Automotive Q & A

Knowledge Database - Brakes

Question: How do rear disc brakes work?

Answer: Rear disc brakes are basically the same thing as front-wheel disc brakes. Let’s discuss what a disc brake is before we get into why rear disc brakes are different than front disc brakes. Disc brakes are responsible for stopping your vehicle. They consist of three main parts: brake pads, a caliper, and a rotor. Brake pads are located on each side of the rotor and are actually pushed against the rotor to stop the wheel and thereby stop your vehicle. The pads create the necessary friction to stop the vehicle. The caliper is a device located over the top of the rotor and contains both brake pads. There are two types of calipers: floating calipers and fixed calipers. A floating caliper can compress itself and contains only one piston. When the brakes are applied, brake fluid will force the piston into the brake pad, which will press against the rotor. Then, the other side of the caliper will press the other brake pad against the rotor to stop the wheel and vehicle. A fixed caliper doesn’t move; so, it contains two pistons located on each side of the rotor. When the brakes are applied, brake fluid forces both pistons into each brake pad, which press against each side of the rotor, to stop the wheel and vehicle. The rotor is an iron disc connected to the tire’s hub. Rotors work hand-in-hand with brake pads to stop your vehicle. Again, when you step on your brake pedal, your vehicle’s brake pads are compressed against the rotor creating friction. This friction enables your vehicle to stop while also creating a tremendous amount of heat. Rotors consist of two iron discs connected by ribs. When the brakes are applied, the brake pads are pressed to both iron discs. There are many different rib designs for rotors, but they all do the same thing. They aid in dissipating the large amounts of heat created by the friction between the rotor and brake pads. These ribs allow the hot air to vent from the rotor and also direct air in to cool the rotor. It is very important for rotors to be able to dissipate the large amount of heat so they can work properly. Now that we covered how disc brakes work, let’s discuss the difference between rear and front disc brakes. The only difference is that rear disc brakes must include a parking/emergency brake. Parking brakes must be completely separate from your vehicle’s regular hydraulic brakes in case your regular brakes ever completely failed. There are two ways a parking brake is connected to a rear disc brake. First, rear disc brakes contain a corkscrew device that, when the parking brake is applied, pushes a piston into the brake pad to stop the vehicle. Rear disc brakes can also include a separate drum brake system so that when the parking brake is applied, the parking brake’s cables will pull a lever in the drum brake that compresses the brake shoes to stop the vehicle.

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