Bad Brake Booster?

First the specs:
1985 XJ with the 2.8 V6
Manual transmission
About 131,XXX miles on it...all original under the hood except clutch master and carburator
New Brakes about 2 months ago

Now the situation:

I am getting a whooshing noise coming out of the brake pedal. More specifically, there is a plastic diaphram that covers what appears to be a pushrod that leads through the firewall and into the brake booster.

The whooshing noise goes away when the brake pedal is depressed, but when I am not on the brakes it makes that noise...similar to the sound of leaking air.

When I turn off the Jeep, it lasts for about 5 seconds then silences.

That makes me think that it is a vacuum problem, but the vacuum lines that I see running to the brake booster are all fine.

Could my brake booster be failing? If so, it is an easy/cheap replacement? Is there any options for replacing...I seem to recall people swapping in ZJ boosters.

Any help or direction would be appreciated.

Cottontail said:

I am getting a whooshing noise coming out of the brake pedal. More specifically, there is a plastic diaphram that covers what appears to be a pushrod that leads through the firewall and into the brake booster.

The whooshing noise goes away when the brake pedal is depressed, but when I am not on the brakes it makes that noise...similar to the sound of leaking air.

Click to expand...

When I bought my Xj, i had the exact same thing. Replaced the booster and it was fixed. It was fast, easy, and i dont remember it being terribly expensive.

Sounds almost certainly like a booster. Here's a quick check. Run the engine for a minute and then turn it off. Don't touch the pedal. Go have a cup of coffee or a beer or something, then come back. Don't be in a hurry. Now with the engine still off, push down on the brake pedal. If you still have boost (you'll feel the soft pedal, and hear a kind of sighing noise), you're doing all right. If you don't (hard springy pedal) you need a new booster. A good booster should hold vacuum overnight or longer, so if you've lost boost within this short a time, it's definitely toast.

Had this problem in a 77 Dodge pickup, the booster. Check to see if it has vaccuum reserve after a few minutes or just disconnect and plug the vacuum line to the booster. Run the engine and see if the noise goes away with the line plugged. This problem can be caused by failing master cylider seals, brake fluid leaks into the booster (and engine), eats the rubber in the booster If the truck is consuming brake fluid its not normal, both items need replaced I used a salvage part from a 93 truck to fix the 77 dodge. Gotta love Mopar interchangeability. Be sure to bench bleed the new master cylinder.