Not all passenger vehicles have brake calipers. The older a car is, the less likely it is to have them. There are two common braking systems. The first, drum brakes, is the old industry standard.
Although still used in new cars, they are typically only on the rear brakes. The newer system of disc brakes is used on the front brakes of most new cars. Increasingly, cars are being built with disc brakes both front and rear.
Brake calipers are one of the lesser known components of the disc brake system, however they are essential. The most often replaced - and therefore best known - component is the brake pads. These are thin piece of metal with a layer of friction material. They are replaced when the friction layer wears off.
These pads contact the rotors - the next best known component of the system. A rotor is essentially a large metal disc (hence the name disc brakes), it is attached to the wheel or the axle. Therefore, when the rotors are slowed down by the friction of pads against them, they in turn slow the wheels. So, what makes the brake pads press against the rotors when you step on the pedal? That's where your calipers come in.
The brake calipers are the housing for the pads. They are made of metal and shaped somewhat like a clamp. They are independent of the wheels and rotor but sit over the rotor - like a clamp that has not been tightened. The brake pads go on the inside of these calipers, attached to the caliper on the side toward the rotor.
Between the brake calipers and the brake pedal lies hydraulic lines. The hydraulic lines, and the fluid reservoir called the master brake cylinder, are filled with brake fluid. This is a special type of hydraulic fluid, used specifically for braking systems. When the brake pedal is pressed, fluid from the master cylinder flows through the brake lines to the calipers.
Although the brake calipers are immobile, they contain pistons which this hydraulic pressure forces to move. These pistons in turn push the brake pads against the rotor - creating the necessary friction.
There are different types of brake calipers in use. Aside from the typical variation among manufacturers and models, the biggest difference between them is the pistons. The most common system uses a single piston within a cylinder. Some vehicles, however, have more pistons. High performance vehicles, such as race cars, may have as many as twelve pistons in the brakes. While the first disc brakes used a single hydraulic system for all wheels, most newer cars have separate hydraulic circuits for each wheel. This is a safety measure, against total brake failure.
The disc braking system is considered to be superior to the older drum braking system for several reasons. They boast easier and often less costly repairs, However, the most important factor is safety. Brake fade is a common problem with these systems, caused by gasses building up in the drum. Disc braking systems, however, do not have this problem as such gasses do not collect in the calipers.