a screen to remove 
 carbon and fire, any small particles falling to the bottom of the 
 long tube which can be removed for cleaning. The gas then 
 passes to the other chamber through the valve which it lifts. 
 The valve is returned to its seat by a spring to retain the pres- 
 sure in this chamber and prevent its escape back into the exhaust 
 
 AND SED/HENT 
 COLLECT HEft 
 
 FIG. 235. Saurer Pressure Device. 
 
252 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 manifold in the interval between exhausts. The upper valve is a 
 sort of safety valve to prevent the pressure from becoming too 
 great. This valve is regulated by the knurled screw on top of 
 the device. The pressure is maintained at about two pounds. 
 
 Advantages and Disadvantages. Each system has its advan- 
 tages and its disadvantages. Gravity is an absolutely depend- 
 able and constant force which acts independently of an artificially 
 created condition, and can be implicitly relied upon to cause the 
 flow of fuel to the carburetor so long as the pipe is unobstructed 
 and the upper surface of the fuel supply is at a higher level than 
 the gasoline level in the carburetor float chamber. It is the most 
 simple system on account of the simplicity of piping and fittings 
 and there is practically nothing to keep in order. 
 
 The chief disadvantage is that the pressure under which the 
 fuel is supplied to the carburetor is variable. Not only does it 
 diminish progressively as the fuel level in the tank falls, on ac- 
 count of the reduction of the gravity head acting, but it also 
 diminishes whenever that portion of the vehicle which carries the 
 tank stands at a lower level than that which supports the car- 
 buretor. 
 
 With a forced system, as long as the artificial pressure is 
 maintained, there is almost a certainty that gasoline will con- 
 stantly be fed to the carburetor entirely independent of every 
 other conditions. 
 
 The system possesses disadvantages in that there are numerous 
 pipes and joints which must be kept tight in order that the tank 
 may hold its pressure and the multiplicity of pipes and fittings 
 adds to the possibility of leaks due to vibration. 
 
 The vacuum system is by far more simple than the forced 
 system and eliminates the pressure pump, gages, regulator, a num- 
 ber of fittings and an air-tight tank. Leaks in pipes are ma- 
 terially reduced as the pressure is very low. Like the forced 
 system it will supply gasoline to the carburetor regardless of 
 grade, vehicle position or head of gasoline in the main tank. 
 
 This vacuum tank must not be installed in the exhaust side of 
 the engine, as gasoline may leak or overflow from the tank and 
 cause explosions or fires. Proper operation of the system depends 
 entirely upon the float valve and if it develops a leak it cannot 
 shut of! the suction valve as it becomes too heavy to rise. Par- 
 ticles of dirt may also cause trouble by holding the flap valve 
 open, which will render the system inoperative. The piping is 
 also subject to the danger of vibration. 
 
CHAPTER XIX 
 
 CONTEOLS 
 
 THE controls of a commercial car consist of the following: 
 the spark, throttle, clutch, change gear lever, brakes and the steer- 
 ing gear. 
 
 The most important controls are the spark and throttle. The 
 former may either be hand operated from the steering wheel, it 
 may be so arranged as to cause ignition to occur at a predeter- 
 mined point or it may be automatically controlled by the engine 
 speed. The throttle may either be controlled by the driver or 
 automatically. There are two means of manual control, by hand 
 or foot. Automatic control was described in the chapter on 
 governors. 
 
 The conventional type of control for cars with sliding gear 
 transmissions, comprises two pedals located on opposite sides of 
 the steering posts, the one at the left being the clutch pedal and 
 the one at the right the brake pedal. The foot throttle or ac- 
 celerator, if one is provided, is placed either between or to the 
 right of these pedals for operation with the right foot. The 
 mounting of these pedals depends upon the general construction 
 of the vehicle. When a unit power plant is used they are gen- 
 erally mounted on the clutch housing; if the transmission is 
 mounted amidships the common plan is to provide a tubular 
 shaft extending partly or entirely across the frame, which is car- 
 ried in brackets secured to the frame. Formerly the steering 
 column was nearly always placed on the right side of the car, 
 and the hand levers for operating the sliding gears and the emer- 
 gency brake were located just outside of the driver's seat on the 
 right. However, during the past years, quite a few makers have 
 resorted to the left-side drive in which the steering column is 
 located on the left side and the levers either on the left side or in 
 the center. 
 
 On several makes of vehicles the clutch and service brake are 
 operated by a single pedal. The first motion of the pedal re- 
 leases the clutch and a continued motion applies to service brake. 
 The emergency brake may also be operated by a pedal ; however, 
 it must be provided with a ratchet lock. The brakes and clutch 
 
 253 
 
254 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 may also be connected through suitable linkage so that when 
 either brake is applied the clutch will also be disengaged. The 
 idea which led to this construction undoubtedly was that if the 
 driver wants to stop quickly he should simultaneously disengage 
 the clutch and apply the brake, so that the driving effort ceases 
 and no braking effort need be expended in dissipating the energy 
 stored in the flywheel. 
 
 In order to prevent shifting of the gears while the clutch is 
 engaged, some designers have provided an interlock between the 
 gear sliding and clutch mechanism. This is generally so ar- 
 ranged that the gears cannot be shifted unless the clutch is out, 
 and the clutch cannot engage unless the gears are in full mesh. 
 
 The advantages and disadvantages of the two control posi- 
 tions may be divided into general and mechanical. The advan- 
 tages of one are, moreover, usually the disadvantages and advan- 
 tages of the other, so the question may be discussed for one only. 
 The two essential features of the left side control are: first, 
 greater ease in getting out of the vehicle on the right side, and 
 second, the bringing of drivers meeting vehicles next to each 
 other, lessening the dangers of collision. 
 
 The first is of importance only as regards convenience of both 
 operator and helper. The second point is well worthy of con- 
 sideration, as when two vehicles meet on narrow streets or roads, 
 the distance between the two must be judged with great nicety 
 in order to prevent scraping mud guards or bodies and locking 
 wheels. The disadvantages are the difficutly of judging the dis- 
 tance from the curb, the distance of an overtaken vehicle and in 
 some cases the difficulty in mounting the control levers. 
 
 The first claim seems to be a difference of opinion, as there are 
 some who claim one is no more difficult than the other. However, 
 if the distance is not judged properly the tires will suffer, not 
 mentioning the strain imposed on the wheels, axles and steering 
 knuckles in striking curbs. 
 
 In overtaking vehicles the driver is on the left side, and 
 farthest from the overtaken vehicle, and this would seem to be 
 offset by the advantage of bringing the operators of meeting 
 vehicles next to each other, but a close study seems to point in 
 favor of the right side control, for in the case of meeting vehicles 
 two operators are watching and able to judge distance, while in 
 overtaking vehicles there is only one who can judge the distance. 
 
 The mechanical points relate to details of design and apply 
 to each type; however, the center control offers an advantage in 
 
CONTROLS 255 
 
 that the gear lever can be mounted directly on the transmission, 
 thus doing away with superfluous connections. 
 
 Spark and Throttle Controls. Various types of these controls 
 were illustraed in Chapter XIV, describing the steering gear. 
 The general practice is to incorporate these in the steering gear, 
 while the foot throttle or accelerator consists of a small pedal 
 mounted on the dash or foot board and connected with the hand 
 throttle in such manner 
 that it can be operated 
 without changing the posi- 
 tion of the throttle lever on 
 the wheel. This is accom- 
 plished by a slip joint, as 
 shown in Fig. 236. The 
 accelerator is hinged to the 
 steering column and con- FIG. 236. Pierce Throttle Control, 
 nected to the carburetor 
 
 throttle lever by a rod which carries a slip joint. This joint has 
 an extension to which the hand throttle is connected. The ac- 
 celerator is normally held in the off position by a coiled spring. 
 
 Another type of accelerator was illustrated in Fig. 176, Chap- 
 ter XIV, showing the Reo steering gear. 
 
 The advantage of the foot throttle is that it permits the 
 operator to control the speed of the engine with his right foot, 
 thus leaving his right hand free to change gears, and the left to 
 steer the vehicle. The advantage of quick gear-shifting is not 
 to be denied, as anything which tends to reduce engine racing, 
 gear clashing, etc., is quite desirable. However, motor trucks 
 operate on solid tires and the floor boards are constantly vibra- 
 ting, and all of the minor shocks which the vehicle springs do 
 not absorb are transmitted to the cab. This vibration makes it 
 quite difficult for the operator to keep his foot steady, as the 
 slightest movement of his foot acts directly upon the throttle. 
 Sudden acceleration is another disadvantage which is to be 
 avoided. The hand throttle of course eliminates this, and it is 
 possible to hold it stationary on the quadrant. Disadvantages of 
 the hand throttle, besides the inconvenience in changing gears, 
 includes the danger of shifting gears without throttling down the 
 engine. 
 
 Brake, Clutch and Gear-shift Controls. There are two gen- 
 eral types of pedals, the straight and the bent type, both of which 
 
256 MOTOK TKUCK DESIGN AND CONSTEUCTION 
 
 are illustrated. These pedals have to pass through the floor 
 boards and their shape is dependent upon the room available. 
 They may either be drop forgings or steel castings, and vary from 
 10 to 16 inches in length, depending upon the required leverage. 
 Brake and change-gear levers are generally drop forged of 
 I-beam section, and in most cases pivot from a common pivot 
 axis. The change-gear lever of selective type change gears moves 
 in an H segment or gate and does not require a latch to hold it in 
 position. However, a lock is sometimes provided to obviate the 
 possibility of accidentally engaging the reverse gear. A latch 
 lever must always be used with a progressive gear control, and 
 the emergency brake lever must also be provided with a latch. 
 There are two general types of selective gear controls Avhich are 
 termed the sliding shaft and swinging lever types. While all 
 controls may be classified under these two heads, there are numer- 
 ous variations in detail. 
 
 Sliding Shaft Control Set. The Pierce five-ton control set 
 (Fig. 237) is of this type and mounted on the right side rail of 
 
 CHANGE GAR 
 
 f/tAHf 
 
 / GAFi SL/O/HG SHAFT 
 
 BAUL LOCH 
 
 FIG. 237. Pierce Selective Type Control. 
 
 the frame, as the controls are arranged for right side drive. 
 This selective gear control comprises a sliding shaft to one end of 
 which the control lever is rigidly secured, and which at its inner 
 
CONTROLS 
 
 257 
 
 end carries a downwardly extending arm which is arranged to 
 engage with a semi-circular slot in one or the other of the sliding 
 shafts of the transmission which carry shifting forks. The slid- 
 ing shafts are provided with ball locks, which help to find the 
 correct mesh, and also prevent shifting of both shafts together. 
 The H plate or quadrant, which guides the lever in shifting to 
 the various speeds, is placed slightly forward of the emergency 
 brake lever and has a lock controlled by thumb latch on the lever 
 
 FIG. 238. Brown-Lipe Center Control Unit for Unit Power Plant 
 Transmissions. 
 
 handle for locking out the reverse gears. The gear shifting 
 mechanism also has a lock which prevents shifting gears until 
 the clutch has been disengaged. This consists of a semi-circular 
 cam or segment keyed to the sliding shaft of the control set and 
 a plunger connected with the clutch pedal, which, while the clutch 
 is engaged rests in holes in the cam surface. To shift gears the 
 clutch must first be disengaged which also disengages the plunger. 
 18 
 
258 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 The emergency lever is of the spoon latch type which releases 
 a lock fitting into the ratchet teeth of the brake quadrant. 
 
 Another type of sliding shaft control is shown in Fig. 238. 
 This is furnished by the Brown Lipe Co. with their transmissions 
 for left side control, and is used on a number of commercial cars. 
 This differs from the one above in that the control lever is hinged 
 to the sliding shaft, and pivots in a rectangular shaped quadrant. 
 Instead of the lever sliding with the shaft, it pivots to either 
 side in the quadrant and moves the shaft in the opposite direction 
 to which the lever is moved. The emergency brake lever has a 
 spoon latch which operates on the conventional ratchet quadrant, 
 and is pivoted from the same center as the gear lever, but its 
 shaft extends to opposite side of the housing, which encloses the 
 entire control. This type of control is intended for unit power 
 plants where the transmission usually is located under the foot 
 boards. 
 
 The Swinging-lever Type. A swinging-lever type of control 
 used on several cars is shown in Fig. 239, and is designed for 
 right-side control and frame mounting. The change gear lever 
 
 SHORT LEVER 
 PROWDED W/TH LUGS 
 
 QUADRANT AM 
 BRACKET 
 
 /VOl 
 6HORT LEVERS 
 
 FIG. 239. Swinging Lever Type of Control. 
 
 is pivoted to a hub which is free to turn on the control shafts. On 
 each side of this lever are short levers which are fastened to con- 
 centric control shafts, each of which extend to the inside of the 
 frame and carry operating arms. These arms are connected to 
 the sliding shafts of the transmission by rods and clevises. The 
 upwardly extending levers are provided with lugs, between which 
 the control lever engages when it is pressed in the direction of 
 
CONTKOLS 
 
 259 
 
 the particular short lever. Some provision must be made for 
 holding the change-gear lever in a natural position, and this is 
 accomplished by the two flat springs fastened to the short levers. 
 When the control lever is moved in one of the slots of the quad- 
 rant it is connected with one of the short levers and turns the 
 shaft to which that lever is secured. 
 
