Okay 99 XJ, 125,000 Miles, 4x4, heavy duty leafs, nothing crazy......At 30 MPH on the nose, my Cherokee has this shake/knock. Got under the Jeep lefted the rear up turn the truck on. Looked at the driver shaft while it was spinning and didn't seem like the driveshaft was bent. Put the truck back down and started twisting and pulling on the driveshaft, no problems there either pretty solid. I know most are going to say u-joints but it doesn't seem like it. I just replaced the brakes about 5 months ago, just got new stock tires and rims from a friend cuz I thought I had a bad rim. New UJ on the front, new Timken bearings on the front, and still the knocking is there, only when I apply the gas does it show up. coasting down the road doesn't really show the vibration as much. Any question ask, I appreciate the input though....needs some ideas.

 

Check your tranny and TC mounts.How are your shocks, what about rear sway bar mounts? Are the u-bolts tight?Motor mounts to.

 

just did the leaf springs so i know those are tight along with the rear sway bars. where exactly are the tranny mount and the t-case mounts??? I've heard this before but everything under my jeep seems solid so I'm thinking it was the UJ but i appreciate the input. I'm just wondering what else it could be. keep em coming gentlemen

 

when was the last time you had an alignment?

 

haven't done one since i bought the thing.

 

but i don't think that has anything to do with it since i only get the vibes at highway speeds or I'm on the gas, coasting I don't really get the vibes.

 

Do you get the shudder over light bumps too?
Im not familiar with the suspension set-up on these cars, but if it was a toyota MR2 i would tell you its the ball joints.

 

Might try having tire balance possible tire problem - have had this happen tread separation from tire at higher speeds.

 

I would check the trac bar bolt at the axel tube I have heard of that being an issue. I had a similar prob but it was at around 40 mph replaced the steering stabilizer and prob solved.

 

Thats interesting. Could you describe where that is, I'm not sure if I know what your talking about. But that would make sense, old steering stabilizer and get the shake. The only thing is it feel like it's under my seat. Now maybe that isn't a good way to figure out where the vibes are coming from. If you could show me a pic, worth a thousand words. Thanks guys

 

Here's a weird one, how's your exhaust? any black marks from a leak. that is another thing that can make noise and disappear when you let off the gas.

 

You know I thought of that but said no it wouldn't be that much, I'm actually gettign the exhaust manifold replaced tomorrow. I don't have the time to do it myself right now since I'm up here in Maine in school. My exhaust is getting replaced though so we will see what happens and I'll keep you guys posted. Thanks again.