DRUM BRAKE COMPONENTS The backing plate provides a foundation for the brake shoes and associated hardware. The plate is secured and bolted to the axle flange or spindle. The wheel cylinder, under hydraulic pressure, forces the brake's shoes against the drum. There are also two linked brake shoes attached to the backing plate. Brake shoes are the backbone of a drum brake. They must support the lining and carry it into the drum so the pressure is distributed across the lining surface during brake application. Shoe return springs and shoe hold-down parts maintain the correct shoe position and clearance. Some drum brakes are self adjusting. Others require manual adjustment mecha nisms. Brake drums provide the rubbing surface area for the linings. Drums must withstand high pressures without excessive flexing and must also dissipate large quantities of heat generated during brake application. Finally, the rear drum brakes on most vehicles include the parking brakes.
Wheel cylinders Wheel cylinders convert hydraulic pressure from the master cylinder into a mechanical force at the brakes The wheel cylinder bore is filled with When the brake pedal is depressed, additional brake fluid is forced the cylinder. The additional fluid moves the cups and pistons outward. This piston movement forces the brake shoes outward to the contact drum and thus applies the brakes. Piston stops prevent the fluid leakage or air from getting into the system when the pistons move to the end of their bores.