Dana is correct....(more) (archive)

Dana is correct. If you have mushy brakes, and the brakes are as effective as normal (i.e., you still stop on a dime like all BMWs are supposed to, just that it takes longer pedal travel and there is very little initial bite from the pedal), I'd flush and refill the Power Steering system with new ATF first. The ATF, which gives power assist, just like any fluid gets old and gets less effective. Also, the PS filter can clog which will give weird behavior in the hydraulic system - change that as well.

If the problem still persists, and you don't have the brake light coming on (which indicates brake bomb), then it's the booster that has failed (usually the internal seals start leaking). The reason is because you're not getting the power assist, thus you have longer pedal travel, but the same effectiveness in the braking. There are tests for the booster and bomb in the Bentley. Old ATF won't be as effective as well, that is why changing that first can give a better indication if it's the booster or just the fluid. (The symptoms will return in a short amount of time if it's the booster - even with new fluid, so you will definitely find out soon enough if it's the fluid or booster).

If you have mushy brakes, and the brakes are LESS effective, then you should replace the master cylinder, ASAP. But before, check the calipers to make sure nothing more serious has happened anywhere there (leaking lines, blown seals, etc) - remove the pads and check the pistons too - as well as the pads and rotors and rotors themselves. If all the components at the wheels are fine, then start on the master cylinder.

Christopher Graff

Try flushing the PS fluid any cleaning or changing the PS filter. I just went through a master cylinder change to improve my mushy pedal, and it improved only after the PS fluid flush. I think your brake booster may be weak internally.
The bleeding should be slow at the rear, but a bit faster at the front.

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