Brake problem - sticking

[adciocca]

Good day guys. I have a serious problem. I searched the archives with no answer to this problem.

It started off being that the brakes would stick and heat up to the point that the ATE fluid would boil, hence no brakes. I changed my brake bomb, I rebuilt all four calipers, installed new pads and rotors and I still have the brakes sticking. My next move before buying a brake master cylinder is to replace the "BRAKE PRESSURE DIFFERENTIAL SWITCH p/n 34331150922" Does anyone have any suggestions?

When the car is cold, the brakes work perfectly. Brake pedal feel is tight. When the car is in a flat surface, I throw the car in "N" and the car freely rolls back and forth. After I drive it for about 5 miles, I start seeing my MPG drop and an awful smell of cooking brake pads. If I tap the brakes repeatedly, the brakes do not recover. Of course the pedal gets more spongy as the brakes build up heat and stick. Any help would be greatly appreciated. Car is decommissioned until I can resolve this.

Great thanks in advance.

Antonio
Thanks,
Antonio

1991 BMW 850i (black-USA)

[Dusty21]

Had a similiar problem with a '90 535i I bought 12 years ago it was 8 years old and I don't think the brake fluid was ever changed.

Turned out the brake lines were clogged. Almost impossible to
bleed the brakes, but after several attempts, and standing hard on
the brake pedal, the crud shot out...

No problems since, I flush the brakes every 2 years.

[adciocca]

You know what....now that you mention this, when I bled my brakes with the pressure pump, the fluid was not coming out in a stream like i thought it should. I'll re-bleed my brakes, but this time I'll get my wife to press the pedal. I'll try this next weekend when I can work on my car.

Thanks for the suggestion.
Thanks,
Antonio

1991 BMW 850i (black-USA)

[Steve L. in the ATL]

Hey antonio, How's things. Haven't seen you on the board for a min.

Steve L. in the ATL
1995 840 CI

[adciocca]

Doing great, but some glitches. Trying to get this cleared up so I can drive again.
Thanks,
Antonio

1991 BMW 850i (black-USA)

[Steve L. in the ATL]

sounds good. glad to see you back.
Steve L. in the ATL
1995 840 CI

[JB007]

I took mine to be bled by machine at dealer ($110), still a little spongy but I do have the single popt brakes. you could tap the brake lines to get air out and bleed several times but Antonio I think you have clogged lines/bleed nipples. Which brakes are sticking?

[KUANTINGS]

The sticking brake is the real paXX iX the A$$!! It wil ruin the fun when you drive the 8 and had you worry every time you drive.

I have the same prolblem last year, and after almost changed every brake parts(exclude calipers)to find out it was the brake master cylinder! I am 95% sure new MC will cure your symptom and you can use E32 MC as replacement part, the Dim is 1 or 2mm smaller but save a lot $$ on parts. It will feel softer when you brake but I kind like it.
After you slove the sticking brake remember to check if the brake disk wrap or not. my front brake brembo disk has been wrap because the heat caused by sticking brake.

Good luck and keep us posted, Kuan

[adciocca]

I think all four are sticking, that's why I think it's the MC as well. All 4 disks are piping hot to where even the rim is hot. I changed almost everything except the costly ones. Now I should be getting the MC and trying that. I will keep everyone updated...thanks for the help.
Thanks,
Antonio

1991 BMW 850i (black-USA)

[chromeowner]

the brake booster? If so, when you take it apart this time, please note the position of the 10mm actuator rod that runs between the booster and the MC. There's an end with square shoulders at the reduced diameter and an end with beveled shoulders. The beveled end goes into the booster. There have been a couple of reports recently of brakes binding coincidental to rebuilding the booster and I'm trying to sort out the situation.

More info on the booster:



http://bmw8.us/Brake%20Booster%20Rebuild.htm

Brake booster rebuild

[ADCiocca]

I did fix the problem for my brakes that were sticking. It turns out that the brake master cylinder was the problem. I did install a new unit as we all discussed from the E32 model. The discussion was that the E32 MC has a smaller in diameter piston and makes the pedal feel softer. Without any calculations on my behalf, I can tell you that there is a noticeable difference between the two. I suspect a reduction of pedal stiffness by 15-20%.

It works, don't get me wrong. My brakes don't overheat and my MPG increased, but I do not like the difference. I prefer the stiffer pedal feel.

I am now looking to see if I can find the E31 rebuild kit for the MC. Is there a place that rebuild old E31 MC? In any case, I am having my parents contact my friends in Italy to see if they can find it. I will report when they do.

[ADCiocca]

I did not rebuild the booster. AS it turns out, the MC was the culprit. I did look into the booster. There is a part seems like a spacer that aligns the MC and the booster. This spacer has a notch on the bottom of it. It looks like a drainage port to me. The piston that come out of the booster is rounded at the end. Does this help?

[chromeowner]

twitchy mechanism inside, 2 bore diameters, brake cups stretched over fragile metal frames, long 4mm screws held in with Loctite. You have to drill a hole in the rear piston skirt just to get the parts out with a pull hook. I was going to make a kit for sale, won't do it after looking.

[ADCiocca]

So basically scrap the old unit. If you drill a hole in the back, there will be a leak in the future. Is there a rebuild kit for the E32 MC? I can't see them being different except for maybe the internal piston diameters.

[chromeowner]

The piston diameter is everything. The e31 brakes are already soft;the thing to find is a MC one size larger, not smaller.

[ADCiocca]

My dad is hitting up my old Ferrari contacts to see if they know anything about a rebuild kit for the ATE MC. If I find one, I'll try it out.

[Cowiesbmw850i]

Have you found the Problem ?? I have the same year with exactly the same problem !!!!
Any help would be greatly appreaciated !

[email protected]

Thanks !!!

Chris

[adciocca]

The answer is yes. It did fix the problem.