Luis_M

I am now hearing a vacuum-leak hissing sound in the cabin which appears to be coming from near the brake pedal. This only occurs when I apply medium to hard force on the brake pedal. This stops when I let off the brakes. No sound with light pressure. I can only hear this when the car is stopped but this is probably because it is not very loud. The brakes seem to work fine, although brake fluid change is due. I cannot recall ever noticing this before. Any ideas? Impending booster failure?

Luis
1981 928S Euro 5sp

neilh

Hi, Luis - as you only really hear it when stopped, try unplugging the vacuum line to the booster, plug it ( on the engine side) and check it again. Otherwise, look for a vacuum line hanging down behind the brake pedal area that your are snagging with the pedal ( not sure if there is one, but maybe!)
If you want to take a ride over here to RB i'll help you check it out.
Neil.

jpitman2

Unusual that you can hear it well, but not unexpected. When you apply the brakes, the boos is supplied by atomospheric pressure reponding to vacuum (low pressure ) on the other side of the diaphragm in the booster. This air goes in through a filter around the pedal push rod, but usually its sound is drowned out by other noises. You might look along the pedal push rod and check that there is some sort of fabric/fibre filter at the booster entrance. If you get the car somewhere quiet, run the engine briefly to get vacuum, turn it off, then apply the brake it should be obvious.
jp 83 Euro S AT 53k