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Module 2 - Hydraulic System Components (Page 4 of 5)

Hydraulic System Components

Wheel Cylinders

Drum brakes use wheel cylinders.

Wheel cylinders normally have two pistons and two cups in a cylinder of metal. The fluid is sealed between the two pistons by cup seals.

Hydraulic pressure keeps the lips of the seal tight against the bore preventing fluid from leaking out and air from being drawn into the system. The cups are also held in position by a spring to maintain a tight seal.

The wheel cylinder is mounted solidly to the backing plate. The backing plate is, in turn, mounted to the axle or spindle assembly. Therefore the backing plate is always stationary relative to the motion of the wheel.

The brake shoes are also fastened to the backing plate assembly.

Module 2 (Page 4 of 5)