^ Brake calipers are self-adjusting units. When brake fluid pressure is applied to the caliper piston, the seal ring in the caliper wall deforms slightly, allowing the piston to move out and engage the brakes. When brake fluid pressure is reduced, the seal ring returns to its original shape, pulling the piston back and disengaging the brakes.
As brake pads or rotors wear, the deformation of the seal ring reaches its limit and the piston actually slides out further before regaining a stable position again.
Brake fluid seeping or leaking from around the caliper piston is the result of a failed or damaged piston seal ring. A damaged seal ring is usually caused by corrosion, scoring, or pitting of the piston or caliper bore. The seal can be replaced separately, but a damaged piston will quickly damage the new seal. To remedy a leaking caliper piston seal and avoid future problems, complete replacement of the caliper is recommended.
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