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Brakes lock and don't release on 525i E28

 
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dmitry_oz
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PostPosted: Tue Oct 02, 2001 7:19 pm    Post subject: Brakes lock and don't release on 525i E28 Reply with quote

Hi guys,

It really drives me crazy :((
When I drive in traffic with frequent starts/stops breaks lock and don't release !
It causes brake disks/pads overheating !
Also when it happens I hardly can push brake pedal ! If I stop a car and cool it down for 15-20 mins this problem go away and I can drive again.
If no traffic - no problem.

Any suggestions ?

With regards,
Dmitry
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charliesmith



Joined: 07 Jul 2001
Posts: 738
Location: Dallas, Texas

PostPosted: Fri Oct 05, 2001 2:22 am    Post subject: Brakes lock and don't release on 525i E28 Reply with quote

Dmitry,

Do ALL the wheels lock up and drag when hot? If you have a hydraulic jack handy, toss it in the trunk. Drive/stop until symptoms reoccur. Pull over and jack the front end up and spin each wheel. Repeat for the rear. If ALL wheels are dragging, the master cylinder is most likely at fault. If only front or only rears drag, probably the proportioning valve is at fault. You HAVE been changing the brake fluid annually haven't you?

I agree with turbo too. Calipers with black scummy mud in them can seize when hot. It's the slight flexing action of the brake caliper piston "O" ring when brake pressure is released that actually pulls the piston (and the brake pads) back a few thousandths of an inch from the rotor.

Two possibilities. When brake pedal is released, either brake pressure isn't actually going to zero OR the caliper piston(s) isn't/aren't withdrawing in the bore allowing pads to drag.
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