On Fri, 11 Jul 2008 23:59:21 -0700 (PDT), wrote:

I have some Gerdes master cylinders that were given to me years ago
which I am just now planning on using. Don't know much about them,
but was wondering if it wouldn't be prudent to have them be rebuilt
( overhauled ) before I use them, since they've been on the shelf for
so long. Is it actually possible to have them be overhauled and would
it be cost effective to do so? Thanks

Neal

Neal you have a gem there in your hands.they are one of the neatest
little pieces of aviation kit ever invented.

the aircraft brake fluid in them, the red stuff, is not hydroscopic so
it never absorbs moisture. the innards of your master cylinders should
be in absolutely pristine condition. they may need a flush out to
remove accumulated crap but the worst you should find is worn o-rings.

in each side of your brake system there are 3 o-rings. 2 in the master
cylinder and 1 in the wheel puck.
the master cylinder has a feature known as a free piston. this piston
has one o-ring that makes the side seal. in the face of the pushrod is
another tiny o-ring that seals against the face of the free piston
when you apply toe brake to push the piston down.
these are the easiest things in the world to recondition if they are
old but in good nick.
buy the proper o-rings from your local aviation shop, my last ones
were under $aus20 for the 6 o-rings.

getting most of them apart involves taking the circlip out of the top.
this is a standard circlip and is about 3,000 times as stiff as it
needs to be. once you get that out without damaging anything the rest
is easy.
just slide it all apart. take the old o-rings out and put in the new
ones and your "reconditioning" is done. just remember to lube up the
new rings in brake fluid before putting them in position to prevent
nicking them.
reassemble, refill with red aviation brake fluid (actually an
automatic transmission fluid) and you will have pristine reconditioned
master cylinders.

you can find an exploded view of the innards of your cylinders in the
middle of an old cessna repair manual. in the 100 series cessna manual
it is figure 5-23 on page 5-37. it gives a perfect idea of how it all
goes together.

......actually I'm lying. they've been on the shelf for so long now
they'll be totally stuffed. mate I'll take them off your hands for $15
and I'll pay the express postage :-) :-) :-)

Stealth (you have a gem there) Pilot