Hi all, I am in need of some advice. First issue, my '97 XJ started making a "clunking" sound at low speed when the gas is let off. Second issue is at speeds of say 5-55mph all is well, but once you hit 60-65mph the rear starts vibrating, pretty bad too.
The XJ has what I think is a 2-3inch lift on it from PO (I just got it and have been fixing it up) so I don't think its a driveline angle problem. I have replaced the following: motor mounts, tranny mount, U joints (they were good but I did it anyway) shocks, brakes, drums, new diff fluid front and rear, and I have run a few different sets of tires/wheels thinking that may be the problem. I also checked the U bolts and shackles but they are tight.
When I replaced the U joints I checked the rear pinion for play. There is none but it does move left and right (rotates) until it engages the ring gear. Seems like a lot but I never had a 8.25 before.
So, the big question is: repair or replace? Never rebuilt a rear before but I found a posi unit from an 8.25 on local CL and would love to put it in.
Any help/suggestions would be greatly appreciated.

 

I'm going to update this as I troubleshoot because I see quite a few threads online dealing with the same thing. Maybe this will help someone else.
I picked up a clean 8.25 at the local JY for $200. More than I wanted to spend but I couldn't find one locally for less. Went through 6 rears looking for a track loc, but no luck so I took the nicest one there.
I also ordered a SYE kit and new transfer case chain from CSE offroad. Little over $200 shipped for both.
The more I listen to the noises and vibrations, I am leaning towards the driveshaft/transfer case end. I am going to do those first before I swap the rear. I know my chain is stretched because there's a ton on slack so I figured I'll install a new chain with the kit. BTW it's not a hack and tap. Should have that done this weekend.

 

How many miles on your `97? Mine just turned 50K.

 

185,000. Other than this damn vibration, you'd never know it.

 

Driveline angle; mine does it. The angle may look close, but may not be close enough. I let off and get a "clunk/Grrr" from the rear. I think the angles are off just enough to make noise, and not chew up the u-joints. I'm doing a SYE in a few weeks, once I get the time as well.

 

Ok, installed my OMIX SYE this weekend. First off, the instructions suck, and the damn slip rings are a mother to work with. That aside, the interior was very clean, very few bits of metal, and once I got the hang of the slip rings it was not too bad. Installed the kit and new chain, reassembled, filled it with ATF, and re-installed. Took her for a test drive, and now the vibrations actually seem worse. On top of that, I am getting some new weird noises from the t-case. Sounds like the chain rattling in there and I'm having some binding on shifting from 4h to 4 low. The clunking in the rear is really noticeable now.
So, I am going to remove the t-case again and make sure I didn't screw something up on reassembly and install the new rear this weekend.

 

Ok, I discovered the e-brake cable was rubbing the driveshaft and was the noise I heard. The t-case has smoothed out and is shifting fine. It is leaking out of the front yoke after it sits for a few hours (no idea what that's all about). I think I'm getting there.