e39 sinking brake pedal

[sixcyl320i]

03 540iA
Replaced all rotors and pads to cure pulse. Found the rf caliper to be sticking. Opened caliper bleeders to depress calipers. Depressed pedal according to all-data to replace caliper. Flushed system, ran abs pump and precharge pump according to all-data. The fluid in the system was dark and had never been done before. Did the pedal pump 12+ times for fronts as all data and the autologic stated. Put wheels back on and noticed pedal would sink to floor if you pushed it hard. (only while running) compared pedal height to 2 other e39s and found it to be an inch or more lower than the others. I rebled the calipers and still got the same result. Pinched off front caliper hoses and the pedal is great feeling. So i rebled the entire system following procedure again, thinking i screwed up. Tapped calipers with hammers and no air. NEVER got air. Now has 2 more new (napa) calipers and has been bled through 6-8 times very thouroghly. I even tried just flushing with the machine and bleeding brakes manually after the first 2 or so failed attempts. I know the pedal isnt the firmest of all cars, but this feels like a GM pickup pedal. The car stops great and has no pull but the pedal feels like crap. Its the bosses car and neither him nor I like how the pedal feels compared to before.

Anyone have any advice or had a similar problem in the past?

Thanks!

Matt

[thejlevie]

The brake pedal sinking to the floor under constant pressure says that either there is a leak or the master cylinder is bad. Since I think you'd have noticed a leak by now, the next step would be to replace the master cylinder. When you pull the master cylinder off the booster use a rag on a wire (or similar) to see if there is brake fluid in the booster from a leaking seal in the master. If there is, replace the booster. Brake fluid in contact with the diaphragm in the booster will cause early failure of the booster.

[sixcyl320i]

What I dont get is when the front brake hoses are pinched off with clamps is that the pedal gets firm and does not sink down. Its actually up higher than all other cars by 3/4 of an inch and will not sink if you stand on the pedal with bohemoth pressure. The pedal is good and firm when the car isnt running. the problem is only when the car is running. sorry if i didnt mention that before. any other input Jim?