Brake problem....HELP!!

[mgdisco]

I just replaced the brake booster and MC on my 95 540i. My problem is that after 3-5 minutes of driving the brakes start locking down. I am talking full lock down. Anyone ever see or hear of anything like this? Need help badly! Thank you.

[Ross]

You probably have the rod into the master cyl. improperly adjusted.
If the piston in the cyl doesn't retract all the way uncovering the ports to the resevoir ther is no place for fluid to flow back.
As your brakes generate heat the fluid expands with nowhere to go except puhing out the pistons in the calipers causing the brakes to drag generating mor heat etc. etc.

[mgdisco]

Is there any markings or anything to let me know what the correct adjustment is??

[Kalevera]

Were the ABS valves purged of air after the master was replaced? This typically has to be done with a good diagnostic computer -- I haven't done this kind of work without one, but I imagine it would be quite difficult to get all of the air out of the system without firing the pump.

Why were the parts replaced to begin with? I've never seen a failed 540 brake booster, except on a car that'd been in an accident.

If the brakes were hanging prior to the replacement and this was an attempt at fixing it....I've seen three cars, a '94 540, '98 (?) M Z3 coupe, '98 M3/4/5 do the same thing to a lesser degree, with no known fix -- theory was that the abs control unit or pump itself were faulty, but exchange with good working parts didn't resolve the issue. From what I recall, they all use the same ABS system.


best, whit

[mgdisco]

My MC was leaking fluid badly and I had NO brakes what so ever. I replaced it first had a great pedal feel but still no brakes. So apart I take it again to replace the booster after replacing booster and bleeding system three times, great pedal and great breaks for about 5 minutes then its lockdown.