Lorrel

Just started today. 94XJ 5spd. owned since new in Apr94. Have 65K miles. Stock engine, stock X-mission, stock clutch. 6" RE custom lift with 33x10.50x15 TA/KO's. 4.10 gears Have had lift, 33's, and 4.10's on for 10 years now, and everything is tight. No DW now and never had. All tires in good shape. Have Warn front locking hubs, and vibration occures whether locked or unlocked. This is while in 2wd, while driving on road, streets and highway. Have not yet tried in 4wd.
Rear diff sounds no different than months ago. Have no problem shifting and clutch is not chattering.
Vibration starts at about 35. If I punch it vibration goes away till I let of gas, or upshift and ride steady on gas, then vibration again.
Tires are balanced and running smooth. running about 34lbs all around, and have been. No problem there. The vibration feels like running over highway rumble strips, however at a higher frequency. Steering wheel as well as dash vibrates, but steering wheel and steering is steady with no shimmy at all. Lower or raise air pressure, no change.
I've had bad U-joints in DS before, and this is not the same. Nothing loose underneath and all U-joints feel nice and tight. muffler is nice and tight, as well as tailpipe.
I'm thinking maybe bad engine mounts. They have never been replaced.
Any ideas or feeback quite welcome.

Red Rubi

It seems like you've checked every thing. I still think you have a bad u-joint. If all the needles are only missing in one cup, it will still feel like it's tight when you try to move it. Good luck!

yellowjeeper85

i once had a similar problem in my TJ... turned out to be the DS u-joint... it was tight so i never assumed it to be bad, however, three caps were clean and greased and working fine, one dried up somehow and shook the hell out of the jeep... started mild then after a week or two got worse fast. I would disconnect the DS from the diffs and try to see if the U joints move freely in all directions. Or check your motor mounts. If it turns out to be them, i baught the MOORE Poly motor mounts for my TJ too... they were the raised mounts and helped with driveline angles and even though they were the poly bushings, the difference was negligable from the stock rubber bushings to the poly ones (some people complain they transfew more vibes into the cab than the rubber ones) or if poly doesn't interest you, they make bombproof rubber mounts... more money though. Poly was like 80 bucks. good luck i hope you get it figured out.

xjtrailrider

I've had this issue on a couple of my XJ's after a lift was installed. What I found was the slip yoke is chattering on the T-case output shaft. The slip yoke will actually vibrate on the shaft during quick accel and decell situations.

If you are sure the u-joints are in good condition then try this; pull the drive shaft by removing the 2 u-joint straps at the pinion yoke and pull the slip yoke off of the T-case output shaft. Put some LUCAS RED n TACKY grease on the output shaft splines then reinstall the drive shaft. If the noise goes away then I would suggest that you get a slip yoke eliminator and get away from the stock set-up.

The grease is only a temporary fix and a diagnostic aid, it will start chattering again

Lorrel

As I said, everything I did to the XJ has been done for the last 10 years, however thanks for the input.
For those of you who thought the u-joint was bad. You were right.
Thanks for the inputs from those of you who posted.
Seems I screwed up and originally checked the DS with the XJ in gear. Tonight after work I checked it again, this time putting it in neutral. I had more play then I could believe.
Just got back from a test drive, after replacement, and there are no vibrations what-so-ever. Like night and day. First let me say, doing this in my driveway was not bad at all. Had a u-joint in the tool box I carry in the XJ, along with about 60 lbs of tools and what not. Dropped the rear DS by simply unbolting the four 8mm bolts that hold the rear u-joint to the pinion flange. The double cardon made it pretty easy, as well as the 33's and 6" lift. Was able to crawl right under. I used the rear zerk fitting on the drive shaft as a mark. After unbolting and letting the drive shaft come down in the rear, I sprayed the shit out of the u-joint with bust rust. Went and had a beer. Came back out and using a socket, held the DS and drove the joint cap out with a hammer. It came out pretty easy seeing that once it was out the needle bearings were gone in both of the caps on the DS. That's right they were turned to rusty dust. After getting the joint out, I cleaned everything up, sprayed everything down with Mobil1 synthetic spray and had another beer. Came back out, cleaned everything up, and inserted the new U-joint in the DS, just tapping one cap in a bit to hold the needle bearings in place. Had the 5spd in nuetral so the DS could move around. Next pushed the other cap on and holding the DS and socket, seated it. Installed the snap ring, then tapped the other side a bit. Bolted the other side of the u-joint to the pinion flange, just snug enough to hold it in place, then just drove the other cap home and installed the snap ring. Had to back up the XJ a bit so I could get a good angle to seat the other cap. Once that was done I tightened the bolts and that was that. Used my grease gun with Mobil1 synthetic grease to fill the caps untill the grease started coming out. Never had to take the X-fer case of the DS side out. Checked both the pinoin seal and the x-fer case seal. I was lucky, as bad as the u-joint was, No leaks.
Drove about 10 miles for a test, and was very happy with the results. Crawled back under to clean the excess grease up. Now this new u-joint should be good for another bunch of years. The whole removal/install took me about an hour and a half, and that's including the 2 beers.
A happy XJ'r here. Hope the wifes 07JK lasts like the XJ.