When i press on my brakes when the engine is off, there is a hissing sound, from what i can tell it coming between the booster and the master cylinder at the bottom, is there a seal im missing between the booster and the cylinder that im missing or am i missing the rod seal on the cyilnder? or what??

thanks kyle

 

cheak the one way cheak valve. keeps booter pressur from going back.

 

After looking at the booster it apears that there is suppose to be a vent hole at the bottom, Some one wanna run a brake test for me? all you gotta do is pop you hood with the engine off and have a friend press on the brake, what im looking for is if you hear/feel and air escaping at the bottom of where the master cylinder meets the brake booster.

thanks kyle