 FIG. 240. Warner Swinging Lever Arranged for Center Control with Right 
 
 Hand Drive. 
 
 Fig. 240 illustrates another type of swinging lever control 
 which was introduced by the Warner Gear Co. for unit power 
 plant mounting. It differs from the above in the method of en- 
 gaging the control lever with the short levers that turn the con- 
 centric shafts. These have small arms hinged to them, which are 
 held in contact with the control lever by spiral springs. The 
 pivoted arms have a lug which engages in a slot in the quadrant 
 and locks each shaft in position. This type of control eliminates 
 the danger of turning both shafts at the same time. It also in- 
 corporates a reverse lock controlled by a thumb latch on the con- 
 trol lever. 
 
 Center control may also be employed with the transmission 
 located amidships or on the jackshaft. An excellent example of 
 this is shown in the United States control, Fig. 241, in which the 
 support for the gasoline tank is used to support the control. 
 
260 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 FIG. 241. United States Center Control Mounting. 
 
 Center Control and Pedal Mounting. On the Flint delivery 
 cars the center control and pedal mounting is incorporated in a 
 single unit supported from the sub frame as shown in Fig. 242. 
 The control set is of the swinging lever type; however, instead 
 of using a quadrant and concentric shafts, the short arms are con- 
 nected with two parallel shafts which are provided with plunger 
 locks. The short levers instead of pivoting from the center of 
 the control lever, slide with the shaft. This construction permits 
 placing the sliding shafts in the transmission directly above the 
 gears, making a direct connection and eliminates the trouble 
 usually experienced with bent connections. 
 
 PARALLEL 
 SHAFTS 
 
 CHANCE 
 
 GEAR 
 
 LEVER 
 
 FIG. 242. Center Control and Pedal Mounting of Flint Delivery Cars. 
 
CONTEOLS 261 
 
 A large bracket extends from one subframe member to the 
 other and has bearings at its rear end to support the control and 
 brake lever, while bearings are provided at the front end of the 
 pedals and their shafts. The service brake connection is made 
 from a small lever cast integral with the brake pedal, while the 
 clutch is connected to the pedal through a yoke and levers, keyed 
 to the shaft. The brake pedal is interconnected with the clutch 
 pedal so that in applying the brake the clutch will also be dis- 
 engaged. 
 
 Fig. 80 depicts a unit power plant transmission with the 
 center control and pedal mountings for left-side drive. The 
 SAvinging control lever instead of being pivoted at its lower end, 
 has the pivot, which is of spherical shape, a short distance from 
 its end and rests on a bracket incorporated with the transmission 
 cover. The end of the lever engages with the shifter forks in the 
 transmission which have lugs that straddle the lever. This 
 makes a very simple control and eliminates a number of parts. 
 The emergency brake lever is mounted at the side of the trans- 
 mission and is also pivoted a short distance from the end. The 
 lower end has a connection for the brake rod and a slot through 
 which the quadrant is inserted. The pedals are mounted on an 
 extension of the clutch disengaging shaft. Both of these are free 
 on the shaft, but the clutch pedal is connected to a sector which 
 permits pedal adjustment to take up the wear of the clutch. 
 
 Progressive Type Control. In the progressive type of trans- 
 mission it is necessary to progress from one speed to another and 
 for this reason it is necessary to provide a control which has a 
 lock for each speed and the neutral position. The Mogul heavy 
 duty trucks are equipped with a progressive type transmission 
 which is built in a unit with the jackshaft, while the operator's 
 seat is placed over the engine. This makes it difficult to arrange 
 a neat control; however, in the Mogul trucks the control levers 
 and pedals are supported from a single bracket. Both gear and 
 brake levers pivot from the same center and are mounted upon 
 concentric shafts. Since a lock is required for both levers, these 
 are equipped with spoon type latches. The pedals also pivot 
 from a center common to both, but this is somewhat below the 
 center of the levers as shown in Fig. 243. 
 
 The position of the control levers also makes it difficult to 
 obtain a direct connection to the sliding shaft in the transmis- 
 sion. In this case it is quite simple as an extra long lever is 
 
262 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 pivoted from the seat support which connects with the control 
 lever near its pivot end, while the other end is connected to the 
 sliding shaft. 
 
 CLUTCH 
 OPERATING 
 iAFT 
 
 CLUTCH PEDAL 
 
 BRAKE 
 EQUALIZERS- 
 
 TROD AND LEVER 
 
 FIG. 243. Mogul Brake, Clutch and Progressive Type Gear Control. 
 
 Brake Linkage. Unless the breaking force applied to the rear 
 wheels is equalized, that is, that brakes on opposite sides produce 
 equal retarding forces, the car has a tendency to skid and brake 
 adjustment is also quite difficult. This necessitates an equalizing 
 device in the brake operating linkage, which will apply an equal 
 retarding effect to the two brakes of each set. This equalizer is 
 dependent upon the general scheme of the linkage and in most 
 cases is of the whiffletree or modified whiffletree type. The brake 
 linkage is dependent upon the general layout of the chassis. 
 
 With the seat mounted over the engine, it is necessary to ar- 
 range this so it will provide maximum accessibility for the en- 
 gine, and Fig. 243 illustrates how this is accomplished with wire 
 cables on the Mogul trucks. Short rods are connected with the 
 brake pedal and lever and carry turnbuckles which are attached 
 to wire cables. These cables pass over pulleys mounted on the 
 seat frame and the clutch disengaging shaft. They connect with 
 a cross shaft, which in turn is connected with equalizers of the 
 whiffletree type. From these equalizers, rods and clevises form 
 the connections to the brake. The clutch connection is made with 
 a rod direct from the pedal to the clutch disengaging shaft which 
 is supported from the subframe. 
 
CONTROLS 
 
 263 
 
 On the Natco trucks (Fig. 244) the engine is mounted under 
 a hood and the linkage consists of rods throughout. 
 
 CLUTCH ANO SEffV/CS 
 PEOAL. 
 
 CLUTCH ft 00 
 
 FIG. 244. Natco Brake Eod and Pedal Arrangement. 
 
 The pedals are supported by a bracket attached to the frame, 
 while a cross shaft is arranged to incorporate an equalizer for 
 each set of brakes. The clutch pedal also operates the service 
 brake, while the brake pedal has a ratchet which locks auto- 
 
 FIG. 245. Peculiar Brake-Rod Equalizer of the U. S. Truck. 
 
 matically and is released by tipping the pedal pad. The brake 
 equalizer is of a modified whiffletree type and is mounted vertical 
 instead of horizontal. 
 
 An equalizer which is a modification of the bevel gear differ- 
 ential, is used on the United States trucks and shown in Fig. 
 
264 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 245, in which the ordinary brake levers which usually form con- 
 nections for the modified form of whiffletree equalizer are re- 
 placed by bevel gear sectors. The lever to which the brake rod is 
 connected has a spindle upon which a bevel pinion is mounted 
 which meshes with the bevel sectors on opposite sides. This 
 pinion is free to rotate upon its spindle and as the brakes are ap- 
 plied it equalizes the pull on the brake rods on opposite sides of 
 the frame in the same way as the differential equalizes the power 
 applied to the rear wheels. 
 
 FIG. 246. Wick Oiling System on the La France 2-Ton Truck Brake Shafts. 
 
 Most brake shafts and their bearings are lubricated grease 
 cups ; however, on the La France trucks the brake shaft assembly 
 (Fig. 246) is lubricated by oil. Both shafts are hollow and the 
 inner one forms the oil reservoir, which will carry sufficient oil 
 to lubrciate the brake levers for a long time. Wicks are led from 
 the central oil reservoir to the various bearings. The oil is put 
 into the reservoir conveniently from the outside of the chassis at 
 the end of the transverse shaft. 
 
CHAPTER XX 
 
 THE MUFFLER 
 
 ALTHOUGH it is not essential that motor trucks operate as 
 quietly as pleasure cars, it is quite essential that they operate 
 without disagreeable noise. For this reason the exhaust must be 
 muffled, which is accomplished by passing the spent gases through 
 a muffler before they are discharged into the atmosphere. This 
 muffler is sometimes referred to as a silencer. The object of the 
 muffler is to permit the gases to expand and to cool, thereby re- 
 ducing the pressure, which is the cause of the noise when they are 
 discharged into the atmosphere directly. It is quite simple to 
 obstruct the passages of the gases from the engine to atmosphere, 
 however, in order to discharge them without disagreeable noise, 
 they must be permitted to escape very freely, so that they will 
 not create any back pressure on the pistons during the exhaust 
 stroke. 
 
 Muffler not Close to Engine. In most cases the muffler is 
 mounted as far away from the engine as the general chassis de- 
 sign permits. It is usually mounted under the frame of the 
 vehicle. This arrangement permits the engine to exhaust into an 
 exhaust pipe of considerable length, the capacity of which is 
 sometimes as much as four times the piston displacement of one 
 cylinder. This long pipe gives the gases a chance to cool before 
 they reach the muffler, while the latter should be arranged in such 
 a manner that heat may rapidly be abstracted from the gases. 
 
 Mufflers generally consist of a series of expansion chambers 
 which communicate by means of fine and sometimes tortuous pas- 
 sages, and after passing through these chambers the gases are 
 finally permitted to escape. Mufflers should possess certain fea- 
 tures, a construction which permits cleaning, strength to with- 
 stand pressures of gasoline air vapor explosions at atmospheric 
 pressure and ability to resist vibration. Cleaning is necessary, as 
 lubricating oil and solid carbon particles held in suspension by 
 the gases will clog the fine passages and increase the back pres- 
 sure. Some mufflers are so constructed that they can be dis- 
 mantled for cleaning. Explosions in the muffler are frequent, and 
 it is essential to have enough strength to resist this pressure with- 
 
 265 
 
266 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 out bursting. The walls of the muffler may be so designed as to 
 prevent ringing which is really a harmonious vibration of suc- 
 ceeding exhausts. This is sometimes accomplished by lining the 
 outer shell with sheet asbestos, but this may not seem very de- 
 sirable, as it possesses certain heat insulating qualities. 
 
 The final outlet is generally through a pipe of considerably 
 less cross section than the exhaust pipe. This is sometimes flat- 
 tened so that the gases escape in a continuous sheet. In some 
 cases this is accomplished by a series of small holes in the final 
 outlet or the outer shell. 
 
 Cut-outs. In order to relieve the so-called back pressure of 
 the muffler, cut-outs are sometimes provided, which are placed 
 forward of the muffler or in the exhaust pipe, and permit ex- 
 hausting the gases directly into the atmosphere, instead of hav- 
 ing them pass through the muffler. The general claim for this 
 cut-out is that it adds to the efficiency and power of the engine. 
 However, it has been proven that with a well designed muffler a 
 cut-out is of little value, except that the operator may occasion- 
 ally listen to the action of the engine. 
 
 Pierce Muffler. The Pierce muffler (Fig. 247) consists of two 
 adjacent cylindrical chambers, which communicate through a 
 number of holes in the inner chamber. The outer chamber is 
 divided into three expansion chambers, while the inner member 
 
 BRACKI r 
 
 CENTRAL TUBE 
 eVHNSK,* CHAMBER / t*- EXPANSION CHAMBER /v expAN3 , w 
 
 -- *- ^f?,- 
 
 , I - \j _ ji ! _ & _JLJL 
 
 FIG. 247. The Pierce Muffler. 
 
 is also divided into three parts, the partitions of each member 
 being pressed steel discs. The gases first enter the inner chamber 
 and pass through perforations into the outer chamber and from 
 this chamber they return to the second portion of the inner cham- 
 ber and thence into the second expansion chamber, thence 
 through the central member into the third expansion chamber 
 and back into the central member from which they are dis- 
 charged. This muffler is mounted parallel to the side members of 
 the frame and has cast end plates which have integral brackets 
 for frame mounting. The tubular members and end plates are 
 
THE MUFFLEE 
 
 267 
 
 held together by long tie rods which extend the full length of 
 the muffler. 
 
 Packard Muffler. The Packard muffler (Fig. 248) also con- 
 sists of an inner and outer chamber with cast end plates, retained 
 
 FIG. 248. The Packard Muffler. 
 
 by tie rods. However, the necessary volume is obtained by in- 
 creasing the diameter instead of making the muffler of consid- 
 erable length. The inner chamber has a series of small holes, 
 through which the gases pass after expanding in the inner cham- 
 ber. After expanding in the outer chamber they escape at the 
 rear end. This outer chamber is insulated with sheet asbestos 
 retained by plates and 
 small screws to deaden the 
 vibration. The support- 
 ing brackets are made of 
 pressed steel and fit into 
 the side members of the 
 
 TCft EXPANSION CHAMBfft 
 
 frame. 
 
 FIG. 249. The Gray-Hawley Muffler. 
 
