I've been following this board since buying my 7 a year ago here in the Land Down Under and have enjoyed and benefitted tremendously from your knowledge.

Now I have a reason to post a message: My brakes seize up, especially in city driving conditions (ie frequent starts & stops) but my mechanic can't find the fault. First, he thought it was the pressure accumulator. But changing it solved nothing.

What do I mean by 'seizing up'? Well, it's like the brake pedal becomes 'hard' and I can't depress it all the way down like normal. But the brakes still work.

I don't get this problem when driving in the suburbs with light traffic. It only acts up after frequent starts & stops. So as you can imagine, this makes it harder for the mechanic to troubleshoot.

I'm still driving the car now. But I'm worried one day it will just seize up completely and leave me with no brakes at all.

Does anyone know what I'm talking about? Can anyone tell me what is wrong or knows vaguely what is the likely problem? Any advice or suggestions will be much appreciated. My thanks in advance for taking the time to respond.

Tom
1985 735i
199k KM

First thing you need is a new mechanic, as diagonoses do not get any easier than this.
Second, your problem is most likely that either (a) the bomb (the pressure accumulator) which you have already ruled out, or (b) one or more of your brake calipers are hanging up, which means that they are not releasing the rotor when you take your foot off the brake. The pedal hardness comes because when you push on the pedal, one or more of the calipers have already extended (this is because they never released the rotor after the last application of the brakes) their respective pistons to grasp the rotor, and thus, your pedal travel is limited as if you were already stomping on the brakes. The fix is easy--look for the wheel or wheels that are the dirtiest or the hottest after a drive--seized calipers cause a lot of heat and brake dust obviously--and replace the sticking calipers and the rotors on that axle. Remember to change rotors and pads in axle sets; calipers can be changed individually. Good luck.