From:
markrock_REMOVE_451666_THIS_@yahoo.com
John:
Duke's right. A master cylinder that has been lying around for years
is undoubtedly junk, but he failed to explain why. There are, it
seems, two reasons. First, it has likely seen years of service
and has worn and/or become corroded inside during that time. Second,
and more importantly for a unit that has been off the car and not
sealed, it has undoubtedly suffered accelerated corrosion of the
piston bore since being removed.
"Why would that be?" you ask. Easy. Brake fluid is hygroscopic, it
attracts moisture. If the master cylinder has been lying around with
the lines removed, or even with the short lines still attached, but
with the openings uncapped, then the moisture in the air, which moves
in and out a tiny amount with changes in temperature and in
barometric pressure, moves into the area where a film of brake fluid
can be found. The moisture quickly contaminates that film, and the
contamination migrates along the film deep inside the caliper where
it ultimately reaches the piston bore and begins to corrode it.
Duke offers the option of rebuilding the master cylinder. Here he
and I part company. Cheap as I am, I would not rebuild a master
cylinder, or even a wheel cylinder. In my younger days I rebuilt
both, and can recall repeatedly rebuilding Corvette calipers, ones
that are notorious for corroding and for which the "fix" is to
install stainless steel sleeves. My experiences told me that the
results were short lived, and not worth the savings over purchasing
new equipment. Since then I have learned that I might have obtained
longer-lasting results with some specialized hones from Flex-Hone to
put a much finer finish on the bores, but I didn't have that tool
then, and it would not be cost effective today.
Take Duke's first suggestion. Buy a new unit. Or one that has been
professionally rebuilt. Take all your cores with you to the
parts store, order a new unit, and use it to pick which core to turn
in. Just remember that in 76 there was a running change in the
design of the unit, so the reservoir on what you have might not match
the reservoir on what you will get--i.e. they will look very
different but will be functionally identical.
Mark
[This is message #10600 by user markrock on Yahoo! Group Cosworth Vegas:
http://groups.yahoo.com/group/cosworthvegas ]