Resolution of clutch problem

Joel Skousen Joel at
Sun Apr 19 17:17:19 PDT 2009

Thanks for all the suggestions on my clutch problem.  To review, after a 
long drive in my 88 5Ktq the clutch pedal was not coming all the way up , 
but otherwise acted normal throughout the early part of the trip.  Turns out 
it was a sticking upper seal on the master cylinder plunger---not the flared 
lipped part of the upper seal that does the actual sealing, but the base of 
that same seal, which is slightly larger in diameter than the plunger 
itself--too large in my case.  I don't know if it swells over time, or 
whether the barrel gets dry.

I disassembled the master cylinder, and inserted the plunger in backwards to 
test the fit of the upper seal base--lots of binding pressure.  If I lubed 
it with brake fluid and held it just right it would slide, but with some 
effort.  It appears that after driving a while and actuating the clutch many 
times, the upper part of the barrel begins to wipe away all the brake fluid 
and the seal begins to bind--overcoming the internal spring pressure as well 
as the reverse pressure of the clutch pressure plate.  I put the plunger on 
my late and sanded down the diameter of this upper seal base (not the flared 
part) so it had less pressure in the barrel.  Now it works much easier. I 
then reassemble it and put some brake fluid at the top of the plunger to 
make sure it didn't go dry.  Works great now.

Joel Skousen
88 5ktq Avant plus other assorted Audis

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