Rick's Free Auto Repair Advice

How a brake caliper works

How a brake caliper works

Most vehicles are equipped with “floating” brake calipers. Floating brake calipers have one or two pistons on just one side of the caliper. As the brakes are applied, fluid pressure forces the piston(s) out of the caliper bore. The piston(s) force the inboard brake pad against the rotor until the pad can’t move any further. At that point, an equal-and-opposite reaction occurs and the brake fluid pressure pushes the caliper body away from the brake rotor. That causes the caliper “fingers” on the outboard side of the caliper to pull the outboard brake pad against the outward-facing side of the rotor. A floating caliper slides on two brake caliper slide pins.
brake caliper and brake pads

brake caliper

Brake caliper at rest. Notice the position of the square-cut O-ring seal

brake caliper applied

Brake caliper applied. The piston is forced out by brake fluid pressure. The square cut O-ring seal twists forward. Upon release, the O-ring seal untwists and returns to its original shape, pulling the piston back into the bore

How disc brakes work diagram

Since the inboard pad can’t move any further, the pressure in the caliper bore forces the entire caliper to move in the opposite direction (#4). That pulls the outer edge of the caliper (#5) and the outboard brake pad (#6) against the rotor.

©, 2021 Rick Muscoplat

Posted on by Rick Muscoplat

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