My brakes locked up.

911/914gary · 03-07-2005, 12:18 PM

I posted this on the BMW site but this group seems to have the largest knowledge base. Can anyone help?

The brakes on my 525 (2002 model year) have locked up. My wife had driven the car about 80 miles that day. Then suddenly the brakes started to drag, the peddle travel tightened up and eventually locked. The ABS warning light went off. The brakes got so hot they smoked. I let the brakes cool and took it for a test run. In about a mile the condition re-occurred. I recycled the ECU by disconnecting the battery for a minute. Took the car far another test drive and nothing occurred for several miles.

It is evident that the brakes and sensors need to be replaced. The rotors need to be checked for warpage. The fluid should be flushed. All of that I can take care of. But what is wrong with the brake system. I don’t know where to start trouble shooting this. Has any one heard of brakes locking up like this before?

Thanks

Superman · 03-07-2005, 12:42 PM

I've had brakes act like this twice. Most recently, it was a handbrake cable that was so bunged up with crud that the cable did not return. The gunk between the cable and sheath was preventing the cable from returning. The return spring is not strong.

Previously, I had a vehicle with a hydraulic brake mechanism. Apparently, if the brake pedal is adjusted without enough free play, then the master cylinder piston does not retract far enough to exchange fluid with the reservoir. When you push the brake pedal, the piston goes past the port that allows reservoir fluid to drop down into the cylinder bore. If the piston does not retract far enough to allow the reservoir fluid to come into the MC bore, then it also does not allow MC pressure to bleed up into the reservoir. It becomes a "closed" system and just a little heat then can create enough pressure to be applying the brakes all the time. Actually, now that I think about it, it was a hydraulic CLUTCH mechanism, not brakes. But the principle is the same.

Early_S_Man · 03-07-2005, 01:02 PM

Gary,

That car is too new for any of the traditional causes to be valid ... unless it has been used heavily in the rust belt where salt is used on the roads in the winter! In CA ... I think it has to be a corrosion problem on the ABS sensors or cables.

Any warranty left on the poor car???