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Module 1 - More on Drum and Disc Brakes (Page 3 of 3)

Disc Brakes

Disc brakes use brake pads mounted in a caliper that contacts a rotor. The friction created between the rotor and the brake pads will slow and stop the vehicle. Friction generates heat, and heat is dissipated / released into the air.

Advantages over drum brakes

Disc brakes pads are smaller that drum brake shoes. Therefore, disc brakes have a reduced contact area compared to drum brakes. They can dissipate heat more quickly and are less likely to fade. Brade fade occurs when the brake rotors and pads overheat. When this happens, the co-efficient of friction is reduced which reduces the braking efficiency. In other words, brakes get hot means it is harder to stop.

Since front disc brakes do most of the braking (up to 80% of the brake load) they are expected to wear out a lot faster than the rear brakes. It is common to replace two or even three sets of front brakes pads before replacing one set of rear brake shoes. Therefore brake pads use a wear indicator device. It is simply a scraper that makes noise when it contact the brake rotor. See diagram below.

Brake rotor distortion is reduced because the force of the pads is applied equally to both sides rather than on one side only. In addition, surface contact is more accutate and consistent than with drum brakes. Disc brakes are also more efficient in converting kinetic energy (energy in motion) to heat energy.

Disc Brakes Categories

Disc brakes are categorized according to the style of application. These include:

1. Fixed caliper

Fixed calipers have pistons on both sides of the rotor and are firmly mounted to the steering knuckle of the vehicle. When the driver presses the brake, both pistons are activated on both sides of the caliper. The pistons on each side of the caliper force the pads against the brake rotor.

2. Floating caliper

Floating caliper brakes (also called sliding caliper) will have one or more pistons on one side of the rotor. When the brakes are applied, the piston forces the brake pads against the rotor on the piston side. The force is transmitted through the caliper, moving it along bushings or in machined grooves on the caliper mount. The caliper continues to move until the opposite pad contacts the rotor.

Floating or sliding calipers have some advantages over fixed calipers. Floating calipers have fewer parts, therefore they are cheaper to manufacture and simpler in operation. Floating calipers are self-centering.

Module 1 (Page 3 of 3)