Brake Parts

An ABS Sensor measures the speed of wheel rotation under braking. ABS works on the principle of braking a wheel until it just begins to skid (this is the point where braking efficiency would drop off dramatically) and then releasing the brake pressure and re-applying the brakes. ABS sensors identify the skid point and trigger a release in brake pressure. As the cycle is repeated many times a second, the driver will feel a rapid pulsing and hear a chattering noise as ABS is applied.

For drum brakes to function correctly, the brake shoes must remain close to the drum without touching it. If they get too far away from the drum (as the shoes wear down, for instance), the piston will require more fluid to travel that distance, and the brake pedal will sink closer to the floor when the brakes are applied. This is why most drum brakes have an automatic adjuster. Each time the car stops while in reverse, the shoe is pulled tight against the drum. When the gap gets big enough, the adjusting lever rocks enough to advance the adjuster gear by one tooth. The adjuster has threads on it, like a bolt, so that it unscrews a little bit when it turns, lengthening to fill in the gap. When the brake shoes wear a little more, the adjuster can advance again, so it always keeps the shoes close to the drum.

Brake cables are used to activate the brakes.

The brake caliper is the assembly which houses the brake pads and pistons. The pistons are usually made of aluminum or chrome-plated steel. There are two types of calipers: floating or fixed. A fixed caliper does not move relative to the disc. It uses one or more pairs of opposing pistons to clamp from each side of the disc, and is more complex and expensive than a floating caliper. A floating caliper (also called a “sliding caliper”) moves with respect to the disc, along a line parallel to the axis of rotation of the disc; a piston on one side of the disc pushes the inner brake pad until it makes contact with the braking surface, then pulls the caliper body with the outer brake pad so pressure is applied to both sides of the disc.

The disc brake or disk brake is a device for slowing or stopping the rotation of a wheel. A brake disc (or rotor in U.S. English), usually made of cast iron or ceramic composites (including carbon, kevlar and silica), is connected to the wheel and/or the axle. To stop the wheel, friction material in the form of brake pads (mounted on a device called a brake caliper) is forced mechanically, hydraulically, pneumatically or electromagnetically against both sides of the disc. Friction causes the disc and attached wheel to slow or stop.

A drum brake is a brake in which the friction is caused by a set of shoes or pads that press against the inner surface of a rotating drum. The drum is connected to a rotating wheel.

Brake pads are an important part of braking systems for all types of vehicles that are equipped with disc brakes. Brake pads are steel backing plates with friction material bound to the surface facing the brake disk.

The brake shoe carries the brake lining, which is riveted or glued to the shoe. When the brake is applied, the shoe moves and presses the lining against the inside of the drum. The friction between lining and drum provides the braking effort and energy is dissipated as heat. Modern cars have disc brakes all round, or discs at the front and drums at the rear. An advantage of discs is that they can dissipate heat more quickly than drums so there is less risk of overheating. The reason for retaining drums at the rear is that a drum is more effective than a disc as a parking brake.

The master cylinder is a control device that converts physical pressure (commonly from a driver’s foot) into hydraulic pressure to operate other device(s) in the hydraulic system. The most common automotive uses of master cylinders are in brake and clutch systems. The operated device in the clutch system is called the slave cylinder. In brake systems, the operated devices are brake calipers and/or wheel cylinders.

A wheel cylinder is a component in a drum brake system. It is a device usually located above the shoes at the top of the wheel. Actuated by hydraulic pressure, it pushes the brake shoe outward against the drum.