Whistling sound when releasing brakes

x-driver

x-driver

Active member
 Slovenia
Can anyone tell me what would be causing this whistle sound when I release the brake? If I press the brake pedal just slightly, the noise disappears immediatly. It then sometimes comes back immediatly when I release the brake while sometimes it doesn't come back for some time. See the video (turn the volume up).

 
Stick your head under the bonnet and have a listen near the vacuum booster. Probably a slight air leak where the pipe goes in (give it a wiggle.)
 
It's basicly impossible to hear the whistle in the engine bay when the engine is running. It can however be heard for some 10-20 seconds after engine turn off, but not always.
 
x-driver said:
It's basicly impossible to hear the whistle in the engine bay when the engine is running. It can however be heard for some 10-20 seconds after engine turn off, but not always.
Click to expand...
That definitely sounds like a vacuum dissipating. Air getting in somewhere.
 
Would a smoke test help here?
How to tell if the leak is inside the brake booster? Is a new one the only solution in such case?
 
Where the vacuum pipe goes into the booster is the most likely spot. Try reseating it.

However, it might be worth removing it to look for pinholes. Friend with an E91 found a rusty hole in the bottom of his that gave him just enough assistance for one good brake and then he was in his own until the vacuum had built back up .
 
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