 Gray-Hawley Muffler. The Gray-Hawley muffler (Fig. 249) 
 is used on a number of commercial cars and consists of two cast 
 heads which support three cylindrical sheet metal tubes. The 
 gases enter the inner one of the three members from the exhaust 
 
 pipe. They expand in 
 this chamber and then 
 pass through fine per- 
 forations at the opposite 
 
 HS/O/V CHAMBERS 
 
 FIG. 250. The U. S. Muffler with Cutout. end in the Partition wall 
 
 into the intermediate 
 
 chamber, and thence through similar perforations at the rear end 
 of the innermost portion wall into the outer chamber from which 
 they escape at the further end. The path of the gases is shown 
 by the arrow-heads in this illustration. 
 
 United States Muffler. The United States trucks are equipped 
 with the muffler shown in Fig. 250 which is similar to the one 
 
268 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 previously mentioned. The gases take the same path and are ex- 
 panded in a similar manner. However, they are discharged 
 through perforations at the center of the outer chamber, as this 
 muffler is mounted crosswise at the rear end of the subframe. 
 Into the head, which connects with the exhaust pipe, a cut-out is 
 placed. This cut-out consists of a poppet valve, held to its seat 
 by a spring and bell crank pivoting in a bracket operated through 
 suitable linkage from the operator's seat. When this cut-out is 
 opened by raising the valve from its seat, the greater part of the 
 gases take the path of the least resistance, which is through the 
 valve opening instead of passing through the various expansion 
 chambers. 
 
 Riker Muffler. The Riker muffler (Fig. 251) is somewhat 
 similar to those depicted above, except that the inner chamber is 
 perforated at both ends and the outlet is of a different shape. 
 Both end plates or heads are provided with flat surfaces to which 
 
 the supporting brackets 
 are bolted. The front head 
 has an opening against 
 which a flat valve is held 
 through the pressure ex- 
 erted by a coiled spring at- 
 tached to the end of a bell 
 
 crank and the head. The bell crank supports the valve, which is 
 raised from its seat when the cut-out pedal is depressed. Both 
 exhaust and outlet pipes are attached to the muffler heads by 
 flanges and bolts. 
 
 Powell Muffler. The Powell muffler is also used by some 
 makers of commercial vehicles. This consists of a number of 
 pressed steel cups, the open 
 ends of which are flanged 
 out so as to fit over the 
 closed end of the adjacent 
 section or cup. Each of 
 the cups A are perforated 
 
 FIG. 251. Eiker Muffler and Cutout. 
 
 FIG. 252. The Powell Muffler. 
 
 and through these perfor- 
 ations the adjacent cham- 
 bers communicate. Cups 
 B and G are used at the 
 
 rear end and are so arranged as to form a somewhat tortuous 
 passage for the gases. This is accomplished by a series of small 
 
THE MUFFLER 
 
 269 
 
 perforations in cup B while cup C has a large central hole. Three 
 tie rods hold the various sections together, which permits using 
 any number of cups to meet the requirements of each individual 
 engine to which the muffler 
 may be fitted. Fig. 252 
 shows this muffler as ap- 
 plied to the Mogul trucks, 
 and Fig. 253 illustrates its 
 application to the Knox 
 tractor, in which it is 
 mounted crosswise at the 
 front end of the frame. 
 
 FIG. 253. The Knox Tractor Muffler. 
 
 Denby Muffler. A pressed steel muffler has recently been in- 
 troduced by Gueder, Paeschke & Frey Co., which is used on the 
 Denby trucks. This is illustrated in Fig. 254, and consists of a 
 number of pressed steel cups placed in a steel shell and elec- 
 trically welded. This makes a very light construction and the 
 claim is made that it weighs but five pounds. The gases enter at 
 
 -MUFFLER SHELL 
 
 CONICAL CUPS 
 
 FIG. 254. The G. P. & F. Muffler. 
 
 the forward end and pass through conical-shaped cups which 
 are so spaced that an expansion chamber is formed between 
 them. The remaining cups are of similar shape, but reversed in 
 position and also provide limited expansion chambers between 
 them. The first of these is perforated, while the second has but 
 one large central hole, and the third has but half the number of 
 perforations of the first one. The outlet, instead of having one 
 large central opening, is also perforated, so that the gases escape 
 in continuous streams. 
 
 Fig. 255 depicts another popular type of muffler known as the 
 " Dunco," which operates on a principle of automatic adjustment 
 which is that of the well-known steam ejector. A portion of the 
 exhaust gases pass directly through a central tube to a high speed 
 jet, at the outlet of that tube, and induce a partial vacuum be- 
 hind them, thus drawing the remaining gases through baffle 
 plates or cones in the muffler. It is claimed that this muffler is 
 
270 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 self-adjusting to variations in speed, and the frequency of in- 
 jector impulses varies directly as the speed of the engine, so that 
 the pull of the ejector is always proportional to the volume of 
 
 FIG. 255. Bunco Ejector Type Muffler. 
 
 gas to be drawn through and discharged. The heads are mal- 
 leable castings and tie rods hold the entire construction together, 
 so that it is very simple to take the muffler apart for cleaning. 
 
 Maxim Silencer. The Maxim silencer (Fig. 256) incorporates 
 a somewhat different principle in which but one tubular member 
 
 is used. The interior con- 
 struction is of a peculiar 
 built spiral chamber, which, 
 it is claimed, can not 
 clog or collect carbon. The 
 gases enter at one end and 
 pass from inlet to outlet 
 without obstructions of 
 any kind. This contin- 
 uous channel has the pecul- 
 iarity of circular or helical form, and, owing to the centrifugal 
 force of the fast moving gases, these gases whirl to the outer 
 periphery, traveling an approximate distance of three and one- 
 half times the length of the muffler. Slow moving gases will re- 
 main at the center and grad- 
 ually move forward to the 
 outlet. The heads are mal- 
 leable, while the shell is 
 made of sheet steel, seamed 
 and electrically welded to FIG. 257. The Old Berg Muffler. 
 prevent bursting. 
 
 Oldberg Muffler. The Oldberg muffler (Fig. 257) has a series 
 of expansion chambers. The gases enter the center member and, 
 due to the arrangement of the perforations, immediately start 
 
 FIG. 256. The Maxim Silencer. 
 
THE MUFFLER 
 
 271 
 
 to pass out and around to the opposite side. Each alternate tube 
 is placed eccentrically with respect to the axis of the muffler. 
 The perforations in each tubular member are arranged in two 
 rows throughout their length. The total area of these perfora- 
 tions is greatly in excess of the area of the exhaust pipe con- 
 necting with the muffler. The sound waves are interrupted by 
 passing half of the gases around each side of the tubular mem- 
 bers, the two streams coming together on the opposite side of the 
 preceding chamber. 
 
 FRAME SIDE MEMBER 
 
 HEAD WITH 
 '/NTFfEOAL BRACKET 
 
 EXPANSION CHAMBER 
 
 / 
 
 CENTRAL TUBE 
 
 OUTLET 
 eXHAUST PIPE 
 
 PACK/NG 
 'LAMP NUT 
 
 FIG. 258. The I. H. C. Muffler for Two-Cylinder Opposed Motor. 
 
 The mufflers described above apply to four and six cylinder 
 engines, while Fig. 258 illustrates the I.H.C. construction for 
 their two-cylinder engines. It consists of an inner and outer 
 shell with cast heads retained by a single tie rod. The gases 
 enter the outer chamber near its center through exhaust pipes 
 from each cylinder. They expand in this outer chamber and pass 
 through perforations in the walls of the inner member, whence 
 they escape at both ends, as the muffler is mounted crosswise at 
 the rear end of the frame. The outlets and mounting brackets 
 are cast integral with the muffler heads. The end view illustrates 
 the method of retaining the exhaust pipes with packing joints. 
 
 The exhaust system begins with the exhaust manifold of the 
 engine and includes the exhaust pipe, cut-out and muffler. Prac- 
 tice differs with the various makers however. What has been 
 outlined in this and previous chapters on the engine serves to 
 give a general idea of the subject. 
 
CHAPTER XXI 
 
 MOTOR TRUCK WHEELS 
 
 ROAD shocks must first be taken by the road wheels, through 
 tire contact, and thence distributed, spreading out in all direc- 
 tions from the hubs of the wheels. 
 
 There are essentially three types of wheels used on motor 
 trucks at present: wood wheels of the artillery type which are 
 used on a great number of machines, pressed steel and cast steel 
 wheels. 
 
 Artillery Wood Wheels. The artillery type of wheel consists 
 of a set of spokes turned from very tough wood, generally sec- 
 ond growth hickory, which are clamped at their inner end be- 
 tween flanges on a metal hub and at their outer end tenoned into 
 a wooden felloe, which is surrounded by a steel band or ring. 
 The spokes may be either of elliptic, square or rectangular sec- 
 tion, and great care is taken to get the fiber to run exactly in the 
 direction of the spoke length. It is common practice to split the 
 spoke billets instead of sawing them. 
 
 The wood used in the spokes and felloes is made from well- 
 seasoned timber, so that strength and toughness in the highest 
 degree can be obtained. Second growth stock and stock from the 
 lower portion of small trees yields the best parts. 
 
 In truck work when solid tires are used the spokes are of 
 square or rectangular section, since these are stronger in propor- 
 tion to weight than the elliptic spoke. 
 
 The greatest amount of trouble with the artillery wheel has 
 been experienced with those used on very heavy trucks. The 
 spokes are very thick and a comparatively slight shrinkage of 
 the spoke causes them to loosen in their hub and the severe jar- 
 ring, due to the use of solid tires, then has a very destructive 
 action. In order to deviate this difficulty and strengthen the 
 spokes assembly at the center the Schwartz Wheel Co. make the 
 miter of the spokes interlocking, while other makers provide keys 
 between the miters or adjacent spokes. 
 
 Steel Wheels. Cast-steel wheels are now gradually coming 
 into use, while pressed steel wheels are also used on some of the 
 
 272 
 
MOTOR TRUCK WHEELS 
 
 273 
 
 vehicles having less than two tons capacity. The steel wheel is 
 very popular in foreign countries, and American manufacturers 
 are gradually using them. In some cases they have not succeeded, 
 while in others they have given excellent service, which is also 
 true of the wood wheel. 
 
 The advantages possessed by the steel wheel for heavy duty 
 are strength, true shape, rigidity, concentricity of the hub and 
 accurate design for the support of the load. In point of strength 
 and elastic limit, the steel wheel well made, is superior to the 
 
 FIG. 259. Natco Front Wheel. 
 
 wood wheel, and will sustain more in impact and side thrust. 
 Another advantage is that they may be accurately machined and 
 once round, they will stay so regardless of humidity, heat, etc., 
 that affect most wood wheels. In design these wheels may have 
 the brake drum, hub and flange cast integral so that there are no 
 bolts and rivets to loosen or break. Considering weight, for 
 vehicles of three-ton capacity and over, the steel wheel is lighter 
 than a wood wheel of equal strength, while for two-ton vehicles 
 both types are about equal in weight. 
 
 The pressed steel type of wheel for trucks up to two-tons 
 capacity is somewhat lighter in weight than a wooden wheel of 
 corresponding capacity. This tjpe of wheel can be produced for 
 practically the same price as wood wheels, when the complete 
 wheel is considered. 
 
 The steel wheels vary in construction, and opinions differ as 
 to which construction gives the best service. 
 19 
 
274 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 An idea of the construction of wood and steel wheels can be 
 obtained from the illustrations presented herewith and the de- 
 scriptions which follow : 
 
 Fig. 259 illustrates the Natco one-ton front wheel with de- 
 mountable tire. The wheel has twelve square spokes which are 
 turned into the felloe and retained in the hub by twelve bolts 
 placed between adjacent spokes. The general form of the hubs 
 is largely determined by the dimensions of the bearings and their 
 necessary distance apart. One hub flange is generally made in- 
 tegral with the hub casting, while the other is free to be slipped 
 over a machined cylindrical surface so as to be accurately guided. 
 
 FIG. 260. Mogul Wheel Spoke, Felloe and Felloe Band Assembly. 
 
 Fig. 260 depicts the construction of the Mogul six-ton rear 
 wheel which is equipped with 40 X 7 in. S.A.E. tires. There are 
 eight spokes of rectangular section and eight spokes of square 
 section. These are all of the same thickness, but the rectangular 
 ones are used for attaching the brake drum, and practically the 
 same strength as the square spokes, as considerable stock is re- 
 moved by the bolt holes. The hub bolts pass through the miter 
 joints of adjacent spokes as shown. The felloe is made to S.A.E. 
 dimensions, and the S.A.E: felloe band is shrunk over it. 
 
 Cast steel wheels may be either of the spoke or disc type, and 
 both seem to be giving good results. The disc type either have 
 a single or a double disc, depending upon the capacity, while the 
 spoke type may have either tubular or cross-section spokes. 
 
MOTOR TRUCK WHEELS 
 
 275 
 
 The single-disc type is at present being used on the Nash Quad 
 Trucks, and this application is clearly shown in Fig. 261. The 
 essential features of this type of wheel are a cast hollow box sec- 
 
 FIG. 261. Nash Quad Cast-Steel Wheel. 
 
