> What is holding the piston in the caliper? ...how does the piston then
> retract when the brakes are not applied?
There's a pin in the center of the cylinder. This pin grabs onto a
spring-loaded doohickey mounted in the center of the piston. As
the pads wear, the piston slides (with much resistance) further out
along the pin; the spring loading of this grabber gadget (technically
called he retractor mechanism) retracts the piston just a bit when the
brakes are released.
It is very important to respect this pin, as a) it holds the piston in
really, really tightly, and b) it makes it a bear to reassemble the unit.
You must get everything aligned dead on straight and press it together
while avoiding nicking the seal ring (hint: if you nick the seal, your
brakes will ultimately leak and fail).
You'll almost certainly need air or much more preferably hydraulic
pressure to pop the assembly apart. I've written about the procedure and
the dangers before. In brief, BE CAREFUL as when you apply air
pressure you're creating an almost-explosive device. When it pops it will
FLY if you don't contain it. Some people use an old master cylinder to
apply hydraulic pressure - much more controllable, but messy :-)
If the piston walls are pitted, chances are you won't get it to ever be
reliably leak-free.
For a more technical picture of how it goes together take a look at:
http://www.hyedracyl.com/images/d5.gif
-- John
John F Sandhoff sandhoff@csus.edu Sacramento, CA
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