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, 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 adjustment can be obtained without removing the wheels. Another feature is the provision of large grease cups and liberal grooves for lubricating the various shaft hearings.
Fig. 151. Natco Double Rear Wheel Brake.
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 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.
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 reduction axles universally using the double rear-wheel brake.
Fig. 152. Pierce-Arrow Propeller Shaft Brake.
The Pierce-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 operating 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 engagement 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 1/2-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.
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.
The Clark Equipment Company offer an excellent example of internal and external rear-wheel brake (Fig. 154) in the construction employed on its internal 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 brake hand brackets and so arranged that they can easily be renewed. The forward end of the brake is supported by an extension of the brake spider and has liberal provisions for adjustment. An excellent feature in connection with this brake is the provision of a metal disc and packing separating the gear compartment from that of the internal brake. This, in addition to making it possible to lubricate the gears with graphite, guards against the breakage of the gears in case any part of the brake mechanism should come loose.
Another good example of internal and external brake construction is shown in Fig. 155 and used on the Autocar. The external 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 internal brakes are also of the shoe type, fabric-lined and hinged to the brake spider. They arc expanded by a double-armed lever which is connected to thorn 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.
Fig. 154. Clark Internal and External Brakes.
Fig. 155. Autocar Internal and External Brakes.