Drive line vibrations from hell

Ok guys, Ive done everything I can think of. Started as a 99 4x4. Added 3.5 RE ultra ride. Then had to fix the death wobble with a new track bar. After that were awful, violent car bouncing vibrations. Went with 4 degree shims. Much better but still had vibrations from about 30+ mph. After that went with a H&T SYE and a front DS. This is still with the 4 degrees. Much better but still have vibrations at 30+. Measured the drive line at about 9 degrees of difference so I went with 8 degree shims this time. This moved the vibrations to about 56+ mph. With the worst being from 56-65 mph. Its still very annoying and not something I can just deal with. I am a lighting designer and carry 1-2k pounds of gear to shows. With the jeep loaded the vibrations sounds like the car is going to fall apart. Like a plane taking off after 55 mph.

We have 3 other lifted (no shims, no SYE, no vibrations) and 3 more non lifted XJs in the family and I work on all of them. Mine is the only one with this problem. Everyone says X is how to fix it and nothing solves the problem. Im about to just trash it and get a gas getter. Any Ideas out there. Im thinking a real SYE but could this be an axle or tranny problem. Anyone have anything smiler.

Have you had the tires balanced recently? Usually a driveshaft doesn't have enough force to do much other than vibrate and make noise. If you are bouncing, and given the specific speed I would suspect the tires, I had the same problem when a belt was seperating on one of my tires. A bent rim will also do the same thing. Try rotating the tires and see if the vibes move.
Another thing is check the ujoints, they don't last long at improper angles, especially as extreme as you mention.

It only bounced right after it was lifted. Now its just a constant massage and makes noise at 56+. I had the drive shafts themselves rebuilt between every step even with the shop managers assuring me the joints were still good. I keep blowing their mind when I tell them to rebuild them again. I haven't checked the tires/rims after I got new BFG ATs last fall. They might have 5k miles on them. But heck, ill try it.

I know that story, rebuilt my shaft twice with a new centering ball last time around. Finally replaced the shaft as the centering stud in the DC was suspect, solved my issues right there. My vibes were more resonant, started on acceleration and would disappear on coast, back when I hit the gas.
Still have a vibe in the front but have higher issues to deal with there first.
Try the tires, usually a driveline vibe will be there at all ranges in some degree, tires tend to have speed related vibes.
How are the trans and motor mounts?

Sounds like what I went through......http://naxja.org/forum/showthread.php?t=1090657

Hans

I don't know the history of your XJ, but is it possible one of the axles isn't perpendicular to the line of travel? Check it for square and you should have that answer pretty quickly. Good luck.

Did you measure the angles after you put in the 8 degree shims? 8 degrees sounds like a ton.

Can you for sure verify it is front or rear? Only reason I ask is I had my steering stabilizer go out and that made me realize it was masking a VERY bad front unit bearing. Gave me pretty violent steering vibration which didn't feel like much when the stabilizer was working properly.

If you know its the rear end id have to agree with checking the tires out, and I also agree with wierdo, 8* sounds like quite a bit on 3.5"... the pics don't work and I'm assuming its of the driveline and pinion angles, host them through photobucket and repost.

Try and remove the front driveshaft, Don't the 99's have a low pinion front axle? I may be wrong, someone will verify.

How are the angles for the front? I noticed you only posted about the rear, nothing about fixing the front.

Once you get up to speed, does the noise stop or diminish if you let off the gas?

Also, I see no mention of an alignment so I assume this was done.

Also, does the u-joint in your rear driveshaft fit tightly in the yoke on the diff? After prolonged vibrations the yoke will "stretch" and the u-joint will no longer sit firmly in the space and will thus no longer be centered. This leads to a constant, droning vibration at speed.