Funny you should ask about the brake pistons, I just went through the excercise
on Friday...
I used a bike tire pump to remove the pistons. I adapted the pump outlet to the
male brake line fitting with various hose bits and adapters. It required about
50 PSI to get them moving. I put a plate of 1/4" thick Aluminum into the slot
where the rotor normally lives. This is because the less-sticky piston comes
out first, and once it pops out, you can't apply pressure to the other one; the
plate prevents either piston from coming all the way out. I wanted them both
out for powder-coating the calipers; if you don't mind one piston at a time
it's not an issue.
You've got to wiggle them out from there. If you're replacing the pistons
anyway as part of a rebuild you can be more creative in urging them out since
you don't have to worry about damaging the surfaces. I thought I was being
gentle but I wiggled too hard against the casting and nicked the piston enough
to suggest replacing the pistons (which I hoped to salvage, although there was
some slight pitting evident).
I was fool enough to separate the caliper halves (not before consulting Dave at
Winner's Circle). There's no mystery in there, just a square-section elastomer
seal. The trickery is the self-locking threads. Different suppliers use
different methods to lock the threads, from a suspicious-looking plastic patch
on the screw to an EDM'd slot and swaged threads on the screw. The swaged
threads undoubtedly do some damage to the tapped holes each time they're run in
and out.
The screws took 65-70 ft-lbs to remove. I have not found any installation
torque specs - does anyone know? It's a 7/16"-20 thread, and Dave at WC
suggested 50-55 ft-lbs to install, without the knowledge that I'd be quoting
him repeatedly on the internet of course...
Separating the caliper halve makes it a lot easier to remove the pistons. The
piston in the "bridge" is much more accessible than the one in the "base," so
you may wan to try pushing the "base" piston further out than the "bridge"
piston by biasing the dummy rotor towards the bridge side.
- GT (another RPI alum)
>>>
Date: Fri, 17 Jan 2003 08:43:04 -0500
From "Chris King" <cbking at alum.rpi.edu>
Subject: Couple of tech questions
Hi all.
Couple of questions (1500 Midget):
I have a new set of pistons on order, and I believe they come complete
with new wrist pins. Can I use the new pins with the old con rods (and
bearings), or should I ue the old pins matched with their bearings with
the new pistons (assuming, st this point, the bearings are OK - I
haven't checked yet)?
I've got a 3 stone hone to break the glaze on the bores. Do I need to
lubricate the stones when using, or should they be used dry?
Is there an easy way to remove brake caliper pistons from their bores
without using compressed air?
My cam came back from TS Imported yesterday, and looks good! I also
ordered a 2-2-1 header from him, and that looks cool too. I'll be checking
the fit on the head soon with the SU manifold.
- -=Chris
Chris King - cbking@alum.rpi.edu
http://mywebpages.comcast.net/kvcbk/
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