How Do Car Calipers Work?

The caliper on the disc brakes of a car hugs the brake pads to the side of the rotor (also known as disc). The pads are located on both sides of the disc and the caliper covers both the pads and the disc. There is an internal hydraulic piston (and in some applications, there may be two or four pistons) in the caliper that extends outward when pressure is applied to it. The piston applies even pressure to the pads, which then squeeze against the surface of each side of the rotor and by doing so, slow the vehicle down. Think of it in terms of your old bicycle with caliper brakes. The two rubber pads on the front wheel are activated by the tightening of the cable activated by the hand grip on the handle bars. The caliper on the car works in the same manner, except the wheel of the bike is replaced with the side plate of the rotor or disc and the cable of the hand brake is replaced by the foot brake pedal, which distributes hydraulic pressure evenly to the pistons of the caliper(s).

The hydraulic braking system starts at the master cylinder in the engine compartment. Brake fluid is used as the hydraulic fluid. The fluid is plumbed to the braking system on each wheel through a series of steel brake lines. When the foot pedal of the vehicle is depressed, it uses the brake fluid plumbed to each wheel to hydraulically activate the pistons in the calipers to each wheel. Cars most always have calipers in the front for braking applications. Rear disc brakes are now very popular on cars as well. However, some still use rear drum brakes that use a wheel cylinder to hydraulically apply the brakes. Front disc brakes do most of the braking for all cars. Rear brakes, whether disc brakes or not only perform about 20 to 30 percent of the braking for the vehicle.

After time, the pistons of the caliper will press the pads against the rotor and wear down. In some cases, even the pistons of the caliper may fail from constant inward and outward motion. If pistons get stuck, they can create premature pad wear because they would be applying pressure to the pad while the vehicle moved. In the older days, calipers used to be rebuilt by mechanics when they failed, but nowadays the calipers are remanufactured in plants and can be replaced more inexpensively, then rebuilt at the repair shop.