 FIG. 262. Besco Cast Rear Wheel for Dual Tires. 
 
 tion rim supported by a curved spring-like section to struts con- 
 necting with the hub. The disc includes a solid cast brake drum 
 and container for the driving mechanism. The working parts 
 
276 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 of the drive are thoroughly protected from injury by the wheel 
 disc and brake drum. It will be noted that the hub is cast in- 
 tegral and that there are no bolts and nuts to loosen except those 
 which retain the internal gear. 
 
 FIG. 263. Spoke Type Cast-Steel Front Wheel. 
 
 The double-disc type for heavier vehicles is shown in Fig. 
 262. The hub and brake drum are cast integral, while the re- 
 siliency is obtained through a wide curvature of both discs. The 
 rim is also of box-like section, however, the discs extend to the 
 hub instead of forming a strut at the bottom. 
 
 Fig. 263 depicts a spoke type of front wheel with integral 
 hub and rim; There are eight spokes of cross section thoroughly 
 ribbed and fitted to obtain the greatest possible strength with 
 minimum weight. 
 
 Fig. 264 shows this type of rear wheel; however, the spokes 
 are of Y-shape, which affords a greater number of supports to 
 the wheel rim without increasing weight, and enables the driving 
 stresses and road shocks to be more equally distributed over the 
 whole wheel. 
 
 Fig. 265 illustrates the hollow-spoke type of wheel. These 
 spokes are of tubular section and are connected to the rim by 
 large fillets. The hub is cast integral, w r hile the brake drum may 
 be cast integral or bolted to this type of wheel. 
 
 Efforts to decrease the weight of steel wheels for vehicles 
 under two-tons capacity, has led to the building of wheels having 
 the disc and lighter sections of the wheel made of pressed steel, 
 rigidly connected to cast steel hubs. 
 
MOTOR TEUCK WHEELS 
 
 277 
 
 This construction is shown in Fig. 266. The construction is 
 similar to the cast wheel mentioned above with a box type hollow 
 rim, except that the discs are flanged a little deeper at the rim to 
 
 FIG. 264. Spoke Type Cast-Steel Eear Wheel. 
 
 FIG. 265. Hollow-Spoke Type Rear Wheel. 
 
 form a wider box section. The cast flange of the hub is carried 
 out further to carry the brake drum and the driving mechanism. 
 Wheel construction seems to be one of the principal problems 
 on which manufacturers do not agree. The wheels on large capa- 
 city vehicles to-day are called upon to carry a very heavy burden 
 
278 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 at higher speed than ever, and they must also stand the strain due 
 to transmission of power. In order to meet these conditions, the 
 proportions of spokes and felloes have been materially increased, 
 and following the precedent of Europe, cast steel wheels are 
 being considered. 
 
 FIG. 266. Pressed Steel Eear Wheel for Internal Gear Drive. 
 
 Some advantages of the cast wheel have been outlined above, 
 while of course it possesses certain disadvantages. However, the 
 steel wheel can not be altered for different types and sizes of 
 tires as easily as a wood wheel and a spoke in a wooden wheel, if 
 broken can be replaced; but in this event the entire steel wheel 
 would have to be replaced. Castings are always liable to flaws 
 and blow holes and it is difficult to secure homogeneous metal 
 free from hard spots. Unequal sections cause local variations 
 in strength and internal stresses due to shrinkage in moulding. 
 Where numerous cores are used in moulding, it is difficult to 
 anchor these so that a uniform thickness of metal can be ob- 
 tained. Strains due to shrinkage can be eliminated to some ex- 
 tent by heat treating. The principal argument against this 
 wheel is that under severe service it crystallizes; however, the 
 design of this type of wheel is of such nature that this so-called 
 difficulty has never existed. 
 
 A steel wheel is made in one piece and can be arranged to 
 have an integral brake drum, hub and flange, and there is no op- 
 portunity for any working of the various joints. The very 
 nature of this type of wheel adapts it wonderfully to the trans- 
 
MOTOR TRUCK WHEELS 279 
 
 mission of power, as the strength lies in the very points where 
 the driving strains are centered. 
 
 The absolute concentricity of the hub, sprocket and flange 
 assist greatly in the economical and efficient transmission of 
 power, for with no high and low spots, there is no alternate 
 tightening and loosening of the chain. In shaft-driven vehicles 
 this condition is even more important. 
 
 Steel wheels also possess considerable advantage in carrying 
 dual tires. In the case of off- set felloes, the outer tire is entirely 
 unsupported by the spokes; however, in this case the steel wheel 
 is particularly valuable, as the felloe can be so designed that the 
 strains on the outer part can be successively transmitted to the 
 spokes or discs without any danger to the wheel itself. Another 
 feature is the decreased weight at the rim which permits more 
 rapid acceleration. 
 
 The advantage of obtaining wheels all assembled and com- 
 plete for mounting is considerable. No division of responsibility 
 exists as to the mounting of wheels on hubs, brake downs, etc. 
 
 Cast steel or pressed steel wheels can be and are made to-day 
 at figures competitive with wood wheels. If the demand in- 
 creases and they are ordered in large quantities, the cost will de- 
 crease. In considering cost it should be remembered that the 
 steel wheel has the hub integral, and the rear wheel may also 
 have the brake drum integral and the cost of these together with 
 all bolts, nuts, felloe band and the labor of fitting them must be 
 added to the wood wheel to get a comparison in price. 
 
 From present indications it appears as though the steel wheel 
 will shortly replace the wood wheel on at least the heavy vehicles. 
 The demand is continually increasing, and quite a number of 
 commercial car builders are experimenting with steel wheels. 
 
CHAPTER XXII 
 
 MOTOR TRUCK TIRES AND RIMS 
 
 IN the previous chapters considerable has been mentioned 
 about tires and their functions. However, in this chapter the con- 
 struction of a motor truck tire and its mounting on the felloe 
 band of the wheel will be described. To be absolutely efficient, a 
 commercial car must be able to carry its load whenever and 
 wherever needed. The vehicle itself may be as nearly as possible 
 absolutely efficient, when measured by this standard, but as a 
 whole it can be no more efficient than its weakest part. Each part 
 must be so designed and so co-ordinated with other parts as to 
 perform in the most efficient manner. In this respect the tires 
 are no exception. 
 
 The functions which the tires perform, reduced to their sim- 
 plest terms, may be listed as follows: (1) To give traction to the 
 wheels and prevent slipping, (2) to protect the mechanism of the 
 vehicle from jars and vibrations, (3) to cushion the load. 
 
 Tire Development. Before the advent of the motor truck, 
 solid rubber tires were used almost exclusively on the wheels of 
 carriages to provide easier riding. On these vehicles the wheels 
 were merely rolling members and performed no tractive effort, as 
 the horses did the pulling. Such tires were held in place by 
 means of wires embedded circumferentially in rubber, the whole 
 unit being mounted on a steel channel shrunk on the felloe of the 
 wheel. These tires were easily applied, but possessed certain dis- 
 advantages such as slipping in the channel, cutting at the base 
 and release of the rubber adjacent to the wires. 
 
 This type of tire did not prove very satisfactory for heavy 
 vehicles, for the reasons mentioned above. In order to overcome 
 these shortcomings, a new tire was introduced, which was called 
 the side-wire' type. In general shape and appearance it was the 
 same as the earlier type. However, it was retained in the chan- 
 nel by means of short cross wires embedded in the base of the tire, 
 which projected on either side. These cross wires were held in 
 place as securely as possible by two other wires running circum- 
 ferentially around the base just inside the edges of the channel. 
 
 280 
 
MOTOR TRUCK TIRES AND RIMS 281 
 
 With the introduction of the commercial car, an entirely new 
 and different function was required of the tires, that of trans- 
 mitting the driving power from the rim of the wheel to the road 
 surface, i.e., the tires became part of a tractive rather than a 
 rolling member. Their carrying capacity was also increased 
 because the gasoline engine could move heavier loads than the 
 horse, while the weight of the truck itself was considerably more 
 than the wagon, and the speed was also increased considerably. 
 The carriage type of tire was found entirely too light to perform 
 the work required of it. This condition brought about the inven- 
 tion of the solid motor truck tire, a tire vulcanized in circular 
 endless form to fit the dimensions of the wheel. This type of tire 
 has been brought out in different designs and types such as flange, 
 internal wire, side wire, hard rubber and metal-base types, also 
 the demountable. 
 
 Carriage tires were made in oval shape, in cross sections from 
 three-fourths inch and of compound rubber which is formed 
 through a tubing machine die, vulcanized in long moulds with 
 many cavities, in the shape in which it had been designed. 
 
 The construction of solid truck tires that have been put on 
 the market is very similar in a general way. The rubber is 
 forced through a die or tubing machine, or built up from sheets 
 of calendered stock in endless form to fit the exact dimensions of 
 a wheel on a particular style of base or retaining body of the tire 
 as designed by the different manufacturers, according to their 
 ideas, which have taken various forms, such as circumferential 
 and side retaining wires which are engaged over embedded cross 
 wires, bases of hard rubber in various forms also semi-hard 
 rubber which can be moulded into the tire and more recently the 
 metal-base type. 
 
 This tire is built on the rim at the factory and cannot be sep- 
 arated from it. The surface of the metal rim is cut with grooves, 
 under cut notches or in other ways, so that the hard rubber gets 
 a firm anchorage into the rim. In manufacture this rubber base 
 is applied in some factories in layers, just as you wrap a bandage 
 on your finger. The base is relatively thin, perhaps not one- 
 eighth the radial thickness of the tire. On the top of this is built 
 the regular rubber part of the tire, of softer rubber to afford the 
 desired resilience. This part is also in some factories built up 
 similar to wrapping a bandage until the desired thickness is ob- 
 tained, which, when done, the tire is trimmed to shape and vul- 
 canized. 
 
282 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 Two Metal-base Types. This metal-base tire is made in two 
 types, the pressed-on and demountable. In the larger cities, the 
 former is quite popular, whereas, in the smaller outlying cities 
 and towns the demountable type has the following. The reason 
 for this is: To remove a pressed-on tire from a truck wheel or 
 put one on a truck wheel requires a powerful press, which means 
 a considerable outlay to the dealer in proportion to the amount 
 of work he may get. 
 
 The demountable tire can be removed from the wheel and a 
 new one fitted, without the truck owner having to take it to a 
 garage. Unfortunately it is more expensive than the pressed-on 
 tire, due to the forged and rolled steel parts used with it. 
 
 Rubber. Crude rubber is a vegetable product gathered from 
 certain species of tropical trees, shrubs, vines and roots. It was 
 first used for pencil erasers and in waterproof cloth and finally 
 in solution in cements. Vulcanizing or curing rubber was dis- 
 covered in 1844; thereafter the development of the industry was 
 rapid, though it was but an infant in size, compared with now, 
 up to the development of the automobile industry. 
 
 There are many kinds and grades of rubber, and these may be 
 divided into two classes, wild and cultivated. 
 
 Wild Rubber. This is collected from trees that have grown 
 wild and where there has been no cultivation process. Such 
 trees and shrubs are found mostly in Northern South America, 
 Central America and Central Africa. Fine Para comes from 
 the Amazon region of South America. For over a century this 
 rubber has been gathered in practically the same way. The 
 native goes into the forest, selects a tree, cuts V-shaped grooves 
 in herring-bone fashion around the tree, with one main groove 
 down the center like the main vein in a leaf. The latex of the 
 tree (not the sap) flows from the smaller veins and down the 
 center vein into a little cup placed to receive it. 
 
 When full these cups are gathered and brought into the rubber 
 camp, and there the latex is coagulated by means of smoke. 
 This is done by the use of a paddle, which is alternately dipped 
 into a bowl of latex and then revolved in the smoke which seems 
 to have a preservative effect on the rubber as well as drying it 
 out and causing it to harden on the paddle, each successive layer 
 of latex causing the size of the rubber ball or biscuit to increase. 
 When a biscuit of sufficient size has been coagulated it is re- 
 moved from the paddle and is ready for shipment. There are 
 
MOTOE TRUCK TIKES AND RIMS 283 
 
 other grades of rubber which are coagulated by adding some 
 alkaline solution and allowing it to dry out. Central America 
 produces a grade of rubber which is cured by being mixed with 
 juices which are obtained by grinding up a certain plant which 
 grows in that district. 
 
 In Central Africa some of the rubber is gathered from trees, 
 but most of it comes from vines and roots, and the methods of 
 coagulation are varied. Practically all of them are dried out in 
 the sun. 
 
 Cultivated Rubber. Cultivated rubbers are obtained from 
 East India, Ceylon, Malayan Peninsula and southern Mexico. 
 The claim is made that the best of these is the Ceylon rubber, 
 which has been grown from sprouts taken from the wild Para 
 trees of South America. These cultivated trees have been very 
 carefully reared and scientific methods used in tapping them, so 
 as not to in any way hurt the bearing qualities of the tree. This 
 product is very uniform, as very scientific methods are used, 
 coagulating, drying and otherwise treating the rubber before it 
 leaves the plantation, so that there is a minimum deterioration 
 due to oxidation and other actions during the time the rubber is 
 en route from the plantation to the manufacturer. Of late, far 
 east rubber is being given the preference, because it is cleaner 
 and contains less foreign matter than the wild para. 
 
