Some malfunction with auto hold could cause similar symptoms if the P brakes applied themselves but if they stopped you from freeway speed you would smell them.

Regarding the master cylinder nuts: if you get the locked up situation, you should be able to loosen them a little bit and it should relieve the pressure.

read some of the threads talking about the push rod being too long and adjusting it. It is exactly the symptoms you describe.

since the problem presented after replacing the master cylinder, it’s probably just a tolerance of manufacture issue.

you can confirm the booster is problem by disconnecting the vacuum line of course plug it with a screw or something and you just don’t have power brakes. You have to push really hard to stop the car, but the problem should go away.

there was a recent thread on XO where somebody had that problem and confirmed it that method


–awr–

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)