Brake Caliper

📖 YOUCANIC Automotive Glossary

A brake caliper is a hydraulic clamping device that houses the brake pads and uses hydraulic pressure from the master cylinder to squeeze the pads against the brake rotor, creating the friction needed to slow and stop the vehicle. When you press the brake pedal, brake fluid pressure (typically 800-2,000 PSI during hard braking) pushes one or more pistons inside the caliper outward, forcing the brake pads against the spinning rotor. Floating calipers (most common on passenger vehicles) have a single piston on the inboard side — when the piston pushes the inner pad against the rotor, the caliper body slides on guide pins to pull the outer pad against the opposite side of the rotor. Fixed calipers (found on performance vehicles) have pistons on both sides and don’t slide, providing more even pad wear and better braking feel but at higher cost and complexity.

Brake caliper problems typically manifest as the vehicle pulling to one side during braking, uneven brake pad wear (one pad worn significantly more than the other on the same caliper), a burning smell from one wheel after driving, a wheel that’s noticeably hotter than the others, or a dragging sensation while driving. The most common failure is a seized or sticking caliper piston caused by corrosion, torn piston dust boot allowing moisture intrusion, or degraded brake fluid that has absorbed moisture. Sticking caliper slide pins (on floating calipers) are equally common — corroded or dried-out pins prevent the caliper from sliding freely, causing the outer pad to wear unevenly or not contact the rotor at all. DIYers should inspect slide pins during every brake job, cleaning and applying high-temperature silicone brake grease to the pins and their bores. Check piston dust boots for tears, and test the piston by attempting to compress it with a C-clamp — if it doesn’t retract smoothly or requires excessive force, the caliper should be rebuilt or replaced. Always replace calipers in pairs (both fronts or both rears) to maintain balanced braking.