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Join Date: Sep 2019
Posts: 1
BMW Roundel BMW 645 Brake mystery

I have a very unusual problem with my 645 brakes in that they start dragging as operating temperature of the car rises.
This problem has gotten worse over the summer. When the car is cool and you apply the brakes they release properly, but at it warms up under the hood, sometimes the brakes don't fully release. It can be from a slight drag to almost as if they are fully applied. The strange thing is the brakes will release if you lift up hard on the brake pedal from underneath with your foot, even though it does not feel as if the brake pedal is moving.
My local independent mechanic has just changed the fluid suspecting contamination but that has not fixed it. He has found that if the car is left to idle from cold to operating temperature there is a buildup of pressure in the brake system to about 200 with no pressure applied on the pedal. Both the vacuum pump and the brake booster were changed in the last 1 1/2 years. Do you have any suggestions?

Old 09-23-2019, 10:59 AM
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Join Date: Sep 2019
Location: Perth, Western Australia
Posts: 1
New return spring(s) and seals for the master cylinder. Check the return/recuperation ports for debris. Check the pedal stop/adjustment and pivot for correct operation.

Old 09-26-2019, 07:04 PM
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