[cutthroatkid]

Ok first off anybody who knows me on here knows I usually ask a ton of questions about my projects bit this is about my dd.Its a 2 nd gen dodge ram with the 360 awhile back the hvac started acting funny replaced every vac line I could find still no fix,next found out my plenum is leaking so I orderd the parts to fix but I haven't yet&today I go to run some errands&when I push my brakes I hear a hissing like when the booster goes bad.Ive checked the booster&cylinder &there ok.Now Im wondering could my leaking plenum gasket be causing these problems?When I bought my mustang it did the same thing hissing when applying brakes but booster was ok...ended up being a rusted out reservoir.So input?Could it be the plenum?

[T-bucket23]

Bad booster

[cutthroatkid]

But Ive tested the booster&its holding vacuum.Ive turned it off&pumped brakes till hard held&started &it went slowly to ground&Ive started turned ofd&removed valve&heard the woosh.Like I said on my mustang it did the exact same thing&I replaced the booster&ot still did it ended up being a keak somewhere else that was causing the hiss@brakes&when I fixed that leak it fixed the hissing@brakes.Thats why Im wondering if its the plenum leak since it causes a vacuum leak in the crank case.

[sbchevfreak]

Just because it hold vacuum, does not mean it won't leak when the brakes are applies. Put shortly, there is a valve system on the booster that allows atmospheric pressure into the rear chamber when the brakes are applied. This is the ``boosting`` effect. There is a vacuum and an atmospheric valve, and if you hear hissing when applying brakes, this valve assembly is shot.

[cutthroatkid]

Originally Posted by sbchevfreak

Just because it hold vacuum, does not mean it won't leak when the brakes are applies. Put shortly, there is a valve system on the booster that allows atmospheric pressure into the rear chamber when the brakes are applied. This is the ``boosting`` effect. There is a vacuum and an atmospheric valve, and if you hear hissing when applying brakes, this valve assembly is shot.

I got ya...not sure if this makes a difference or not but maybe my choice of words wasnt too good...its not reallyva hiss like a sucking or a leak more like when u push down on a kids bicycle air pump like shhw shhw sorry if thats a crappy explanation.