4 wheel alignments are only if its independent rear suspension which your don't have,Where is the vibration coming from the front of the rear of the jeep?Next time it happens shift it in to neutral on the trans see if it stops right then or only when you slow down.If it stop when you pull it in to neutral its driveline vibration if it stays then its suspension.

 

He definitely would benefit from sye and cv shaft. Go ahead and take off your front drive shaft. You might have a bad u joint somewhere or a shaft out of balance. Go ahead and get alignment and make sure tires are balanced.

 

I'll try that on my way to the tire shop. I'm sure it's the driveline. I do believe the vibes are in the rear end.

 

So i left my shims in, and on the way to the shop and back I had no vibes... I'm baffled how they were there last night, but not there today.

Regardless I took out my shims today. Now I have very minor vibes at random times. Maybe it's just me hearing my new MTs since I'm not used to hearing them.

Either way, thanks for the help guys. I appreciate it.

 

Could be, and no the xj has leaf springs in the rear (you prob know haha) but that centers the axle so can't really align that

 

We still don't know how your u-joints are. They are the most likely culprit. Also, check your motor mounts and transmission mount. Look for cracks or deterioration. I say this because I fixed a vine issue I had, replaced my mounts, and had new vibes due to the height of the new rubber. Plus I'm all for preventative maintenance.

 

I checked my u joints, they seem solid. I'll check the mounts as soon as I get a chance.

 

I didn't read everything else cause this has been covered millions of times, but I'd put the tcase drop on for now (not the shims), if that doesn't get it drivable, then throw the shims on to see if they help. Then order a hack n' tap sye from iron rock offroad (think they still may offer a refurbished drive shaft too) and if not go get the front drive shaft out of a 4x4 jeep cherokee in the junk yard. And install.