High-Pitch Whine

[rdm05z4]

Pirish .. Really you had to go there.. This is why I try to avoid the BMW parts counter at all costs.!!! Never know what you might see!!!!

[Ewazix]

I'm glad you seem to have narrowed it down to the booster diaphragm, as I said at the outset your symptoms were as expected.

Nobody is going to say it's OK to drive with an under performing brake booster, if it failed completely you will have unassisted brakes and you will not stop in time, guaranteed. Truth is that a complete booster failure is rare, but as the leak gets worse your brake pedal may start to feel more solid which is the next warning after noises. Here in the UK knowingly driving with defective brakes that cause a fatal for example, will get you serious jail time, personally I'd rather have my pants pulled down at the BMW parts counter than in the jail shower block.

Fair point, thanks for all your help!

No problem (excuse the Brit' humour ).

I would double check the booster one way valve before committing to a replacement booster unit, a simple inspection and blow/suck test will tell if it's operating OK.

I've fitted a used servo booster from a breaker before on other cars I've owned and not had a problem which is obviously a lot less expensive, but would probably go for an aftermarket item at about half the cost of the BMW unit e.g. from a maker like ATE who make components for BMW. https://www.rmeuropean.com/Products/343 ... -MFG4.aspx

You can find the part number on Real OEM here https://www.realoem.com/bmw/enUS/showpa ... Id=34_1291


Good luck sorting it