How to... change brake caliper seals - 2

2: Seals

There are two seals on each piston: an inner fluid seal, and an outer dust seal. The outer is to try and keep dirt out, and the inner one has two jobs: it holds the fluid inside, obviously, but it also keeps the piston in the right place. When you pull the brake lever, the fluid pushes the piston out and clamps the pads onto the disc. When you release it though, you need the piston to come back a little bit so the brakes let off. The rubber seal does this job: it distorts a little bit under pressure as the piston moves out, then pulls it back again a small amount when the pressure is released. As the pads wear, the seals let the pistonsĀ  gradually move out further and further, taking up the extra clearance.

If your brakes are binding or sticking on, it could be down to the seals getting old, dirty, or losing their flexibility. The pistons don't get pulled back properly, and the brake pads stay on the discs.

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