A drum brake system uses friction to slow the wheel. The parts work together inside an enclosed drum. Here is what brake drum system parts are and what each one does.
Brake Drum
The brake drum is a cylindrical metal housing, usually made of cast iron, that rotates with the wheel. It is mounted on the wheel hub. The inner surface provides the friction surface for the brake shoes. When the shoes press against it, the friction slows the drum and the wheel.
Brake Shoes
Brake shoes are curved metal pieces lined with friction material. When you press the brake pedal, the shoes expand outward against the inner surface of the drum. The friction material on the shoes wears down over time and needs replacement. Brake shoes are a key component among brake drum system parts.
Wheel Cylinder
The wheel cylinder converts hydraulic pressure into mechanical force. It sits between the two brake shoes. When brake fluid enters the cylinder, it pushes pistons outward, which forces the brake shoes against the drum. A leaking wheel cylinder can contaminate the brake shoes and reduce braking performance.
Return Springs
Return springs pull the brake shoes back to their original position when you release the brake pedal. Without them, the shoes would stay in contact with the drum, causing drag and premature wear. There are usually two springs: an upper spring and a lower spring.
Backing Plate
The backing plate is a metal plate mounted to the axle. It supports all the internal drum brake components. The wheel cylinder, brake shoes, and springs are attached to it. It also helps keep dirt and debris out of the brake assembly.
Adjuster Mechanism
The adjuster maintains the correct gap between the brake shoes and the drum as the friction material wears. Some adjusters are automatic and self-adjust when you apply the brakes in reverse. Others require manual adjustment during brake service.
How It All Works Together
When you press the brake pedal, hydraulic fluid pushes the pistons in the wheel cylinder. The pistons force the brake shoes outward against the spinning drum. The friction slows the wheel. When you release the pedal, the return springs pull the shoes back. This happens every time you brake.
