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Re: Brake Problem - Stuck MC!

At 06:03 PM 12/17/96 CDT, you wrote:
> Jad.Duncan@GAT.COM (Jad Duncan) asked:
>> I have an '89 90 Quattra that is a great car exept for a weird brake 
>> problem.  After driving the car for about 10 miles on the freeway without 
>> using the brakes, they begin to apply themselves.  The pedal becomes rock 
>> hard, does not move and all four wheels seems to start dragging evenly.  A 
>> hard jab of the pedal releases everything and the car is fine.  The ABS 
>> switch has no effect on the problem and the brake system checks out fine by 
>> the dealer and an Audi specialist.
>Jad - working from memory - a problem VERY similar to this was 
>discussed some months ago.  If I recall correctly, the problem was 
>traced to a faulty master cylinder.  

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.

 - Mitch Loescher, PhD