Brake Problems

#1

As part of my Spec E30 build, I attempted to install SS brake lines. The fronts were no problem, and are now installed, but I could never get the old rubber lines separated from the steel lines on the rear. I finally gave up on that and focused on getting the engine installed and running (accomplished last night!) and just left the rears alone until I can get the car on a lift to get better access to the inner rear lines. During the process, I did take the rubber lines off the rear calipers.

My buddy and I bled the brakes thoroughly before trying to start the car. Everything seemed good. Upon starting the car last night, however, the brakes pedal immediately felt spongy. During the test drive, the brakes were spongy and had to be pumped to get any braking. After a few slow laps around the neighborhood, we took it back in the garage and checked the brakes. One fitting was slightly loose on the right front, but everything else seemed OK. We then bled the brakes again and everything seemed OK until we got to the left front. Tons of air and grungy fluid came out. We bled until that was resolved and clean fluid was flowing.

On another test drive this morning, the brakes were the same as last night. Spongy and had to be pumped to get any braking. I haven’t had a chance to check anything further yet.

Any idea what could be causing this? Air in the ABS unit? Faulty master cylinder? Could pump-bleeding the brakes have caused the seals in the master cylinder to fail? (I saw a reference to that on a forum).

Any help would be appreciated.

#2

If another bleed doesn’t find anything interesting like obvious air and grunge, then I’d suspect the master cylinder.

You did enough of this during the day (or in a garage) to detect any kind of brake fluid leak, correct?

I have also read that a a dieing MC can be killed during the bleed/flush process by pushing that brake pedal down too far.

#3

If you bled them that thoroughly you shouldn’t have had that much air and old fluid come out. Did you bleed them in the right rear, left rear, right front, left front order? And did the MC at any time run out of fluid while bleeding?
The air could have also just come from the right front loose fitting maybe?

#4

We bled the brakes both times RR/LR/RF/LF. The mc never ran out of fluid during the bleeding. We bled the brakes in a well-lit garage and saw no obvious signs of a broken line. I inspected all the connections and re-tightened them just in case. As I said, the only slightly loose fitting I found was on the right front where the line goes into the caliper. There was some fluid on the caliper and had dripped a little on the wheel rim. I wouldn’t think that would let in enough air to cause this problem, especially in the left front.

#5

If the fluids clear it must be in the mc. I don’t think a booster problem would cause a spongy pedal.

John

#6

Decided to do one more bleed before springing for a new master cylinder. This time got a bunch of air out of the right front after about the third set of pumps. Very odd. Got clean fluid after the first two set of pumps. Not sure how the air got that far into the system, but since getting it out, the brakes are fine.

For what it is worth, the Bentley manual says that when bleeding brakes on a car with
ABS, you should pump the pedal a dozen times before opening the bleeder valve. Did that this time, although I’m not sure that’s what did the trick.

Now I can try to find out why the ABS isn’t working.

#7

The most common failure for the ABS is the over voltage relay, which is attached to the top of the ABS computer under the Drivers Side Dash. They run about $25 or you can take the one on the car apart and resolder.

#8

With my E30, I could not get a good feeling pedal by manually pumping.

I find that the Power Bleeder does a better job and it’s easier (also a one man job). I usually pump it up to somewhere between 15-20 lbs.

Also, after the major bleeding, activating the ABS and then bleeding just little bit more seems to help in firming up the feel.

YMMV.