what the heck causes death wobble? now i own 2 vehicles with it. my 05 cummins dodge has it and ive been chasin it for a while and now my 90 xj is doin it! i know the previous owner went all through the front end with all new parts recently. any help might save a life!

 

If your parts are good, fresh, tight, your steering damper is good, your track bar is tight, and you have wobble. then alignment.
No more than 1/16 toe in. You can't change the camber on your XJ (not easily), you probably need more caster. A good web site with great expanation and easy to follow process is "GoJeep.com" google it, a realy nice XJ build, lots of other ideas. I can get it in the operating ballpark at home with my jack stands and a ball of string and couple of measure tapes and a third hand.
If I have made radical changes (parts are good shape) the Pro alignment shop in town does a great job same day for $65