In a message dated 96-10-03 13:04:26 EDT, you write:
<<
My problem is with the cylinders that the pistons fit into. There is some
rust on the cylinder walls (not much, but it is noticeable and I can feel it
with a fingernail), and there is a bit more rust on the area of the cylinder
that is just outside of the rubber dust seal gasket. I have tried to clean
this off as best as possible using only brake fluid per the Bentley, Haynes
and Autopress manuals, but it some of it remains. The other problem is that
I tried to fit the pistons back into the cylinders but no luck. They simply
will not go back in. Any help would be appreciated as to (1) what to do
about the rust and (2) how to force the pistons back into their respective
cylinders. >>
Ross-
You can clean up the inside of the caliper bore just about any way you want
(sandpaper etc, I use a brass "toothbrush") as long as you don't go to the
extreme of removing so much metal as to make the hole out of round. Basically
all the bore does is keep the piston straight and allow it to move in and out
freely. Be especially observant to remove any/all crud which has built up in
the o-ring groove. Also pay attention to the finish on the piston itself. Any
flacking or pitting on the piston will only tear the o-ring as it goes by, or
at least leak when asked to seal against the piston. If you have any
pitting/flaking, save yourself some grief and get a new piston now.
With the o-ring out of the caliper, the piston will be a close fit, but once
aligned should almost drop into the bore (this may take a little "rocking" of
the piston back and forth for alignment).
When you assemble the unit, remember that cleanliness is next to ...well
choose your own godhead. With the o-ring back into the caliper bore, apply
lots-o-brake-fluid to all the surfaces and gently rock the piston back and
forth while applying a light pressure to the piston. DO NOT FORCE IT IN. That
square o-ring works by grabbing the piston side as it goes by and deforming
itself enough to pull the pads back from the rotor when you release them, so
it will try to grab the piston as you are pushing it into the bore. BE
GENTLE. If the piston does not want to go in all the way, you may want to
release your pressure and actually pull the piston back out a bit in an
effort to keep the o-ring intact, then start again with the pressure/rocking
thing.
Good luck, hope this helps...
Nick in Nor Cal
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