Been dealing with a pretty gnarly vibration when accelerating from a stop, especially on a hill. Very noticeable and can feel it. Had one guy tell me that it was because of the 4.5in lift I have which was pulling the drive shaft back and separating the teeth. I already have the crossmember drop kit installed. Curious if any of you guys have had this problem and how you fixed it. I know one solution would be the slip-yoke eliminator but not trying to spend that kind of money...

 

You may not have a choice.

If the u-joints are all good, and the bearings in the rear axle are good, it likely is the driveshaft.

It's not separating the teeth tho, or you wouldn't move, but it has moved the wear points between the teeth in the driveshaft & on the output of the tcase, it has changed the load on the output shaft bearing in the tcase, and it has changed the range of motion/wear on the u-joints, so all of that is now having to 'wear' back in, and that is likely the noise/vibration you feel.

 

have you thought about a hack and tap instead of a whole SYE kit? that's a tall lift without a SYE of some kind

 

^ Correct.
The stock 2-joint rear driveshaft is not compatible with 4.5" lift. Its operating angle has been exceeded. Must be replaced with a 3-joint driveshaft (double cardon) like what is on the front of XJ.

 

Drivelines are all about angles. Everything is supposed to be as close to parallel as possible to aboid vibrations. When you lift the vehicle the axles stay at the same position and this changes those angles. The rotational cycle of the shaft is now oblong instead of a circle. A double cardan shaft and SYE bring in another universal joint that for steep angles and gives the parallel angle back to the output shaft.