[armanos]

Hi all,

I wanted to share my fix for the infamous hard brake pedal on BMW M47N2 engine.

So I got the hard brake pedal after the car sat overnight. First I thought the non-return valve in the booster was bad. So I removed it (after much work), tested it and it seemed to hold vacuum just fine. So I reinstalled it and greased the sealing ring with vacuum grease. This did not cure it.

I renewed the rubber vacuum lines to the EGR valve, as well as the O-ring on the plastic nipple on the main vacuum line that goes into to vacuum pump. Again, the pedal was still hard.

A was baffled. Then I checked the short rubber hose between the vacuum pump and the plastic main vacuum line (see the picture). It seemed somewhat loose, but not massively so. The rubber had dried out over the years and the clamps did not hold it tight any more.

So I installed two worm gear clamps in place of the factory clamps. At this point I was worried about the vacuum pump pulling in some air and overloading the PCV system, not about the hard brake pedal.

To my surprise, before starting the car on Monday morning after it sat over the weekend, my brake pedal was soft and easily depressed! Never had it hard once for months now.

Apparently, the main vacuum line should also hold some vacuum for the brake booster non-return valve to work as intended.

Also, do not forget the small rubber o-ring on the nipple (15x2 mm OD/thickness, fluoroelastomer o-rings can be bought on aliexpress or locally), on my car it was totally dried out when I renewed it.

In addition, now I can rest assured that the vacuum pump does not pull in excess air which eventually overloads the already problematic PCV filter on these engines.