Just got done installing my 4.5 in rc short arm lift on my 2000 xj. Everything went good and there is only minimal vibe noise. So I am happy with the outcome, but there is one noise I am not sure what it is. It only happens when I am going like 40mph then I let off the gas and coast, when I put my foot back on th gas very lightly there is a noise in the back near my rear diff. It sounds like a slapping/grinding noise. When I step a little harder it goes away. The only thing I could think of is maybe the u joints? Does this sound like it could be the problem? If it is do I need to get them replaced right away or would they be ok for a while? Thanks

 

Sounds like rear ds u-joints. They'll get tore up quickly with the new angle causing them to bind so I would replace them soon. Did you do a tcase drop at all, shim the rear axle, or do an sye? Until you fix the cause (pinion-to-driveshaft angle), you'll just keep chewing through them.

 

I have shims, tc drop. Did not think it would be a problem. Could it be they. Are just old and the new angle is just messing them up.

 

So if I have shims and tc drop why would they be making that noise. The angle does not appear to be that bad. Maybe they needed replaced anyway.

 

If they've been in for a while then they've developed a wear pattern. Even a small change in angle can cause them to bind due to that wear pattern. Definitely sounds like you just need new ones.

 

Also remember whenever you put something new next to older parts, the older parts tend to not keep up with the newer ones.

 

Mine does this too. I'm gonna try u joints. Soon lol

 

Thanks alot guys you really helped me out.

 

Here are some pics of my u joints. Tell me what you guys think.

http://img26.imageshack.us/i/20110902071249.jpg/
http://img594.imageshack.us/i/20110902071305.jpg/
http://img685.imageshack.us/i/20110902071347.jpg/
http://img163.imageshack.us/i/20110902071327.jpg/

 

front pinion is a little low, rear looks ok though it should be lower unless you get an SYE. In any case, how the joint look from the outside doesnt necessarily reflect how they look on the inside

 

Sorry could u point out the u joints!!

 

So do you think. The noise I am getting is probably just from them being old and now it has a new wear pattern to fallow?

 

^ This is probably the answer. Put in new U-joints and then let us know if that fixes it or not.

 

I also have this problem! interested in what fixes it!