alightman

My '93 S4, which I had given to my daughter, had the brakes stop working. Seems to be a little boost on first application, but pedal very hard, stoping slowly with great pressure. Slight vibration in the pedal. Worked it hard, all 4 discs warm. I did the requisite sta, good info on replacing the various parts, but not for diagnoses. I suspect the bomb, but shouldn't the system have pressure when the engine is running? Could it be plugged, it's been years since a fluid flush. Brake indicator is on, power steering is fine. Any thoughts would be greatly appreciated, I'd like to keep the old girl alive, she's been very good to me.

UrS4boy

Search for a test on the bomb, i.e. how many pumps with the engine off until the pedal gets real hard. From the SJM Autotecknik website:

"One test for the accumulator, is to run the engine for a few minutes, turn off the engine, and then pump the brake pedal until the pedal feels hard, (no more power assist). Normally with a good, working brake accumulator, this test takes 25-35 pumps on the pedal before the pedal gets hard. If the pedal gets hard with only a few pumps on the pedal, the brake accumulator is defective and should be replaced. "

SJM Autotechnik, Audi Technical Service Repair Information

alightman

I read Scott's post, very informative. Mine has no assist period, even with the engine running, pedal hard from the first application. That makes me think it's not the bomb.

UrS4boy

I think it is the bomb (pressure accumulator for you readers from Home Land Security). However, *IF* it isn't the bomb then it is the one side of the tandem power steering/power brake pump and you either need to replace it or rebuild it.

Replacement: HERE

Rebuild: http://12v.org/urs/GrahamTsPSPBPumpStripDownDIY.pdf

alightman

Thanks for the info, I assumed the pump was good from the fact I had steering, didn't know it was tandem. I'll check for pressure going in and out of the bomb, that should tell the tale.

UrS4boy

Note: I just fixed the photo issue in the PS/PB Re & Re link when/if you need that.

Replacement: HERE