Thumping sound from front of jeep

One of the rare times i turn off my radio I hear this thumping noise. Not a knick-knock noise a kinda deep thumping noise. Its under the hood in dash area. I think its a vacuum issue. If I hold down the brakes and turn on the ac the brakes mush up a bit. It speeds up as I hit the gas and when i hit a certain speed it stops until i slow down. I'm pretty sure its not a lifter because it will go away and come back. No Idea.

Any thoughts?

Climb underneath and check all of the rear driveshaft universal joints for free play. Also check the transmission mount. Try to pull the back of the transmission from side to side.

sounds like drivetrain to me too.

Brake gets mushy when you turn on ACC's. and you hear a thump.

It could be the diaphragm in the brake booster on it's way out

It could also be as simple as the vacuum line going to the booster being cracked

The directional valve for the line going to the booster may be faulty.

have some one pump the brakes a few time wile the jeep is running and listen around the booster.

I've seen and heard this one before.

winterbeater said:

Climb underneath and check all of the rear driveshaft universal joints for free play. Also check the transmission mount. Try to pull the back of the transmission from side to side.

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I'll give it a try. I don't think its that because it coming from in front of the front passenger seat. Not to mention the little vac valve/pump thingy on top of the vac can clicks. Quite loud at times. Enough to hear over the engine. I'll crawl under it tomorrow.I'll report when i find out more.

run it for a minute...shut it off.dont touch it for a few min.
Then with it off,
see if your brakes still have enough vacuum reserve when you depress them.