The Front brake discs also endure frictional wear and eventually thin over time. Vehicle manufacturers specify a minimum thickness for brake discs and stress that these must be replaced prior to this point for safety reasons. Brake discs have to be replaced as an axle pair and the brake pads must be changed at the same time. Cast iron is an ideal material for brake components, but can corrode easily. Most of the braking force is exerted by the front brakes thus any surface rust is quickly cleaned off by the action of the pads on the discs. The braking force is much lower on the rear, especially on a small light vehicle and may not be sufficient to clean corrosion from the surface of rear discs, particularly if the vehicle is used only infrequently and for short trips.
Drum brakes front and rear used to be the norm but as vehicles became more powerful in the 1960s more and more manufacturers began to fit disc brakes to the front – to provide most of the braking effort – while retaining drum brakes on the rear to provide the parking brake function.
Brake Fluid: A special purpose high-boiling point fluid that transmits the hydraulic pressure generated by the master cylinder to the brake units
Fluid Reservoir: Holds a supply of reserve fluid to feed the master cylinder when needed. A sensor (normally situated on the reservoir cap) detects if the fluid level falls too low and sets an indication on the dash
Master Cylinder: The single-piston cylinder that transforms the applied pedal force into an hydraulic pressure which is transmitted simultaneously to all four wheels
Brake Servo: A vacuum assisted component used on motor vehicles in their braking system, to provide assistance to the driver by decreasing the braking effort
Brake Lines/Hoses: These steel lines carry brake fluid from the master cylinder to the brakes. For most of their length they are attached to the body with clips or brackets to prevent damage from vibration. Brake Hoses are flexible tubes that carry the brake fluid from the wheel arch to the calipers
Discs: Discs are made of cast iron and are either be solid or vented (when they require extra cooling). Using calipers to squeeze pairs of pads against a disc in order to create friction that retards the rotation of the vehicle axle.
Calipers: An assembly which houses the brake pads and pistons. There are two types of calipers, a fixed type that uses one or more pairs of opposing pistons to clamp from each side of the disc. A sliding type that moves 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.
Pads: These are steel backing plates with friction material bonded to the surface that faces the disk brake
Drums: These are a cast iron housing that rotates with the wheel and axle. When the brakes are applied, the shoe lining pushes radially against the inner surface of the drum, and the ensuing friction slows or stops rotation of the wheel
Shoes: 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
Wheel Cylinders: One wheel cylinder operates the brake on each wheel. Two pistons operate the shoes, one at each end of the wheel cylinder. Hydraulic pressure from the master cylinder acts on the piston cup, pushing the pistons toward the shoes, forcing them against the drum.
The mechanical operation of the parking brake is effected by a lever or a foot pedal which in turn uses cables to activate or deactivate the parking brake.
Disc Parking Brake:
Drum Parking Brake:
Caliper Parking Brake:
Electronic Parking Brake: