e46 bmw. when driving the car, you can apply the brakes a few times. however if you have applied the brakes say 4 or 5 times, the pedal goes rock hard. the only way to get a soft pedal again (and there fore brakes) is to rev the engine. after a few blips the pedal is soft again. does this indicate an air leak somewhere? eg the brake servo? how can i test or fix it?
I would say its the pipe from the brave master servo to the inlet/vacuum supply. Inspect it for leaks/splits.
Run the car for a few seconds and then stop it , pump the brakes and see how many assisted pumps you get then do the same but stout it and leave for a minute between trying it , the valve in the servo line should hold vacumn in the servo , there could be a split in the line but it would normally cause high idle etc or poor running . The vac pipe will just pull out of the servo so run the motor ans stop it wait a min then pull the pipe and there should be vacumn still there , then run the motor and put our thumb over the end and see how good the vac is
thanks will try in a few days whwn get chance. worth mentioning that the vacuum pump was removed and resealed as was leaking oil. will check how much vacuum its producing, how can you tell if its enough vacuum though?
no its a petrol. bmw have a vacuum pump on the engine, then you have a pipe coming from it to the brake servo
