Ok here is my problem, after installing a 4.5 RE lift with upper and lower control arms, and quite a bit if wheeling if I'm going up a hill in 2 wheel drive it sounds like something knocking hard on the floor pan. If I'm sitting still at a stop sign and accelerate slow or fast i have the same sound. once i put it into 4 wheel drive the sound goes away no matter how i accelerate. any ideas on what this could be? by the way its a 98 sport 4.0, there are no sounds while just sitting still idling, only upon acceleration. thanks in advance for your help!!

 

Bad ujoints, bad outer bearings, or chipped ring gear. Is the knocking the speed of the driveline (fast) or the speed of the tires (much slower).

 

Check your tranny mount, could be twisting a little in 2wd, but in 4wd with both twisting it might not do it. Also look for some kind of marks being left behind from whats hitting

 

Mine is my motor mounts. I have the new ones sitting in the back seat.

 

I'm also having a similar problem. My noises started after i installed a t case drop. While i was installing, the jack supporting the crossmember failed and it was left hanging on its own. Would the mount be worn out or would it just be loose? Or both?

 

Check mounts and U joints.

Tcase drops are especially hard on mounts as they force them to twist.

 

Thanks for all of the info guys I will be checking all of these things tomorrow!

 

Did this knocking problem ever get resolved? I know its been awhile.
I have a 2001 xj with 4.5" lift which has the same knocking under acceleration but only turning right????
The noise is similar to that of a worn drive shaft on a front wheel drive, but sounds like its coming from the rear, "a rapid knock,knock,knock that stops after a few seconds?
If it was uj's, surly this would happen during left and straight acceleration also?
Any thoughts?
Cheers.