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 whiffltree type. The brake linkage is dependent upon the general layout of the chasis.
With the seat mounted over the engine, it is necessary to arrange this so it will provide maximum accessibility for the engine, and Fig. 248 illustrates how this is accomplished with win-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 eqanlizers of the whiffltree 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.
On the Natco trucks (Fig. 244) the engine is mounted under a hood and the linkage consists of rods throughout.
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 ope rates the service brake, while the brake pedal has a ratchet which locks automatically and is released by tipping the pedal pad. The brake equalizer is of a modified whiffletree type and is mounted vertical instead of horizontal.
245, in which the ordinary brake levers which usually form connections for the modified form of whiffletree equalizer are replaced 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 applied 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.
Most brake shafts and their hearings are lubricated grease cups; however, on the La France trucks the brake shaft assembly (Fig. 240) 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.
Fig. 244. Nateo Brake Rod and Pedal Arrangement.
Fig. 245. Peculiar Brake-Rod Equalizer of the U. S. Truck.
Fig. 246. Wick Oiling System on the La France 2-Ton Truck Brake Shafts.