# new master, now hissing from booster (b5 passat 1.8t)



## MyCarIsRed (Aug 9, 2004)

the brake master went bad on my passat, so i replaced it. that in itself wasn't very fun, but now after running the car and building up pressure in the brake system, when i turn the car off, i get a hissing noise coming from what i assume to be the booster. it sounds like it's blowing off excess pressure but it doesn't seem like it should be doing that. any ideas?


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## Andromeda451 (Jan 6, 2006)

*Pressure in brake servo?*

Driver, 

There is no pressure in the brake servo unit. The most common problem is that the O ring that seals the gap or interface between the servo and the master cylinder was not installed or was/is damaged. This results in vacuum leakdown after shutdown. 

Good luck.


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## MyCarIsRed (Aug 9, 2004)

that was kinda my thought. but would that cause a difference in brake pedal feel? it's at the shop now, hoping they can figure it out.:facepalm:


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## GTijoejoe (Oct 6, 2001)

feeling would be reduction in boost assist since the vacuum level in the booster would be reduced.


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## MyCarIsRed (Aug 9, 2004)

is it possible to rtv the seal rather than pull it all apart to replace it? i don't like to do things the wrong way, so if this comes across being a hack job, just shout.


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## GTijoejoe (Oct 6, 2001)

Its possible but you would have to take the MC back off the booster to do it correctly.... and by then you could just check the seal and replace it.... a lil RTV wouldn't hurt I guess :sly:


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