paul cormier

My S4's brake light stays on for a while after startup. I am also having an odd pulsing at the pedal, sometimes at freeway speeds, sometimes at slow speeds. It is intermittent, so I am not sure it is warped rotors or not. I have Porsche 993 front caliper/Euro A8 rotor upgrade.

I have searched and read quite a bit about our brake systems. And, acting on Fred Munro's article <a href="http://www.elektro.com/~audi/audi/hydraulic.html" target="_top">here</a>, I was testing the servo in step two.

First I disconnected the line going back to the Mineral Oil reservoir, and found oil to be constantly coming back through it with the engine off.

<center><img src="http://pictureposter.audiworld.com/4377/dscn1314.jpg"></center>

More than a steady drip, not a pour. Then I re-connected it, not sure that it was the right one, and then re-started the engine to make sure the Bomb (pressure accumulator) was still pressurized, and my brake light out. It was. I turned the engine OFF. Then, I disconnected the return line at the top of the servo.

<center><img src="http://pictureposter.audiworld.com/4377/dscn1310.jpg"></center>

I then watched a similar steady more-than-a-drip coming out of the Servo. So, I'm assuming it is bad... YES?

Also, after reading one of popdemonic's <a href="https://forums.audiworld.com/s4s6/msgs/162820.phtml" target="_top">notes</a> on the Servo, I started the car with the upper return line still disconnected from the servo. It quickly pumped a cup of fluid out of the servo and on my garage floor. I haven't seen this recommended anywhere else, and maybe I misunderstood him? Maybe my servo is REALLY toasted?

paul cormier

BTW: Having rotors turned tomorrow to make sure that isn't the problem.

popdemonic

His car was just the brake pedal pulsating all the times.He borrowed me a pump, Accumulator,Brake servo. Finally,The problem wasn't fixed.Finally, he found the cause is from the loosen clamp on the feed line to the steering pump,So when the pump is cycling.
the pump will drool up the oil with some air bubble into the system cause the brake pedal stay pulsated.another case is,If the feed line stayed higher the fluid level in the reservoir that should be ended up with the same result.

From your case what I remember is there should not have much of the oil out from the return line if you haven't applied on the brake pedal.
Anyway,Keep the servo as your last suspect.believe me.Mostly,If your brake servo failure,there will be the fluid leak under your footwell.

paul cormier

I'll check the pedal for fluid drips. I'll also check all the lines to the pump as you recommend.

I also suspect J-hose leakage as the bolt on the underside of the Bomb is always weeping, I think fluid trails down the hose. I'll be sending it to the famed Seattle House of Hose for a rebuild soon, as a precautionary measure.

The rotors are turned, and I'll put them on tonight. I'll repost with results.

popdemonic

I'll try to help you figure out your cause.

paul cormier

And the pulsing seems to be gone... along with the squeaky brakes. I think when I initially installed the Big Reds I was over aggressive with my brake pad bedding technique and that I warped the rotors (Euro A8 rotors from ECS tuning) a bit and glazed the pads. I still have not inspected the brake pedal for fluid, but I'll do that today. I should also get to try out the high speed pulsing that I've seen in the past. Will post again soon with that feedback.