 Manufacturing Process. This rubber as it comes into the 
 market, contains a lot of impurities, and before it can be used it 
 has to be washed. This washing is done between rolls which are 
 grooved to tear the rubber apart, water being fed on the rolls to 
 wash off all foreign matter. In this process the rubber loses 
 considerable of its weight. 
 
 When the rubber is washed and dried it is mixed with chem- 
 icals and into a compound. These chemicals and particles of 
 rubber are placed in metal boxes a couple of feet square. The 
 formula for these compounds are, of course, kept secret by the 
 rubber factories, because they represent the outcome of very long 
 and tedious experiments which are looked upon as one of the 
 chief assets of any rubber mill. These masses of compounds are 
 chewed and rechewed, ground and reground, extenuated and re- 
 extenuated, between the giant steel rolls of the calendering ma- 
 chines that are needed just to thoroughly mix the ingredients. 
 Each compound requires its separate mixing, its special treatment. 
 
284 MOTOE TEUCK DESIGN AND CONSTEUCTION 
 
 The rims to which the hard rubber is vulcanized are in most 
 cases copper plated, as rubber compounds do not take kindly to 
 steel. The hard rubber base is applied to the metal rim and then 
 the tire is completed as previously mentioned. 
 
 The compound rubber is in graduated consistencies from the 
 hard rubber base, which forms the inside circumference next to 
 steel base, to the resilient rubber forming the wearing part of 
 the tire. 
 
 When the tire is completed it is pressed into moulds which 
 are securely bolted and placed in large cylindrical vulcanizers 
 which vulcanize or cure the rubber. When this process has been 
 completed and the tires have cooled, slight edges remain which 
 are buffed off. 
 
 Rims. Tire rims or metal bases and felloe bands are usually 
 made from flat stock and rolled to shape, and the ends are 
 welded together. Special machinery is used for this purpose and 
 each band or base must check within certain limits. Demount- 
 able rim parts are made in a similar manner and must also be 
 held within certain limits. 
 
 The Solid-truck Tire. A number of illustrations are shown 
 herewith, which give the contour and general construction of the 
 solid tire. The Firestone wired-on tire is made and recommended 
 for use on light vehicles only. This tire is not manufactured 
 into the rirn as is the hard rubber base type, but is afterwards 
 
 attached to the rim. Into 
 
 CROSS WIRE placed stout cross wires at 
 -FLANGE frequent intervals. When 
 -BOL T this tire is placed on a chan- 
 
 FELLOE BAND nel rim it is held in place by 
 FELLOE two circumferential wires, 
 
 FIG. 267. Eepublic Side-Flange Type Tire, one at each side of the tire, 
 
 these wires resting upon 
 
 the ends of cross wires, by virtue of which the tire is retained on 
 the rim. Swinehart manufactures what is called a soft-base tire, 
 with cross wires for holding it in the channel rim. Several other 
 makers also manufacture tires which are retained by cross or cir- 
 cumferential wires. 
 
 The hard rubber base tire as previously mentioned is built 
 onto the rim at the tire factory. This type of tire is being made 
 by Goodrich, Firestone, Goodyear, United States, Eepublic, 
 
MOTOR TRUCK TIRES AND RIMS 
 
 285 
 
 JIRERIM 
 
 Kelly- Springfield, Gibney, Swinehart, Hood, Polack, etc., in the 
 single and dual, pressed-on and by some in the demountable 
 types, some of which are il- 
 lustrated. 
 
 These various makes dif- 
 fer in the contour of the tire, 
 the method of producing a 
 firm grip for the hard rubber 
 
 on the steel and the method FIG 26g Republic p resse d-on Type 
 of building up the tire, while Tire, 
 
 the demountables differ in 
 
 rim construction. In some cases the metal base is cut in dove- 
 tail fashion and with grooves, such as the Hood, Polack and 
 Goodrich. In the Gibney and Kelly, the hard rubber is car- 
 ried up to the side of the metal base, while in others it is set 
 straight across the width of the channel base. In some cases the 
 
 FIG. 269. Goodrich DeLuxe Pressed-on and Demountable Types. 
 
 layer of hard rubber is given an irregular wave line surface such 
 as the Goodrich in order to increase the area of contact between 
 the two grades of rubber. 
 
 EUROPEAN TYPE AMERICAN TYPE 
 
 FIG. 270. Polack Pressed-on Type Tire. 
 
 The metal base or rim of a demountable tire has the inner cir- 
 cumference tapered from both sides, its smallest diameter being 
 slightly larger than the outside diameter of the felloe band. 
 Rings which have a tapered surface and are usually termed 
 
286 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 wedge rings, since their cross section is of wedge shape, are in- 
 serted between the felloe band and the tire base. These are re- 
 tained by circular flanges and bolts which pass through these 
 and the felloe of the wheel. 
 
 CENTER WEDGE PI NG^ 
 
 FIG. 271. Kelly-Springfield Demountable Type Single and Dual. 
 
 Most tire manufacturers use this construction; however, the 
 Goodrich demountable differs somewhat in that the wedge section 
 is incorporated in the tire base against which the side flanges 
 press. The rubber portion of a solid tire is usually about 2J ins. 
 high and varies in width according to its design. This, of course, 
 governs the elasticity and cushioning effect. On the large single 
 tires, this height does not give a proper proportioning and to 
 overcome this some makers produce what is commonly called the 
 
 CENTER VYEOGE RiHG 
 
 FIG. 272. Goodyear Demountable Type " SV " Single and Dual. 
 
 European type of tire, in which the rubber is from \ to 1 in. 
 higher. The Goodrich Co. calls this their De Luxe type and 
 while it is designed after the European type, it has quite a dif- 
 ferent contour. Greater resilience is claimed for these types as 
 well as longer life and greater load carrying capacity. A greater 
 carrying capacity is possible, because the contact with the road 
 
MOTOR TRUCK TIRES AND RIMS 
 
 287 
 
 surface is much larger, consequently the weight is distributed 
 over more base area. The greater height of rubber and increased 
 resiliency also give an entirely different traction hold on the road. 
 
 CHANNEL RIM 
 RUBBER 
 CROSS WIRE 
 
 CIRCUMFERENTIAL WIRE 
 FELLOE BAND 
 
 RUBBER 
 HARDRUBB5P 
 TIRE RIM 
 WEDGE RING 
 FLANGE 
 
 BOLT 
 FELLOE BAND 
 
 FELLOE 
 
 EUROPEAN 
 SED-O 
 
 WIRED-ON 
 TYPE 
 
 DEMOUNTABLE 
 
 FIG. 273. Firestone's Variety of Solid Tires. 
 
 Some tire makers recommend this type of tire as an oversize for 
 the American type, since it is made to fit the S.A.E. standard 
 felloe bands. 
 
 The Goodrich Co. has recently introduced a new policy with 
 regard to single and dual tires for heavier truck work. This 
 
 FIG. 274. Goodyear Pressed-on Type " SU " Single and Dual. 
 
 company is recommending a 7-in. single in preference to 4-in. 
 duals and 6-in. singles in preference to 3J-in. duals. The argu- 
 ments are that these singles give better results than the corre- 
 sponding duals, in that often on the road one of the duals has to 
 
288 MOTOR TKUCK DESIGN AND CONSTRUCTION 
 
 take the entire weight of the load on that wheel and that, as it is 
 not designed to take the entire load, it is naturally overloaded 
 and perhaps permanently injured by this frequent caring for the 
 
 RUBBER 
 HARO RUBBER 
 
 EUROPEAN SECTION AMERICAN SECTION 
 
 FIG. 275. Hood European and American Section Pressed Type Tires. 
 
 entire load weight on one wheel. With singles this is not the case. 
 
 Firestone has recently introduced what is known as a giant 
 
 single solid tire made in 8- or 12-in. width. The extra amount 
 
 FIG. 276. Kelley-Springfield Pressed-on Type Single and Dual. 
 
 of rubber is claimed to make it oversize equipment for 6-in. duals 
 and equal equipment for 7-in. duals. The tread has three evenly 
 spaced circumferential grooves in it. 
 
 The Hood Co. recommends its European type of tire for dual 
 equipment, as they claim this type with its greater resiliency will 
 
 FIG. 277. Gibney Wireless Type " MIB " Pressed-on. 
 
 alloV the inside tire to compress more and allow the outside tire 
 to take its share of the load. 
 
 The pressed-on tire will no doubt gain in popularity as it is 
 less expensive than the demountable type, since wedge rings, 
 
MOTOR TRUCK TIRES AND RIMS 289 
 
 flanges and bolts are eliminated, while the firm fit to the wheel 
 also insures the greatest possible mileage. Practically all makers 
 are continuing their demount ables, but the number produced is 
 on the wane. This type will no doubt be continued for some time 
 since powerful hydraulic presses the cost $500 to $700 are re- 
 quired to apply the pressed-on type. This, of course, is a consid- 
 erable outlay for a dealer in proportion to the work he may get 
 at present. However, the demand for trucks is continually in- 
 creasing and, in order to assist the dealer in obtaining his share 
 of the business, some tire companies are selling these presses at 
 the rate of $100 down and $100 per year until paid for, on condi- 
 tion that it is used only in connection with tires made by that 
 company. 
 
 The claim made for the European type of tire is that owing 
 to its higher section and greater resiliency it greatly reduces the 
 cost of upkeep of the mechanism of the truck, and makes it far 
 more comfortable for the driver. 
 
 The Care of Motor-truck Tires. The care of the mo tor- truck 
 tire, while an important item in the maintenance of a commercial 
 vehicle, is not generally understood by operators of these vehicles. 
 All manufacturers of solid rubber tires issue instruction books 
 or cards on this subject, but these, like most all other instruction 
 books, find their way into the tool-box and remain there until 
 trouble arises. Tire makers, however, are endeavoring to edu- 
 cate operators on this subject, and since very little mention has 
 been made regarding this, the writer will endeavor to cover it in 
 such manner as to enable the layman to become familiar with the 
 attention tires require, to give maximum mileage. 
 
 There have been many refinements in the construction of 
 motor-truck tires, and the majority are very dependable; but 
 tires, like the engine, transmission, axles and all other parts of 
 the vehicle, must have a reasonable amount of attention if one 
 expects to obtain the best results. Tire equipment is given care- 
 ful consideration by the engineer and the tire maker in deter- 
 mining the necessary sizes and types. However, no provision 
 can be made for the usage of the vehicle or the care of the tires. 
 Provision is made for taking up wear and alignment in the 
 mechanical parts of the chassis which affect the life of the tires. 
 However, these are not automatic adjustments, and require fre- 
 quent inspections. Tires, like all other parts, have a physical 
 limit, and results can only be obtained if their usage is within the 
 
 20 
 
290 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 limits of their physical strength, which is based upon the com- 
 pression of the vulcanized rubber. 
 
 For maximum tire mileage, three factors the tire, the road 
 and the driver must be considered. The tire must be consid- 
 ered because the type of tire used for quick delivery cannot be 
 used for heavy duty. The road naturally effects the mileage of 
 truck tires, because the bumps and ruts of bad roads throw local- 
 ized shocks on them. The driver, next to the tire itself, is the 
 most important factor. It depends upon him whether the truck 
 be abused. 
 
 In the following an outline of the common injuries to motor- 
 truck tires is given, most of which are sustained in running, and 
 may be traced directly to one of the three factors mentioned 
 above. These common injuries may be summed up as follows: 
 Overloading, speeding, rough roads, wheel alignment and irregu- 
 larities, anti-skid devices, neglected cuts, skidding and applica- 
 tion of brakes, application of power, running in car tracks, heat, 
 oil and grease and abuse of trailers. 
 
 The most premature tire failures are due to overloading, not 
 only by constant overloading, but by the momentary overload- 
 ing as well. Rubber, like any other material, has its limits of 
 resistance, this resistance being its ability to return to its original 
 shape after being compressed. This may be compared with an 
 ordinary rubber band, which will snap if stretched beyond its 
 limit of elongation, as the rubber in a motor-truck tire will snap 
 at once, even though momentarily loaded beyond its limits of 
 compression. This compression is noticeable by the bulging out 
 of the rubber, both left and right and even front and rear. If 
 the load is within the capacity of the tire the rubber will with- 
 stand the strain and as the load is released, return to its original 
 shape, the same as a rubber band when stretched and released. 
 However, if the load is beyond the capacity of the tire the rubber 
 will break down as inevitable as when stretched beyond its limit 
 of elongation. If the tire is overloaded momentarily the rupture 
 may not be apparent, as the broken portions may be hidden by 
 others not noticeably affected, yet the strength of the tire is im- 
 paired and failure of the whole structure is merely a matter of a 
 short time, as the damage is bound to spread. 
 
