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checked fluid too - not cause, but wouldn't help (archive)

[ Follow Ups ] [ 7-series (E32) Message Board ] [ Msg. Board FAQ ]

Posted by Max Fretter (NZ 87 735i) on April 04, 2001 at 14:05:21:

In Reply to: Re: ????why are my brakes on constantly???? posted by David F on April 04, 2001 at 10:57:12:

I don't know how often you relace the actual brake fluid, but that can be a problem too.. not the base cause, but old fluid with ANY water content in a "dragging shoe" (yes, I lnow they're pads, that's the term I grew up with!) situation to heat that fluid up will end up adding pressure as the water tries to boil in the calipers behind the pistons....

I only know this as I had a similar situation on a K100 BMW bike rear brake one time... over adjusted so the caliper dragged, only noticed when I started slowing down after a long highway ride. Eventually forced to stop as rear brake locked on, 5mm stainless rotor was a nice "blue"!! est abt 200C, took over 1/2 hr before I dared start flicking water at it GENTLY to aid sooling, it was that hot. Oh well.


Our symptoms are EXACTLY the same. Although it sounds like yours is worse. The rotors probably warped due to excessive heat from the draggin brakes. So, for sure, fix the dragging problem BEFORE you replace the pads/rotors.

I am going to check if I have an adjustable actuator rod/link from pedal to booster. If I do, I will adjust in some slack to eliminate this from the equation (i.e. booster not returning fully).

Yes, the pedal's returning to the normal position but the phenomenon is the same...different every time I get in. The interesting thing is that when the car is first started in the morning, the brakes work fine. It's only after driving for a while and it seems worse in stop and go traffic.

Coupled with the warped rotors, the car shakes violently when it hits just the right resonance at about 50mph. (already got the rotors and brakes ordered but want to get to the root of the problem before I stick them it).

It's going to be a learning experience since I've never done anything on brakes besides replacing rotors and pads.

Thanks for the advise. Keep me posted on your findings! I'll take a stab at your suggestions this weekend.


My 88 750 is starting to do the same thing after prolonged stop and go traffic. Some have suggested that the master cylinder is the problem. My pedal IS returning to the normal position. Is yours?

Since my problem is intermittant, I cannot perform the following, maybe you can:
1. Loosen master cylinder mounting bolts at brake booster. If brakes release, then I would suspect the booster is not returning. Check for pedal obstructions that would prevent the pedal from returning to normal position. Otherwise, suspect a faulty booster.
2. If no changer after step 1, then crack a pressure line or two. If brake(s) release then suspect a faulty master cylinder.

One interesting fact on my car is that the pedal never really feels the same from day to day or stop to stop. I really am leaning toward the master cylinder and possibly a weak accumulator.

And no....don't say because I'm pressing the brake pedal or the emergency brake is on :)

The brakes don't seem to want to retract back.

What could be causing this? Need help desperately!


1989 750iL

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