Brake caliper

How it works

The brake caliper is the part that clamps the pads against the disc. Inside, one or more pistons are pushed by brake fluid when you apply the brake; seals around each piston pull it back slightly when you release, freeing the disc. There are opposed-piston (fixed) calipers, used on most road and sports bikes, and floating calipers with one or two pistons on one side that slide on pins. Over time, dirt, road salt and moisture foul the pistons and pins: the caliper sticks, a pad drags constantly, the disc gets hot and the bike feels held back. Conversely, a piston that does not extend properly gives weak or uneven braking. A caliper can be cleaned, rebuilt with a seal and piston kit, or replaced. It is a safety-critical part: a rebuild requires care, a proper bleed and correct tightening torques.

Maintenance tips

• ✓Clean the caliper and the area around the pistons regularly, especially after winter or salted roads.
• ✓If a wheel turns stiffly by hand or a disc is unusually hot after a ride, suspect a sticking caliper.
• ✓On a floating caliper, check that it slides freely on its pins and that the boots are intact.
• ✓A rebuild (seal kit, pistons) always ends with a full bleed using fresh fluid.
• ✓Torque the caliper mounting bolts to the manual's value; if in doubt, leave the job to a professional.