'89 200TQ Brake Problem - Stuck MC?(was: urgent help needed...)

[I6941tb@aol.com]

In a message dated 96-12-17 22:09:21 EST, loescher@neosoft.com (Mitch
Loescher) writes:

> Al is right.  It is a sticking master cylinder.  I had my 87 5000SQ do the
>  same thing about a year ago.  From your description, I'd say you should
just
>  replace the MC (can't/shouldn't rebuild because corrosion causes the
>  problem), but if you want to check, get the car to exhibit the symptoms
>  however you can, then just crack open the brake lines at the MC.  If fluid
>  shoots out (a mL or 2) and the brakes release, then the MC was the culprit
>  for sure.  When I did this test, my car had gotten so bad that the brakes
>  would overheat and the steering wheel would shimmy.  When I did the brake
>  line test, I had been leaning with my knees against the front bumper and
>  when the brakes released the car rolled back so freely, I about lost my
>  balance!  Front brakes were fine though (runout when not overheating was
>  ok).  Damn Audi brakes are tough!
>  Good luck, not that you need it, I'm sure the MC is your problem.

This looks like a ticket to solving my problem. Here's the latest:

Tonight I drove to my buddy's house in N. NJ, about 70mi away. On the way
there I drove rather rapidly, trying to make the appointment on time. After
about 10 mi and a few energetic stops the car started to lose power as if the
brakes were dragging. The pedal's travel length and feel had changed also. It
would now show very little resistance for the first 30-40mm of travel after
which would become hard as a proverbial rock. It also hissed while travelling
those 30-40mm. The brakes themselves lost their effectiveness by about 50%.

I was prepaired, though, this time I had a 2 ton hydrolic jack in the trunk.
I immediately pulled in the gas station and ran, not walked to jack up the
rear end of the car by a centre of the rear subframe in order to hang out
both rear wheels before the brake sys cools down and releases the binding
wheels.

Here's the story: both rear wheels were very difficult to rotate by hand as
if the e-brake was up by 1 tooth (incidently, the e-brake is new and properly
adjusted). They were equally hot and smelled the same. No amount of kicking
the brake pedal or pulling up and releasing the e-brake seemed to unlock the
rear wheels.

The whole thing was over in 10 minutes after the wheels cooled down a bit.
Both rotated freely, the pedal acted normal (grabbed after the first 5mm of
free travel) and I was on my merry way shortly after.

It seems that whatever is causing the brakes to bind, workes on both rear
brakes simultaneously.

I suspected the proportioning valve, since it has one brake line coming in
and one line coming out, terminating with a T which distributes the brake
pressure to rear wheels.

Now, after reading this post, I have started to suspect the MC. After all,
the MC and the Brake Servo are the only original (non-rebuilt) hydrolic parts
on my car with a build date of 5/88!

I should have checked the front wheels also and performed a MC lines release
test. Oh well, tomorrow is another day.
Does it sound like I have a sticking MC? Can it be a sticking Brake Servo
instead? Any input is sincerely appreciated. Hate to drive through Canada
with the dragging brakes, especially with them european gasoline prices! Or,
worse yet, what if one day rear brakes would lock up on me at high speed?! I
guess no quattro would save my butt of being peeled off the guard rail later.

Igor Kessel