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Caliper Basics

Brake calipers are simple basic components used to apply pressure and stop the rotor from turning which will reduce the vehicle speed. Brake calipers generally house one or two pistons while others can have up to four depending on the application (heavy duty or performance). Calipers can be bolted in a fixed position or can be a "floating" type. The fixed type, usually 2-4 pistons, are bolted to a bracket or the spindle. The pads are configured in such a way that when hydraulic pressure is applied to the pistons, the pads are forced out against the rotor producing the braking action.

The other type of caliper, usually single piston, uses a floating action. With this configuration, the caliper is free to "float" or move on a pair of pins, bolts, or slides. When hydraulic pressure is applied, the piston pushes the inboard pad to the rotor while the outboard pad is pulled against the rotor stopping the disc from rotating.

Calipers consist of a housing, piston(s), seals, dust boot, and a bleeder valve. The pistons can be made of phenolic or steel. The phenolic piston consists of a phenol-formaldahyde resin that is light weight, heat resistant, non-corroding, and resists heat transfer.

Most common reasons for failure are:

  • Corrosion caused by internal water intrusion (brake fluid absorbs water).
  • Sticking or frozen pins, bolts, or slides that causes excessive inboard pad wear.
  • Contamination from the brake system.
  • Improper fluid when used in a system which uses a petroleum based fluid will cause all rubber components in the brake system to swell.

  • Frozen bleeder valves in the caliper housing due to external corrosion.
  • Overheating due to residual pressure from the brake system not allowing the piston to return.
  • On rear calipers, failure to use the parking brake regularly causes the parking mechanism to corrode and keep the caliper properly adjusted.

IMPORTANT: Calipers should be replaced in pairs to prevent uneven braking. The brake system should be thoroughly flushed with the recommended fluid from a sealed container and the sliding surfaces must be lubricated with the proper grease for your application.

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