Brake Description and Operation (760) 741-7861

Brake Component Description And Operation

Brake Shoes Warning Lights Front Calipers Rear Calipers
Control Valve Proprotioning Valve Rear Rotor Warning


Vehicles are equipped with leading/trailing brakes, identified by adjuster screw hole in backing plate, located above horizontal centerline of rear axle. All other models are equipped with dual-servo brakes, identified by adjuster screw hole at bottom of backing plate. Brake assembly consists of backing plate, brake shoes, return springs, automatic adjusting assembly and a wheel cylinder. Automatic adjusting assembly consists of an actuator lever, return spring, actuator link, adjusting screw and spring. Automatic adjustment is accomplished through movement of actuating lever and secondary shoe.


Pressure differential warning switch in combination valve energizes brake- warning light on instrument panel when front or rear brakes lose hydraulic pressure. After repairing failed side of hydraulic system, depress brake pedal with moderate to heavy pressure to hydraulically center the piston. This will turn off brake warning light. On vehicles with Hydro-Boost, insufficient flow of power steering fluid to the hydraulic booster system will turn on brake warning light.


Front brakes are floating caliper or sliding caliper design. Rear brakes are sliding caliper design. Caliper is attached to caliper mount. Caliper is mounted to steering knuckle or caliper adapter, depending on application. Caliper assembly slides back and forth in machined cutouts.


The rear disc brakes use a Bendix caliper. The caliper mounts to the anchor plate in a way that allows the caliper to move laterally against the rotor. The calipers a one piece casting with the inboard side containing a piston bore. A square-cut rubber seal fits in a groove in the piston bore to provide a hydraulic seal between the piston and caliper bore.


Combination Valve

System uses a combination valve to regulate brake system hydraulic pressure. Combination valve, located in brake lines between master cylinder and wheels, has 3 pressure control functions: l Metering (or hold-off) section of valve limits pressure to front brakes until pressure of rear brake shoe retractor springs is overcome, then allows pressure to front brakes. l Warning switch section of valve constantly compares front and rear brake pressures from master cylinder.

Proportioning section of valve allows input pressure to rise to predetermined level before allowing output pressure to rear brakes. This prevents rear wheel lock-up on vehicles with light rear wheel loads. Combination valve also contains a by-pass feature. This ensures full system pressure is applied to rear brakes if front brakes lose hydraulic pressure (or if rear brakes lose hydraulic pressure, full pressure is applied to front brakes.

Height-Sensing Proportioning Valve

Valve senses vehicle load conditions through relative movement between rear axle and body. As vehicle load increases (resulting in decreased vehicle height), valve allows higher pressure to rear brakes, resulting in optimum front-to-rear brake pressure balance.


The rear disc brakes use a combination rotor and hub assembly. The rotor is integral with the rear hub. During operation, the rotor turns between the linings and basically free wheels until the linings begin to apply a clamping action on it. The vented area between the rotor braking surfaces allows for efficient heat dissipation.


On vehicles with height sensing proportioning valve, use of aftermarket load leveling kits, air shocks, or modifications that change axle-to-frame distance will provide a false reading to valve. False readings may result in unsatisfactory brake performance.