 The distribution of the load also has an important bearing 
 upon the life of a tire, as trucks are frequently loaded so that the 
 heavy articles are carried near the tail-board, while the forepart 
 of the body carries little. In this case the rear tires usually 
 
MOTOR TRUCK TIRES AND RIMS 
 
 291 
 
 carry an overload, although the total load may be within the 
 capacity of the vehicle. Loads which overhang the rear of the 
 body, such as lumber, pipes, etc., also produce the same effect. 
 It does not matter whether the overload is a constant one or a 
 momentary one as far as the cause of the damage is concerned, 
 and is only material to the extent of the damage. A momentary 
 overload may have ruptured the tire structure only in a single 
 
 FIG. 278. Overloaded, Overspeeded and Bad Road Tire Effects. 
 
 spot, whereas a constant overload will damage the whole tire, 
 thus hastening it to complete failure; but in both cases the tire 
 is doomed to premature ruin. 
 
 Small dual tires are often exposed to momentary overloads, 
 as the camber of the road may be such as to throw the total 
 weight alternately on one of the outer or inner tires, the mates 
 being momentarily relieved of their load. 
 
 Speeding. A tire which is overspeeded is prematurely de- 
 stroyed in a manner very similar to that of an overloaded tire. 
 Overspeeding makes every road rough, because it magnifies every 
 
292 MOTOR TKUCK DESIGN AND CONSTRUCTION 
 
 irregularity and this increases the effect of all shocks. Hitting 
 a curb, bump or any other obstacle with considerable impetus, 
 even though the truck be empty, is in effect identical with a 
 momenary overload, causing a rupture in the rubber structure 
 in that particular spot and gradual ruin of the tire, for as the 
 wheel revolves at excessive speed the rapidity of compression 
 and expansion of the rubber generates internal friction heat. 
 This is increased considerably by the friction of the road, thus 
 heating the rubber to a higher degree than it can resist. This 
 combined with the increased effect of all shocks is very de- 
 structive. 
 
 Rough Roads. Rough roads have an effect on solid rubber 
 tires similar to that of overloading and overspeeding, as the face 
 of the tire rests successively on irregularities which have the 
 effect of overloading that particular portion of the tire. These 
 
 irregularities, such as ruts, 
 large stones, crushed stone, 
 loose brick and similar road 
 materials, cause shocks 
 which tax the tires beyond 
 
 ^ __ _, the limit of their power to 
 
 FIG. 279. Front Wheels out of Line 
 
 due to Striking Curb or Obstacle on the absorb them and these m - 
 Eoad. mentary overloads create a 
 
 disintegrating effect upon 
 
 the tread of the tire. Some roads have an extreme heat which 
 also causes disintegration while others produce a similar effect, 
 owing to their composition. Careful driving over rough roads at 
 moderate speed, avoiding ruts, stones and loose surface material as 
 much as possible, will greatly increase tire mileage. 
 
 Wheel Alignment and Irregularities. Any fault in align- 
 ment allowing the wheels to run out of parallel no matter to what 
 small extent prevents their true rolling motion. When two op- 
 posite wheels are not parallel there is a diagonal grind upon 
 these at the point where they come in contact with the road sur- 
 face. This grinding action quickly wears off the rubber, the wear 
 being very smooth just as though the rubber had been ground 
 off on an emery wheel. 
 
 Misalignment of wheels generally is evidenced through ex- 
 cessive wear on one side or by flats, as these when once started 
 rapidly develop. There are a number of things which affect the 
 alignment of front wheels. The cross rod, axle, or steering 
 
MOTOK TRUCK TIRES AND RIMS 
 
 293 
 
 knuckle may be bent due to violent contact with the curb, another 
 vehicle or obstacle, the cross-rod or knuckle may be improp- 
 erly adjusted, loose or _____ 
 worn hubs, bearings in 
 the wheels and bushings 
 in the steering linkage 
 may be worn, or the ad- 
 justments may have been Fm 280 Front Wheels Qui of Line due 
 
 disturbed through vibra- to Wear or Improper Adjustment. 
 
 tion. 
 
 All wheels should be frequently tested for alignment and 
 always after a collision or untoward event that is likely to effect 
 the wheel adjustments. A piece of tubing fitted with a sliding 
 rod and a thumb screw, or a stair tread extension rule, form a 
 useful gage for front wheel testing. In testing front wheels it 
 is most important that the dead vertical center is measured, both 
 front and rear. This is necessary because of the tendency of the 
 front wheels to spread under the driving force and it is the prac- 
 tice of commercial vehicle builders to set the front wheels at a 
 toe in from one-fourth to five-eighths in. less in front of the 
 axle than in back of it. This allows one-eighth in. to five-six- 
 teenth in. toe in for each 
 front wheel. This is 
 practically taken out by 
 the action of the vehicle 
 on the road, for under 
 momentum the wheels 
 will be approximately 
 parallel. 
 
 Each wheel can also be checked up separately by raising it 
 with a jack and placing a stationary point almost against the 
 wood felloe. Revolving the wheel will determine if the distance 
 between the stationary point and the felloe is the same at all 
 points around the wheel. If the wood felloe rubs at some point 
 around and not at other places it may be due to a slight varia- 
 tion in the felloe, but more usually it is the result of a wheel not 
 running true. 
 
 Irregularities of the driving wheels of a motor vehicle do 
 not exist to the extent that is the case with the front wheels, 
 though it occasionally occurs that when the rear axle is displaced 
 to one side or the other it causes the wheels to take up a diagonal 
 
 FIG. 281. Eear Axle out of Alignment 
 due to Poor Chain Adjustment. 
 
294 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 position with a consequent grinding action upon the tires. It is 
 essential should it be discovered that these are out of parallel 
 that the trouble be rectified immediately. For testing rear 
 wheels, both comparatively and their relation to the front wheels, 
 the ordinary line and rod method cannot be improved upon. 
 The measurement between the wood felloes of the rear wheels 
 should be the same both in front and rear wheels of the axle. 
 Whenever an undue amount of play is discovered in the wheels 
 steps should be immediately taken to remedy the defect, other- 
 wise irreparable damage to the tires is inevitable. 
 
 Anti-skid Devices. Anti-skid devices, especially those which 
 are stationary upon the wheel, contribute a great deal toward 
 causing solid rubber tires to give unsatisfactory service. The 
 loose chain is by far the least injurious as it will work its way 
 around the tire and equally distributes the Avear and strain. 
 However, with a stationary chain this is constantly confined at 
 the point of bearing. 
 
 These anti-skid devices are mostly applied to the driving or 
 rear wheels of a vehicle and these are quite apt to spin in slip- 
 pery places, causing sharp blows at the points of contact. With 
 a sationary device the shock received by the tires in striking the 
 ground is concentrated in a few points around its circumference, 
 causing heavy strains at these points. In order to avoid this, de- 
 vices having numerous cross-pieces should be used for as the dis- 
 tance between these is decreased the force of the blow decreases 
 as the wheel gains momentum. Every type of anti-skid device is 
 more or less injurious to the tire and they should only be used 
 temporarily to pass over soft slippery places. 
 
 Neglected Cuts. Cuts are of common occurrence and are gen- 
 erally caused by road conditions. These cuts, no matter how 
 small, afford an entering place for sand and fine gravel, causing 
 the cut to increase in length and depth. Sand, gravel and other 
 gritty substances are enemies of rubber and once they effect an 
 entry into the tires it is pretty hard to combat them. Cuts near 
 and at the edges are most injurious, and if attended to in time 
 are easily remedied. These should be trimmed off smoothly with 
 a sharp knife as soon as they occur, and if they are not trimmed 
 the revolving wheel causes the loosened edges to catch on every 
 obstruction, so .that the tear constantly increases. When one 
 
MOTOR TRUCK TIRES AND RIMS 295 
 
 unit of a dual tire is permitted to weaken in this manner it causes 
 an overload on its mate. 
 
 Skidding and Application of Brakes. Skidding is generally 
 caused by sudden application of the brakes, turning corners too 
 rapidly and turning corners so small that the crown of the road 
 may cause the rear wheels to skid. The effect of skidding or lock- 
 ing the wheels is quite serious, as this causes flats on the tread 
 of the tires, in addition to placing the tires under side strains, 
 which tears them loose from the base. This same condition will 
 also exist if the brakes do not grip evenly, causing one wheel to 
 roll while the other drags. Turning corners too rapidly increases 
 strain and wear on the tires with a similar effect. Some tire 
 makers recommend truing up tires if flats develop, by turning 
 down the tread, otherwise these will develop rapidly and cause a 
 great loss of mileage. 
 
 The sudden application of power by quick engagement of the 
 friction clutch produces the same effect as locking the wheels. 
 The power applied at the hub starts the rim first and the re- 
 sistance of the road prevents the tire from starting at the same 
 instant. This brief delay slightly stretches, displaces or strains 
 the rubber, just as the life is taken out of a rubber band by con- 
 tinual stretch. This danger is greatly augmented as wear takes 
 place in the driving members, such as the hubs, universal joints, 
 driving chains, etc. 
 
 Running in Car Tracks. Injuries resulting from running in 
 car tracks are serious and readily apparent. Under this condi- 
 tion, the outside edge of the tire rests .upon the raised edge of the 
 car track, so that the distribution of the load is on but a small 
 portion of the tire. That is, the weight of the vehicle is being 
 supported by that small portion of the tire which is riding on 
 the raised part of the track. Throwing the load upon half of 
 the tire causes it to wear rapidly, while the rest of it is in ap- 
 parently good condition. With dual tires this effect is still more 
 pronounced because that part of the unit riding on the car track 
 must sustain the load intended for both tires. 
 
 Heat causes disintegration of the rubber. In winter the large 
 garages are generally heated by steam, the headers of which are 
 fastened close to the ceiling of the floor below. This heats the 
 floor above to quite an extent, and if a heavy truck is parked for 
 two or three days directly over a big hot spot in the floor a con- 
 
296 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
 dition is developed that results in a flat being formed in the tire 
 shortly afterwards. This is due to the action of the heat soften- 
 ing the rubber, while the weight of the truck is resting upon it, 
 causing a flow that never fully returns. 
 
 Gasoline, oil, grease and other fatty substances are solvents 
 of rubber. If garage floors are not kept clean and the tires stand 
 in a pool of oil, a similar action to that of the effect of heat will 
 take place. Grease and oil can easily be removed by a rag satu- 
 rated with gasoline. Gasoline, although a solvent, evaporates 
 quickly and if applied in small quantities will not cause any in- 
 
 FIG. 282. Tires Showing Undue Wear. 
 
 jury if used as a cleansing agent. Another difficulty occurs in 
 the abuse of trailers, which is caused by turning too sharp a 
 corner while loaded. The effects of this are similar to those 
 caused by skidding, as it tends to wrench the inside wheel, twist- 
 ing the tire, which is firmly held to the road by the weight of the 
 load. The results are a loose tire in a very short time. 
 
 The above gives the general abuse of commercial vehicle tires, 
 and while there are numerous others of minor importance, it has 
 
MOTOR TRUCK TIRES AND RIMS 297 
 
 been proven by maintenance engineers that many tire miles can 
 be saved by avoiding the above sources of trouble. In order to 
 obtain maximum tire mileage, commercial vehicle owners should 
 instruct operators to avoid all overloads, momentary ones as well 
 as constant ones, speeding, curbs, ruts, car tracks and reckless 
 backing up against curbs, and also to properly distribute the load 
 and to select the best roads and smoothest pavements. 
 
 Truck operators can save a considerable amount by using 
 judgment in the operation of a commercial vehicle. 
 
CHAPTER XXIII 
 
 ELECTRIC LIGHTING AND STARTING ON COMMERCIAL TRUCKS 
 
 The Advantages and Disadvantages of Electrically Equipped 
 Trucks. Is electric lighting and starting equipment justifiable 
 on commercial cars? Many engineers consider it an unneces- 
 sary complication; others hold that with it economy as well as 
 convenience is gained. A resume of the advantages and disad- 
 vantages may prove interesting especially since the Government 
 specifications for the military trucks included this equipment. 
 
 Many mechanical problems must be considered in selecting 
 electrical equipment for commercial cars. While these units have 
 worked out satisfactorily for passenger vehicles that are equipped 
 with pneumatic tires, it is a question whether they will endure 
 the greatly aggravated vibration of motor trucks having solid 
 tires, stiffer springs and are compelled to travel cobble-stones 
 and rough roads. Such consideration as frequent troubles from 
 inability to withstand the hard usage, are very important and 
 may more than offset the advantages gained through the use of 
 such equipment. It is true that some of these equipments have 
 worked out very satisfactorily on commercial cars ; however, they 
 are generally designed to meet these more exacting conditions. 
 They are sturdier and stronger built devices, while the battery 
 must also be of such capacity as to permit frequent starting and 
 must have some special mounting to resist vibration. 
 
 The arguments for and against electrical equipment, covered 
 in the following, are the result of a general study of this subject 
 and are not based on the opinions of makers of these units. 
 
