Brakes sticking

[lennon]

I'm messing with an e30 whose brakes are sticking on a bit in the front. The car sat for atleast a few years. I believe it's due to clogged lines not allowing the pressure to return to the master cylinder. I don't think it's the master because disconnecting the line at the master doesn't release the pressure. Disconnecting the bleeders and soft line releases the pressure, and disconnecting where the hard lines go into the ABS unit releases the pressure. So, I think the clog is in that hard line (both sides?!) from the wheel well to the ABS unit. I already replaced both soft lines at the wheels, because those were pretty clogged. Calipers and master are off of another good working car.

What do you guys think?

[lennon]

bump for help!

[jizo]

Im having the same problem!!! I just decided to flush out the system. There was actually MUD comming out of those lines. I was told that you have to flush out the system every 2 years. Who does that? Anyway, Mine are still sticking abit but will flush out system again. After flush, it has gotten alot better. If after flush still....Im gonna do MC and see where it takes me. Mind you....Im still driving around in the car...LOL

[lennon]

The brakes on my cars get flushed, but this car sat for a long time I believe. Either way, all the lines have been flushed now.

Before, I thought it was holding pressure somewhere in the lines before the master, but now it seems to be at the master. Any time the brakes stick (still only fronts), cracking open the line for the fronts at the master will release the brakes. It's obvious the fluid is trying to return to the master cylinder and can't. This master cylinder is from a functioning brake system on another e30, and I have tried another. I've inspected it out of the car and cleaned it. It seems to retract just fine and was pretty clean inside, ports not obstructed.

I have checked the adjustment on the booster rod, and disconnecting that from the pedal will not release the brakes, so that's not the problem.

I can drive the car around for an hour and have no problems, or I might drive it a few minutes and they will stick on. When bleeding, the fluid comes out strong as normal on all 4 corners. Pedal feels great, never sinks to the floor or anything. Next step is to buy a new master? The booster also seems to be leaking air. There's a hissing sometimes when pressing the pedal. This couldn't be related to the brakes sticking, could it?

[jlevie]

A bad booster could be preventing the master cylinder from fully extending.

[lennon]

This master seems to be having trouble "retracting" if anything. Could a brake booster cause that? If so, how? When the brakes are stuck, I have disconnected the brake pedal and the booster rod is all the way retracted. I have also disconnected the vacuum line to the booster and won't release the brakes. Separate issue I guess...

Though it is like the pedal is being slightly depressed, even though it isn't. There's always a little bit of pressure in the system up front. Maybe the master isn't coming back completely every time.

[jlevie]

This master seems to be having trouble "retracting" if anything. Could a brake booster cause that? If so, how? When the brakes are stuck, I have disconnected the brake pedal and the booster rod is all the way retracted. I have also disconnected the vacuum line to the booster and won't release the brakes. Separate issue I guess...

Though it is like the pedal is being slightly depressed, even though it isn't. There's always a little bit of pressure in the system up front. Maybe the master isn't coming back completely every time.

The clevis that connects to the brake pedal isn't a part of the master cylinder. So the master cylinder may not be fully extending even though the clevis is returning.

[lennon]

The clevis that connects to the brake pedal isn't a part of the master cylinder. So the master cylinder may not be fully extending even though the clevis is returning.

yes i know, and that's exactly what i'm thinking.

[lennon]

man this shit is pissing me off. new master, still does it. lines seem fine. without fail, every time i drive it and heat up the brakes, they stick. disconnecting booster has no effect. only thing that works is undoing the "front" line from the master, fluid comes out, then it's fine till a few more stops.

what is it?!

[z31maniac]

And you're positive it's not the rusty, old calipers?

[nando]

yeah, likely it's the pistons seized up inside the caliper housings. time for a rebuild kit - cheap and easy.

[lennon]

Tthe calipers are off of one of my working cars, they are not rusted at all and move quite smoothly.

I THINK I have figured out the problem, but not the reason or the solution.

The rod from the booster to actuate the master seems to be too long. Or rather, the recess in the master cylinder rod is not deep enough. Some dimensions/depth are not right. When mounting the master, I now see that the last few threads actually start pushing in on the master. It would need roughly a 1/8" spacer in between the master and the booster. I have the O-ring/gasket that goes there. This is not related to the adjustment/threads on the booster rod, the pedal is not interfering whatsoever, and is disconnected currently.

The original master came on the car, as it came to me and in all this troubleshooting/new master, carquest only asked if it was Girling or Ate (it was Ate). After looking for myself, I see there are Girling and Ate, but also both a "up to May 87" and "from 87 on". This car is an '88.


What is the difference in those masters? If they are different dimensions that would explain my problem.

EDIT:

After looking at the parts catalog some more, I see that the boosters are the same for early and late model. This makes me think that even if my master was from the wrong year, it should still work with this booster. Hmm...

[lennon]

And you're positive it's not the rusty, old calipers?

yeah, likely it's the pistons seized up inside the caliper housings. time for a rebuild kit - cheap and easy.

guys, i wish it was that easy. if you saw the situation in person, you'd see it couldn't be the calipers. if it was stuck calipers, they wouldn't release when i crack open the bleed screw/any front fitting. the front lines are slightly pressurized, that's all that's holding the calipers.

[lennon]

man. found this thread: http://www.bmw2002faq.com/component/...15dc48a9f065a/

shims? gotta check that out.

EDIT:

Checked out another e30 booster I have here at home, and there is indeed a shim/washer under the removable (news to me) rounded tip of the business end of the booster rod. This one here is about 1mm thick. Maybe the booster on the problem e30 (not here at home) has a much thicker washer or something. It would have to be atleast 5x this thick. Hopefully that is the problem.

[jlevie]

The booster can be ATE or Girling and you must use the matching master cylinder. If the car has an ATE master and Girling booster or vice versa you may have found the cause.