Missed this one yesterday, but in scanning the replies, I only noticed
various prying and air-pressure options recommended. Prying can easily
damage parts, and maybe you. Air pressure can make a piston into a missile,
or at least smash a finger or two if/when the piston pops loose. Besides,
the pressure available with air is pretty small compared to typical brake
system pressures, and it may not be enough There's a good and SAFE way to
remove stuck pistons.
Disconnect the brake hose from the steel brake line at the chassis bracket,
and take the caliper off, with the hose still in the caliper. Run the
locknut down the threads all the way onto the brake hose. Get a grease gun
(full of cheap grease) and unscrew whatever outlet fitting is threaded into
it. Match the threads of the hose and grease gun - if it's a US-made grease
gun they SHOULD match, but if you don't have a US-made grease gun, maybe
not. When you have a matching grease gun, thread the brake hose into the
grease gun and begin pumping grease into the caliper. Soon you will see one
or both pistons moving. Just before the first one pops out, stop it from
moving farther with a "C"-clamp, and continue pumping grease till the other
piston gets to the same point, then carefully remove both pistons - they
should by now easily slip out by hand.
This method has the advantage of being more powerful (many hundreds to well
over 1,000 PSI of pressure available from most grease guns) and safe -
grease is essentially non-compressible, so when you stop pumping, there's no
accumulated pressure - nothing will explode.
Karl Vacek
'66 TR4A - IRS
'64 Amphicar
'16 Ford T Touring
'46 Piper J-3 Cub
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