 Four units generally comprise the complete electric system, 
 the ignition system, the generator, the starting motor and the 
 battery. Ignition systems were previously described and will 
 not be considered in this article. The generating system con- 
 sists of a generator or dynamo, its drive and mounting and also 
 an output regulator and reverse current cutout. The starting 
 system consists of an electric motor, its drive and mounting and 
 a suitable switch for starting purposes. The link between the 
 two systems is the storage battery which serves in effect as a 
 reservoir for accumulating electricity. 
 
 298 
 
ELECTKIC LIGHTING AND 8TAETING 299 
 
 The generators of different systems now in use vary in con- 
 struction or type, some having a permanent and others an excited 
 or wound field. Fundamentally, there are three types of gen- 
 erators in use shunt wound, compound wound and differentially 
 wound generators. The field itself may either carry simple or 
 compound windings. The armature revolving between the poles 
 of the field generates electric current, the output of which is 
 governed by the output regulator. The method of generating elec- 
 tric current was described previously in the chapters of mag- 
 netos. The reverse current output prevents the flow of current 
 through the generator from the battery. 
 
 The starting motor which takes the place of the ordinary hand 
 crank is operated by current from the battery. This unit is sim- 
 ilar but opposite to the generator in that instead of motion pro- 
 ducing current, current flowing through the fields energizing 
 them and causing the armature to rotate produces motion. 
 Speaking loosely, electricity that has been pumped into the bat- 
 tery by the generator, runs out through the motor. If the motor 
 is properly interconnected with the engine it can be made to turn 
 the latter over until it starts. 
 
 A definite amount of work must be done to produce electricity, 
 and that work is done by the generator. The electrical energy 
 that the generator produces is stored in the battery for use when 
 the generator itself cannot supply the current as when the en- 
 gine is to be started. 
 
 Advantages of Electric Lights and Starter. The advantages 
 on a commercial vehicle of electric lights and starter are as fol- 
 lows in their order of importance : 
 
 1. Greater economy due to saving gasoline and time when 
 many stops are made by not keeping the engine running. 
 
 2. Increased life of the engine, as shutting it off at each stop, 
 eliminates considerable needless wear. 
 
 3. Saving of time over hand starting increasing the actual 
 working hours of the car and operator. 
 
 4. Better lighting and easier driving for night work and fewer 
 accidents from the rear light going out. 
 
 5. Better finished appearance of cars for certain classes of 
 work. 
 
 To these may be added the possibility of getting more for 
 certain types of cars for special service, Avhere the advertising 
 value is considered. 
 
300 MOTOE TRUCK DESIGN AND CONSTRUCTION 
 
 Disadvantages of Electric Lights and Starter. The principal 
 disadvantages in equipping commercial vehicles with these units 
 are: 
 
 1. Additional first cost and added complications which the 
 driver does not comprehend. 
 
 2. Increased maintenance cost and interest on additional in- 
 vestment. 
 
 3. Decrease in engine accessibility in making repairs, thus in- 
 creasing the cost of these repairs. 
 
 4. Unreliability of certain parts, such as the storage battery 
 and the possibility of these units being maintained far below 
 their original efficiency. 
 
 5. The effect of vibration on units not originally designed for 
 commercial car service. 
 
 6. Inability to keep the battery sufficiently charged owing to 
 frequent starting and stopping. 
 
 7. Battery and other electrical troubles aggravated by the 
 average commercial car driver not being familiar with the con- 
 struction and care of the electrical system. 
 
 On trucks that have many stops to make such as house to 
 house delivery, starters are no doubt desirable, considering the 
 high cost of gasoline, as the operator will invariably allow his 
 engine to run rather than crank it when making a stop of a few 
 minutes. Stopping the engine will cut down the fuel bills. 
 
 But whether the starter will save time over cranking seems 
 to be disputed. Various arguments are advanced covering the 
 point of economy. 
 
 Any type of delivery car and even some of the large motor 
 trucks make more stops during the day than the average touring 
 car, and from the point of economy the commercial car would 
 seem to have the greater need for a starter. Moreover, the 
 starter is also a convenience and saves energy. Some imagine 
 that the starter will start the engine when the driver cannot start 
 it. This is not true unless the engine is too big to be spun by 
 hand. The average truck engine can be spun easily by the aver- 
 age driver and if the gasoline mixture is getting to the cylinders 
 and the spark is all right, it can be started as many times by 
 man as by a self-starter. A self-starter can do no more than man, 
 but it does conserve his energy. 
 
 Some claim that the time saved with a starter even when 
 stops are numerous is relatively small compared with the time 
 the operator usually wastes in other directions. Cold weather 
 
ELECTRIC LIGHTING AND STARTING 301 
 
 must also be considered, which may average four months per 
 year, when it is really advantageous to let the engine idle and 
 prevent the radiator from freezing and to keep the mixture warm 
 for a good start. 
 
 Stopping will increase the life of the engine, but in the ab- 
 sence of a starter with a bonus system to encourage economy, 
 the driver would not let the engine run idle for long. Where, 
 especially on the heavy vehicles, the drivers' union compels the 
 owner to provide a helper on each car, there is still less excuse 
 to keep the engine running. 
 
 Without question, electric lights are preferable to oil lamps, 
 but it is for the owner to decide, especially whether they are 
 worth their slightly greater cost if there is little operating at 
 night. Accidents that may be traced to the lighting system will 
 be reduced, if the lighting system is maintained at its original 
 efficiency, which is doubtful on a commercial car. 
 
 Where appearance is a large factor, the additional first cost 
 and maintenance are usually disregarded. Under certain con- 
 ditions, especially on light deliveries, electric equipment adds 
 considerable to the sales value. Conditions here approximate 
 those of a touring car and there is no question of that feature in 
 this case. 
 
 Disadvantages Discussed. The first cost of a commercial 
 vehicle is what engineers have been striving to keep down and 
 simplicity aids low first cost. Electrical equipment will add a 
 certain amount of weight and expense that must be paid by the 
 purchaser and as a motor truck is purely a business proposition, 
 its prime object being to carry goods at the lowest cost, the starter 
 must save time and money. From the mechanical viewpoint it 
 means some complications that the average truck driver does not 
 comprehend. He is not an electrician and the best electrical 
 equipment requires some electrical knowledge at times. 
 
 The question resolves itself into Avhether starters can save 
 enough in fuel and time to offset the increased maintenance cost 
 and pay an interest on the additional investment. It should 
 also be remembered that this added equipment will render the 
 engine more inaccessible for repairs, thus adding to their cost. 
 
 There are certain objections from a mechanical standpoint. 
 The battery seems to be the weakest unit of the entire system, 
 for this is subject to jolting and jarring, which shortens its life 
 perceptibly even with the best of care. Spring mounting devices 
 
302 MOTOE TKUCK DESIGN AND CONSTRUCTION 
 
 may overcome this difficulty, but a vast amount of education is 
 necessary before the average truck driver will know how to take 
 care of a storage battery. Even after this lesson has been taught, 
 there still exists that human element which is responsible for the 
 rapid destruction of commercial vehicles through improper care, 
 handling and neglect. 
 
 Frequent starting and stopping is another factor which also 
 must be given consideration, as the battery must be of ample 
 capacity to provide for the number of starts made during a day's 
 work. The generator must be of sufficient size to keep the bat- 
 tery properly charged and it must be also of the simplest type. 
 
 The difficulty resulting from the driver's lack of knowledge 
 will probably diminish as use of the system becomes more uni- 
 versal. 
 
 Opinions of engineers differ as to the final solution of the 
 problem. At present the question of electrical equipment seems 
 to be up to the public, as the personal view of the purchaser ap- 
 pears to be the greatest factor. All makers supplying electric 
 units as regular equipment will omit these if requested to do so. 
 Makers, who do not regularly equip their vehicles with these 
 units, will supply them, if the OAvner will pay the difference. 
 
 The battery seems to be the troublesome unit and the weakest 
 point of the entire system. So far as the lighting is concerned 
 the problem may be solved by sending current directly from the 
 generator to the lamps, similar to the Ford car, but without its 
 irregular lighting characteristics. The starter problem is more 
 aggravated, but may be solved in some as yet unfound, but 
 equally simple, way. 
 
MOTOR TRUCK DESIGN AND CONSTRUCTION 303 
 
 44444 I + + + + 4. 4- 
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 444 + 44+444-4-4- 
 
304 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
MOTOR TRUCK DESIGN AND CONSTRUCTION 305 
 
 I 
 
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 g 
 
 1 
 
 02 
 
 
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 21 
 
306 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
MOTOE TRUCK DESIGN AND CONSTRUCTION 307 
 
308 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
MOTOR TRUCK DESIGN AND CONSTRUCTION 309 
 
310 MOTOR TRUCK DESIGN AND CONSTRUCTION 
 
MOTOR TRUCK DESIGN AND CONSTRUCTION 311 
 
A 
 
INDEX 
 
 Advantages and disadvantages 
 
 of two and four cycle motors 
 
 Advantages of locating motor 
 
 under hood 
 
 Advantages of various motor 
 
 lubricating systems 
 
 Air cooling 
 
 Cushion radiator mounting 
 
 Automatic spark control 
 
 Axle, Bevel-gear type 
 
 Chain-driven 
 
 Double reduction type 
 
 Front bearings 
 
 Built-up type 
 
 Cast type 
 
 Construction of 
 
 Drop-forged type 
 
 Frame attachment of. 
 
 General types of 
 
 Double reduction type of. . 
 
 Internal gear type 
 
 Rear types of 
 
 Shaft-driven types 
 
 Worm-gear type of 
 
 Semi-floating type of 
 Three quarter floating type 
 
 of 
 
 Full floating type of 
 
 Bevel-gear axle 
 
 Brake, adjustments 
 
 Band type 
 
 Concentric type 
 
 Control, lubrication of 
 
 Equalizers 
 
 Hydraulic type 
 
 Internal and external . 
 
 Jackshaf t type 
 
 Linkage 
 
 Location of 
 
 Method of application 
 
 Page Page 
 
 Brake, on shaft-drive models . . 176 
 
 Rear wheel 175 
 
 ^Q Sauer Motor 181 
 
 Shoe type 176 
 
 2 Timken duplex 180 
 
 Types of 172 
 
 38 
 
 39 C 
 
 46 Carburetion 50 
 
 65 Carburetor, Construction of . . 51 
 
 140 Dash adjustment 53 
 
 135 Float, function of 51 
 
 143 Mounting 58 
 
 191 Throttle 52 
 
 190 Troubles 57 
 
 184 Types 52 
 
 184 Cellular type radiator core ... 41 
 
 186 Centrifugal type water pump. . 47 
 184 Center bearing for propeller 
 
 183 shafts 122 
 
 143 Control and pedal mounting 260 
 
 145 Chain drive 132 
 
 154 Driven axle 135 
 
 142 Drive, advantages of 140 
 
 151 Driven front wheel drive.. 163 
 
 154 Jack shaft 133 
 
 Characteristics of two-cycle en- 
 
 154 gines 6 
 
 154 Chassis, definition of 1 
 
 Types, advantages and dis- 
 advantages of 3 
 
 140 Circuit Breaker, the 63 
 
 182 Clutch, band type 102 
 
 177 Comparisons of 102 
 
 179 Gone types 96 
 
 264 Dry P late type 10 
 
 263 Location of 95 
 
 174 Multiple disc type 98 
 
 178 Necessity of 95 
 
 173 Coil ignition 68 
 
 262 Non-vibrating 72 
 
 172 Transformer, type of 68 
 
 172 Compression release 26 
 
 313 
 
314 
 
 INDEX 
 
 Page 
 
 Condenser 64 
 
 Connecting- rod, construction of 15 
 
 Function of 16 
 
 Control, brake, clutch and gear 255 
 
 Conventional type 253 
 
 Locations and their advan- 
 tages 254 
 
 Mounting- of 260 
 
 Progression type of 261 
 
 Sliding shaft type 256 
 
 Spark and throttle .... 255 
 
 Swinging lever typfe 258 
 
 Conversion of reciprocating mo- 
 tion into rotary motion .... 16 
 
 Crank case, the 21 
 
 Construction of 21 
 
 Function of 21 
 
 Crank shaft, construction of . . 15 
 
 Cylinder, construction of .... 14 
 
 Combination type 19 
 
 Grouping of 20 
 
 Cylinder, L-head type 18 
 
 T-head type 18 
 
 Types of 17 
 
 Valve-in-head type 18 
 
 Material of 14 
 
 Cross steering 208 
 
 Differential, function of 125 
 
 Operation of 127 
 
 Bevel gear type 126 
 
 Spur gear type 127 
 
 Lock 128 
 
 Worm gear type 129 
 
 Semi-locking type 129 
 
 Semi-locking type, opera- 
 tion of 130 
 
 Difficulty of transmitting power 114 
 
 Distributor, ignition 65 
 
 Disadvantages of locating mo- 
 tor under hood 3 
 
 Double reduction axle . . . . 143 
 
 Drag link, location of 198 
 
 Lay out of 198 
 
 Proportions of 201 
 
 Types of 209 
 
 Dual ignition systems 67 
 
 Page 
 E 
 
 Electrically equipped trucks, 
 advantages and disadvan- 
 tages of 298 
 
 Electric lights and starter, ad- 
 vantages of .... 299 
 disadvantages of . . 300 
 discussion of ad- 
 vantages 301 
 
