Driveline vibes. Done everything with no avail.

99XJ 8.25 np231 auto

This all started when i built a big bastard pack. Ended up with about 3.5" in the rear. Installed a T-case drop. Had vibes from 60mph up.

I later pulled a couple leafs from the pack and put on a set of shackles. I ended up with about 1.75" over stock. I pulled the tcase drop then. I had vibes from 65mph on. Getting bad enough at 70 that you can hear it not only feel it.

I now have a tapered 5/8" block and my pinion angle and tcase output angle are within a degree. Probably half a degree down at the pinion.

I still have the same exact vibes that I did without the tapered blocks. I would think it would at least get worse or better with the change. Any ideas what to do next? I really dont want to put an SYE in for a 2" lift. Vibes arent liveable at highway speeds so I dont think I have the normal vibes.

There are many things to check, but the first thing I would do is to have your rear driveshaft re-balanced and possibly rebuilt. The u-joints are not operating in the same range they had been before, so they may be out of whack. Get your front driveshaft checked as well if that doesn't do it as the front shaft is spinning all the time.

I just put on my new lift and tires. Ends up my drive shafts needed to be rebuilt because of a bad pinion angle. I have had a SYE with vibes for a long time trying to fix it now. Now my tcase is getting rebuilt bad bearings pump chain and other stuff lots of fun 600 bucks later my fault for not knowing?!? Ohh well... All in all I had vibes when I had the slip yolk, still had them after the sye and now we will see everything has been replaced or rebuilt. Just keep checking everything till you find what is wrong. I would definitely check those u joints though once you change the angle. for sure if you had vibes before the lift, your joints can go bad. Also have you had your drive shaft lengthened after the lift?

I'd try pulling your front shaft and take it for a drive.

If still nothing then take out the rear and drive with the front

pull the rear driveshaft and check for slack in the centering yoke on the double cardan. if this becomes worn out it will vibrate like that.

Check your tire balance & / Or rotate front to back, too.
Happens all the time & to the best of us : we change one thing, notice another, and mistakenly think they *must* be connected.
Of course, you might just have worn / sloppy u-joints, too.

Jeepwire.Com Presents: Setting Your Pinion AngleThis shows you in detail what to so with or without a TC drop..real straight forward, and you will need a angle finder..