How Brake Rotors Work

The Rotor or Disc

Disc brakes are named after the rotor. Most vehicles have used disc brakes in the front of vehicles for many years. Now, many vehicles are offering four-wheel disc brakes which are more effective and easier to replace than drum brakes. Front discs or rotors are two flat pieces of forged metal plated together with vents in between. The vents assist the rotor in cooling since the friction of the pads against the surface of the rotor creates intense heat. Think of the rotor as a front wheel on a ten-speed bicycle or a mountain bike. The rotor is mounted to the knuckle under the wheel and it moves in a rotating motion with the wheel. When you pull the caliper hand brake on the handle bars of your bicycle, two hard rubber pads, one on each ride of the rim of the bicycle tire, press together and slow the bicycle down. When the brake is applied, the caliper sitting over the rotor activates a hydraulic piston which squeezes the brake pads, one on each side of the rotor, against the plate of the rotor applying even pressure and slows the vehicle down.

The Caliper

Although all of the components of disc brakes are important, the most important one of all is the caliper. This is the device that activates the pads against the rotor. The caliper works from a series of hydraulics that start with the master cylinder located in the engine compartment. The hydraulic fluid is brake fluid. The fluid is plumbed to the braking system of each wheel through a series of steel lines. These lines carry the hydraulic fluid to the hydraulic components of each wheel. By pressing on the brake pedal, a power brake booster applies hydraulic pressure from the master cylinder, through the steel lines, to each hydraulic component at each wheel. The caliper is used in disc brakes and covers the rotor, hugging it as it stands vertically with the wheel. Brake pads are inside the caliper, but one on each side of the rotor. As the hydraulic pressure activates, the piston of the caliper extends in an outward motion and squeezes the pads and the plated flat surface of the rotor, slowing down the vehicle.

The Brake Pad

The most commonly worn part of the disc braking system is the pad. The friction material mounted on the face plate of the pad is less aggressive in composition to the surface of the rotor. Just the like bicycle uses hard rubber pads, because if it used something more aggressive, it would harm the wheel of the bike. After time, the friction material of the pad wears down, as does the rotor to a degree, but a whole lot more slowly than the pad material. However, nowadays, the rotors are made thinner and more affordable so to properly replace pads, many mechanics opt to replace the rotors opposed to machining them (or matching them) on a lathe to resurface them.