Disc brake components and operation

1. Calipers and pistons

Brake calipers are basically U-shaped clamps that fit over the disc and pads. A caliper contains at least one hydraulic cylinder. This converts hydraulic system pressure into the mechanical force that squeezes the pad against the disc.

There are two main disc brake designs, determined by the caliper arrangement:

a. Fixed caliper (Opposed piston)

b. Floating caliper



Fixed caliper (Opposed piston)

In this design, the caliper is attached to the hub carrier and is stationary. A minimum of two opposing pistons are used.

Some fixed calipers are equipped with springs behind the pistons to keep them from retracting too far from the disc. This ensures a firm pedal feel.




Floating caliper

The floating caliper uses one or two pistons, positioned on only one side of the caliper. The caliper is mounted on guide pins which move freely back and forth within bushings. Hydraulic pressure behind the piston pushes the inner brake pad against the disc.

Simultaneously, the inside of the caliper is pushed away from the disc. This pulls the outside of the caliper and the outer brake pad against the disc.The sliding caliper is a variation on the floating caliper design. Instead of guide pins it uses machined sleeves to position and align the caliper.
Floating calipers have some advantages over fixed calipers:

- Powerful action without the complexity of multiple pistons
- Easier servicing
- Cheaper manufacturing





2. Brake pads

A brake pad is composed of a steel backing plate with friction material (brake lining) riveted or bonded onto it. Additional layers are usually added for noise, vibration and heat management.





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