On the Peerless truck, the jack shaft is built integral with the transmission as shown in Fig. 113. It is similar to the construction 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 protected from mud and water. Construction of this type may also be found on several other cars.
Fig. 109. Sheldon Jack Shaft.
Fig. 110. Velie Jack Shaft.
Fig. 111. Velie Rear Axle.
Fig. 112. Atterbury Radius Rod.
The Vulcan radius rod and rear axle construction differ somewhat 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 roar end has three bosses, through which are inserted two guide pins and an adjusting screw. These guide pins are retained by clamping bolts, while the adjusting screw is attached 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 and attached to the wheel by bolts and the wheels are mounted on roller bearings.
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 differential carrier or housing which carries the entire differential assembly and also the transmission. Provision is made for inspection 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.
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 rod. The hall sleeves accommodate a roller bearing held in position against the shoulder of the drive shaft by a large lock nut properly secured by lock wires. A large adjusting nut. containing a felt washer screwed into the end of the hall sleeve, bears against the outer race of the hearing. Sprockets are bolted to the flanges forged integral with the drive shafts and the bolts are equipped with hardened steel bushings. They afford equal distribution of the shearing strains on the bolls, due to the drive of the truck.
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-benm section with integral spring pads.
The G.M.C. one-, one-and-a-quarter and two-ton models have similar constructions excepting for size, which varies on the different 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 anil 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 reactions are taken on the radius rod. This radius rod is divided into a front and rear part, each having a large threaded boss to receive 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.
An enclosed chain drive is illustrated in Fig. 118. This construction has been used on the Natco one-ton trucks for several years. The ease 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 provides 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 flexibility, 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 adjusted 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 necessary, 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 maintenance cost.
Fig. 113. Peerless Jack Shaft Intregal with Transmission.
Fig. 114. Vulcan Radius Rod with Adjustment at Hear End.
Fig. 115. Kelley-Springfield Floating Jackshaft with Pressed Steel Housing.
Fig. 116. Kelley Radius Rod, Brake and Rear Axle Construction.
Fig. 117. G.M.C. Radius Rod and Rear Construction.
Fig. 118. Enclosed Chain Drive.