BRAKING COMPONENTS

Drum brake components and operation


1. Drum

The drum rotates with the wheel and axle. When the brake shoes are pressed against it, the rotating speed of the drum and wheel, and thus the speed of the car, are reduced. The drum absorbs and dissipates heat. Some designs have cooling vanes which increase the friction surface area and aid cooling.

2. Brake cylinder and pistons

Brake cylinders (wheel cylinders) convert pressure from the hydraulic system into the mechanical force which pushes the brake shoes against the drum. The most common type is the double-piston wheel cylinder, containing one piston at each end to operate the shoes.

3. Brake shoes and linings

The brake shoes are the components that the wheel cylinder pistons act on, pushing them outwards to rub against the drum. A brake lining (friction material) is riveted or bonded to each shoe.

4. Backing plate

The brake shoes and wheel cylinders are mounted on a backing plate, which is normally made of heavy-gauge steel. One of its most important parts of the backing plate is the anchor, or on some designs, the anchor pin. This is the fixed point rest that the ends of the brake shoes rest on and the point through which the vehicle’s kinetic energy is transmitted.

5. Adjuster mechanism

The adjuster mechanism automatically adjusts the distance between the shoe and drum as the lining wears down. Play the animation to see how it works.

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