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Hi guys, I'd like to test my conclusions on my brake problems.
Car is 1992 S4.
* Brake boost unavailable at start up about 50% of the time
* Brake light stays on for 30-60 seconds after releasing e-brake
after car has sit for more than 1 hour (This symptom has existed
for several years)
* Sometimes after sitting, brake pedal depresses in jerky motions,
instead of smooth travel. Smooth travel returns after hydraulic
pressure builds up.
* Pentosin and brake fluid levels OK.
* Bomb OK (passes bomb test consistently)
* I cracked open low-pressure (return) line from brake
servo. Lots of fluid comes out when engine idling.
(A lister told me this should be only a few drops for
a good servo.)
* Pulled master cylinder from front of servo. Everything looked
clean and normal inside servo housing. No leaking fluid. (Not
sure exactly what I was looking for.)
* Bad servo. Allows hydraulic pressure stored by bomb to leak
through servo. When car is started, it takes a while for full
hydraulic pressure to build up and operate the inlet pressure
switch on the servo, which is connect to the brake light. Perhaps
some pressure even needs to build up in the return line before the
switch is triggered. This could also explain why I have never been
very happy with the brake pedal feel in this car. I loved the
pedal feel in my old 87 5000CSTQ (very solid), and was surprise
when I bought the S4 (used) in the difference.
* It looks easy. Two bolts to remove MC. Disconnect brake pedal
linkage. Four nuts (inside of firewall) to remove servo. R&R.
Anyone BTDT that can warn me of any gotchas? Does this diagnosis
Fort Collins, CO