Topic: What makes the caliper retract?

[robdrobd]

What makes the caliper retract after the brake has been applied?

[the architect]

It never really retracts - it just quits applying pressure once you release the lever.  So, there's always some minimal (almost imperceptible, when it's adjusted correctly) amount of drag on the rotor from the brake pads.  It's the same in cars.

But this makes me ask the question . . . .  Why are you asking? 

[robdrobd]

I was just tearing my caliper apart and it made me wonder. Makes sense now

[MikeJW]

As you squeeze the brake lever, hydraulic pressure behind the piston forces it out, pressing the pad against the rotor. As the piston moves out, it distorts the rubber ring seal in the chamber. When you release the brake lever, there is no more pressure against the piston and the seal tries to resume its natural shape which pulls the piston back. When brake lines are not regularly flushed, water & crud builds up in the system, the piston corrodes and the seal eventually loses some elasticity and can no longer retract the piston and brake drag usually occurs.

[Duke McDukiedook]

Unless you have a phenolic piston of course...