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00' 3.8L Hissing (Vacuum) Noise when braking...


jfl330
04-24-2006, 12:10 PM
We have had this issues for years, thought I would post up and see if anyone else has been down this road.

When you step on the brake pedal when going slow, you hear a hissing noise that you can almost modulate with foot pressure on the brake pedal.

Had the intake manifold gaskets replaced a few years ago, did not change anything.

Any thoughts?

wiswind
04-24-2006, 07:08 PM
One thing to check is the vaccum hose that goes from the back of the upper intake manifold to the brake "power module". The power module is the drum thing that the master cylinder is mounted to.
In my case, I recently found that the vaccum hose was pushed onto the upper intake manifold, but that the clamp was not positioned forward to clamp onto the neck of the nipple that the hose mounts to.
This can cause a vaccum leak.
Check that hose at both ends.......
Also is possible that it has a crack or hole in it.

The only other thing that I can think of is a leak developing inside the power brake "power module".

Does this happen when the vehicle is in PARK, at idle?
If so, you could check it out in your driveway, In PARK, parking brake set, at idle..hood up.. Have someone step on the brake while you listen under the hood.

Blue Bowtie
04-24-2006, 10:14 PM
If you're hearing it more notably in the interior, the power booster is probably on the way out. There is a silencer pad that should eliminate the normal air noise from brake application, but if the noise continues even after the pedal stops moving, you may have a new power booster in your future.

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