Originally Posted by
dabac
I've never had a caliper apart yet, so I can't say what's lurking inside. Only obvious thing on mine is a really flimsy spring that push the pads apart.
I don't think there is one though. Since the pads self-adjust on wear, and the pistons are simply pushed back on pad replacement, I'm rather struggling to visualize how one would work.
It's the piston seal that retracts the piston. The seal, which most often is a square cross section, sits loosely in a recess in the caliper bore but fits tightly around the piston. As the piston moves out of the caliper body it drags the rubber seal with it, deforming it. When the pressure is released, the seal springs back to its original shape, pulling the piston back a small amount.
The seal can only deform so much, so if the piston has to move further to press the pad onto the disc, it slides in the seal. The piston will always be pushed out until the pad touches the rotor, but will only spring back a fixed amount. That's what makes it self-adjusting. The spring is there to push the pads apart when the pistons retract.
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Ragnar