Hissing when applying brakes - '95 940
 

Whenever I hit the brakes in my car, you can hear a loud & steady hissing coming from the brake booster. If I give it some gas while holding the brake I loose all assisted braking. My question is, has anyone else experienced this, & is my brake booster failing or do I just have a massive vacuum leak?

Thanks for the help!

I did some thinking & reading about some other things, and I've been thinking it might be the vacuum check valve. If it is bad, there will be no vacuum reserve. The first time I press the pedal it's fine. Unless you pump it or hit the gas then it gets hard. So the check valve is going to be #1 on my list. Thoughts?

that and the vacuum hose itself.

update: I have not replaced that AC check valve yet. IDP lists 2 check valves: Vacuum check valve & a AC check valve so I'm not sure which I need. I've completely lost all power assisted braking. The hissing is worse now as well. The engine idles at about 1000 RPMs, drops & sputters when I apply the brakes(Park or N). I'm starting to think its the booster itself...

inspect the larger diameter vacuum hose that connects to the brake booster, and the right angle plastic fitting it connects to. probably need to replace one or both of these.

brake booster

yes, thats the name of the part. what about it?