Disc brakes are not a new device, in fact Fred Lanchester designed and patented a disc brake design in the early 1900's pioneering days of motoring before drums became the de-facto standard. It was'nt until the 1950's that disc became popular, first in racing applications in which the D type jaguar was an early adopter, and then moving to road cars, firstly sports types like the Triumph TR range and the E-type, before becoming standard (on the front) on All cars. The difficulty and extra cost of arranging a parking brake kept them off the rear wheels of most cars for many decades, but now many if not most modern cars use them at both ends.
The most common type of disc brake on modern cars is the single-piston floating caliper.
Other cars have had dual , four piston or even six piston fixed caliper designs. A piston (or two or three) on each side of the rotor pushed the pad on that side. This design has been largely eliminated because single piston designs are cheaper and more reliable, Multi-piston designs are now generally found on high-end motors and sports cars .
What's In a Disc Brake?
The main components of a disc brake are the:
Parts of a disc brake
How It Works
The disc brake is a lot like the brakes on a bicycle. Bicycle brakes have a caliper, which squeezes the brake pads against the wheel. In a disc brake, the brake pads squeeze the rotor instead of the wheel, and the force is transmitted hydraulically instead of through a cable. Friction between the pads and the disc slows the disc down.
A moving car has a certain amount of kinetic energy and the brakes have to remove this energy from the car in order to stop it. How do the brakes do this? Each time you stop your car, your brakes convert the kinetic energy to heat generated by the friction between the pads and the disc. Most car disc brakes are vented, which means a set of vanes, between the two sides of the disc, pump air through the disc to providing cooling.
Disc Brakes are Self-Adjusting
The single-piston-floating caliper disc brake is self-centering and self-adjusting. The caliper is able to slide from side to side so it will move to the center each time the brakes are applied. Also, since there is no spring to pull the pads away from the disc, the pads always stay in light contact with the rotor (the rubber piston seal and any wobble in the rotor may actually pull the pads a small distance away from the rotor). This is important because the pistons in the brakes are much larger in diameter than the ones in the master cylinder. If the brake pistons retracted into their cylinders, it might take several applications of the brake pedal to pump enough fluid into the brake cylinder to engage the brake pads.
Emergency Brakes on Cars with Disc Brakes on All Four
An emergency brake has to be actuated by a separate mechanism than the primary brakes in case of a total primary brake failure. Most cars use a cable to actuate the emergency brake.
Some cars with four wheel disc brakes have a separate drum brake integrated into the hub of the rear wheels. This drum brake is only for the emergency brake system, and it is actuated only by the cable; it has no hydraulics.
Other cars have a lever that turns a screw, or actuates a cam, which presses the piston of the disc brake.
Disc brake with Parking brake