 Electric-driven four-wheel drives 171 
 Electromotive force, propor- 
 tions of 79 
 
 Enclosed chain drive 140 
 
 Engine construction 14 
 
 Fan 48 
 
 Location of 48 
 
 Final drive, definition of 132 
 
 Flywheel, function of 17 
 
 Float chamber of carburetor. . 51 
 Four-cycle engine operation . . 8 
 Four-cylinder engine, advan- 
 tages and disadvantages of. . 10 
 
 Four-wheel drive 166 
 
 Combined chain 
 
 and shaft 171 
 
 Electric type of 
 
 drive 171 
 
 Frame, function of 210 
 
 Frame, Trend of design 218 
 
 Pressed steel, advantages of 211 
 
 Cross members 211 
 
 Rigid type 212 
 
 Rigid type effect of 212 
 
 Flexible 213 
 
 Frame, pressed steel, construc- 
 tion of 214 
 
 Structural channel type . . 217 
 Structural I-beam type ... 218 
 
 Tractor type 217 
 
 Friction, definition of 30 
 
 Front and four-wheel drives, 
 
 advantages of 162 
 
 Front wheel, throw off 192 
 
 Function of cam shaft 20 
 
 Of crank shaft, piston and 
 connecting rod 16 
 
INDEX 
 
 315 
 
 Page 
 
 Function of motor lubricating 
 system 29 
 
 Gasoline tank, mounting of . . 246 
 
 Construction of 244 
 
 Bolster type 246 
 
 Pressed steel type .... 248 
 Feed, pressure system 251 
 Systems, advantages 
 and disadvantages of 252 
 
 Gear type water pump 47 
 
 Gear-driven front wheel drive. 166 
 
 Governor, Definition of 85 
 
 Defects 86 
 
 Operation 86 
 
 Centrifugal type 88 
 
 Hydraulic type 89 
 
 Automatic type 89 
 
 Advantages and disadvan- 
 tages of 94 
 
 Gravity, feed fuel system 245 
 
 Heating fuel mixture 57 
 
 High Tension Jump spark igni- 
 tion 60 
 
 Hollow propeller shaft 122 
 
 Honeycomb radiator core 41 
 
 Hotchkiss drive 156 
 
 Spring mounting for . . 239 
 
 Hydraulic type governor 86 
 
 Ignition, systems of 76 
 
 Coil 68 
 
 Low tension make and 
 
 break 59 
 
 Timer 75 
 
 Independent ignition system, 
 
 summary of 67 
 
 Inductor magneto 77 
 
 Operation of 79 
 
 High tension type .... 81 
 
 Shaft 78 
 
 Induction of electrical impulses 62 
 
 Internal gear axle 145 
 
 Page 
 J 
 
 Jack shaft, chain drive 132 
 
 Jump spark, low tension 59 
 
 High tension 60 
 
 Kick switch 69 
 
 Knuckle lever, angles of 194 
 
 Location of . . 195 
 
 Lack of accessability 4 
 
 Lay out of chassis 1 
 
 Live axle drives 168 
 
 Locating motor under seat op- 
 posite hood 5 
 
 Motor under seat 4 
 
 Low tension jump spark igni- 
 tion 59 
 
 Magneto, construction 
 
 of 70 
 
 Make and break igni- 
 tion 59 
 
 Magneto wiring 70 
 
 Lubricants 31 
 
 Requirements of 30 
 
 Lubrication splash system 31 
 
 Circulating splash system 33 
 
 Gravity feed 34 
 
 Force feed 35 
 
 M 
 
 Magneto, classification of .... 60 
 And battery systems low 
 
 tension 69 
 
 High tension 61 
 
 Low tension 69 
 
 Magnetic lines of force 61 
 
 Mechanical oilers 32 
 
 Methods of transmitting power 132 
 
 Mixing chamber 51 
 
 Motor cooling system 39 
 
 Lubrication 29 
 
 Methods of 31 
 
 Speed, method of control- 
 ling 85 
 
 Muffler cutout 266 
 
 Construction of 265 
 
316 
 
 INDEX 
 
 Page 
 Muffler cutout, function of .... 265 
 
 Location of 265 
 
 Types of 266 
 
 Multiple cylinder engines .... 12 
 Multiple feed oiler 32 
 
 Oil pump gear type 32 
 
 Plunger type 32 
 
 Operation of fan 48 
 
 Two-cycle gasoline motor . . 6 
 
 Four-cycle gasoline motor. 8 
 
 Pin type of universal joint .... 118 
 
 Piston construction of 15 
 
 Poppett valves 17 
 
 Power losses in engine 4 
 
 Power plant arrangement 2 
 
 Mountings', description. 320 
 
 Rigid type 221 
 
 Three point type. . 221 
 Three point main 
 
 frame type .... 222 
 
 Floating type 225 
 
 Sub-frame type 226 
 
 Principle of self induction . . 73 
 
 Propeller shaft 122 
 
 Brake 176 
 
 Mountings of 122 
 
 Tubular 122 
 
 Solid 122 
 
 Divided 123 
 
 Slip joint 120 
 
 Pumps, oil 32 
 
 Water 46 
 
 Push rod adjustment 21 
 
 Function of . 21 
 
 Radiator, construction of .... 41 
 
 Built-up type 42 
 
 Mountings 44 
 
 Rebound clips 239 
 
 Rubber, crude 282 
 
 Wild 282 
 
 Cultivated 283 
 
 Manufacturing process of. 283 
 
 Rims . . 284 
 
 Page 
 S 
 
 Safety spark gap 66 
 
 Seat, location of 1 
 
 Solderless Radiator 43 
 
 Spark, fixed 65 
 
 Variable 63 
 
 Spring, auxiliary 235 
 
 Alignment 241 
 
 'Clips 241 
 
 Full elliptic type 234 
 
 Lubrication, of 242 
 
 Mountings of 236 
 
 Overload 241 
 
 Rebound clips 239 
 
 Spring Shackles 239 
 
 Semi-Elliptic type 231 
 
 True sweep type 231 
 
 Double sweep type. . . . 233 
 
 Types of 230 
 
 Three quarter platform 
 
 type 235 
 
 Stewart vacuum feed 250 
 
 Steering gear bevel pinion type 203 
 
 Irreversible type 196 
 
 Principle of 200 
 
 Ratios of 197 
 
 Rack and pinion type 202 
 
 Reversibility of 196 
 
 Screw and nut type 206 
 
 Wheel and Mast 200 
 
 Worm and sector 203 
 
 Worm and wheel 205 
 
 Steering mechanism, descrip- 
 tion of 192 
 
 Switch, function of 66 
 
 Operation of 69 
 
 Tie rod 201 
 
 Location of 197 
 
 Timer, ignition 75 
 
 Tire, care of 289 
 
 Contour and construction 
 of 285 
 
 Demountable type 286 
 
 Tire development 280 
 
 Effect of speeding 291 
 
 Rough roads 292 
 
INDEX 
 
 317 
 
 Page 
 
 Tire, effect of wheel alignment 292 
 Anti-skid devices .... 294 
 
 Neglected cuts 294 
 
 Skidding and applica- 
 tion of brakes 295 
 
 Running in car tracks 295 
 
 Oils, grease, etc 296 
 
 Tire, hard rubber base type.. 284 
 
 Metal base type 282 
 
 Solid truck type 284 
 
 Pressed on type 288 
 
 Torque, definition of 103 
 
 And propulsion, method of 
 
 providing for 155 
 
 Transmission, types of 104 
 
 Friction type 104 
 
 Planitary type 104 
 
 Sliding gear type 106 
 
 Progressive sliding type... 107 
 
 Selective sliding type 108 
 
 Positive clutch type Ill 
 
 Automatic engagement type 113 
 Mounting flexible type ... 228 
 Transforming low tension into 
 
 high tension current 63 
 
 Types of chasses 3 
 
 Of cylinders and their 
 
 parts 13 
 
 Of front wheel drives 162 
 
 Of springs 230 
 
 Of two-cycle engines 6 
 
 Two-cycle engine, advantages 
 and disadvanta- 
 ges of 10 
 
 Characteristics of. 6 
 Two-cylinder opposed motor. . 28 
 
 U 
 
 Unit power plant 22 
 
 Flexible mounting 
 
 of 210 
 
 Universal joint, block and trun- 
 nion type 116 
 
 Page 
 
 Universal joint, cross type .... 115 
 
 Fabric type 121 
 
 Internal gear type. ... 115 
 
 Pin type 118 
 
 Split ring type 115 
 
 Necessity of 114 
 
 Valve, construction of 17 
 
 Function of 17 
 
 Location of 17 
 
 Mechanism for L head 
 
 motor 23 
 
 Valve in head 
 
 motor 24 
 
 Overhead valve 
 
 motor 24 
 
 Operation of 20 
 
 Spring, function of 20 
 
 Vane type water pump 10 
 
 Vaporization of fuel 50 
 
 Variable spark control 83 
 
 Vehicle springs 230 
 
 Vertical tube type of radiator 
 
 core 74 
 
 Vibrator, action of 74 
 
 W 
 
 Water cooling 40 
 
 Pump, types of 46 
 
 Wheel, advantages of steel 273 
 
 Advantages and disadvan- 
 tages of 278 
 
 Cast steel type 272 
 
 Construction of cast steel. 274 
 
 Dual type of 274 
 
 Double disc type of steel. . 276 
 
 Spindle inclination, of 195 
 
 Single disc, type of steel. . 275 
 
 Spoke type of cast wheel. 276 
 
 Wood artillery type 272 
 
 Worm-drive axle 151 
 
318 INDEX 
 
 ATPENDIX. 
 LIST OF PLATES. 
 
 Page Page 
 
 Fagoel heavy duty chassis. . . . 311 Schackt worm-drive chassis. . 310 
 
 Federal 3^-ton chassis 312 Stewart 3J-ton chassis 305 
 
 Kissell general delivery trucks. 309 United stages worm-drive 
 
 Military class B chassis 303 chassis 304 
 
 Muskegon, 2-ton chassis 308 White heavy duty chassis 307 
 
 Packard 5-ton worm-drive 
 
 chassis 306 
 
MOTOR VEHICLES 
 AND THEIR ENGINES 
 
 A practical handbook on their care, 
 repair, upkeep and management 
 
 By EDWARD S. FRASER 
 
 American Bosch Magneto Corporation; Formerly, Captain C. A.. U- S. A., Instructor Motor 
 Transportation Course, Coast Artillery School 
 
 and RALPH B. JONES 
 
 Willys Overland Company; Formerly, Captain C. A., U. S. A., Instructor Motor Transporta- 
 tion Course, Coast Artillery School 
 
 A complete book on the auto- 
 mobile written in the simplest 
 language and with technicalities 
 reduced to a minimum. 
 
 The fundamentals of gas motor 
 operation, as well as the care and 
 operation of the principal acces- 
 sories of motor vehicles are dis- 
 cussed in detail and at greater 
 length than usual. 
 
 The last four chapters are the 
 result of the authors' observations 
 and experience with the great 
 number of trucks, tractors, auto- 
 mobiles and motorcycles operat- 
 ing under their supervision, and 
 a study of them will be of great 
 help in obtaining the maximum 
 economy, efficiency and life of 
 the apparatus. 
 
 CONTENTS 
 
 THE; GAS ENGINE 
 PRINCIPLES OF TWO AND FOUR-CYCLE 
 
 ENGINES 
 
 TIMING 
 
 ENGINE BALANCE AND FIRING ORDER 
 
 COOLING SYSTEMS 
 FUEL FEED SYSTEMS 
 
 FUELS 
 ELEMENTS OF CARBURETION 
 
 CARBURETORS 
 PUDDLE TYPE CARBURETORS 
 
 MAGNETISM 
 
 ELEMENTARY ELECTRICITY 
 BATTERIES 
 INDUCTION 
 
 BATTERY IGNITION SYSTEMS 
 MAGNETOS: ARMATURE TYPE 
 
 MAGNETOS: ROTOR TYPE 
 
 DUAL AND DUPLEX IGNITION SYSTEMS 
 
 STARTING AND LIGHTING SYSTEMS 
 
 POWER TRANSMISSION 
 
 CLUTCHES 
 TRANSMISSIONS 
 
 DRIVES 
 
 DIFFERENTIALS 
 RUNNING GEAR 
 TIRES AND RIMS 
 HOW TO DRIVE 
 ENGINE TROUBLES EXPERIENCED ON 
 
 THE ROAD 
 
 LUBRICATION 
 
 CARE AND ADJUSTMENT 
 
 CARE AND ADJUSTMENT TABLES 
 
 350 pages, 6x9 inches, Flexible Fabrikoid, postpaid $2.00 
 278 pictures, many in colors 
 
 D. VAN NOSTRAND CO., Publishers 
 
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