Drivetrain angles... I know, its different

99 XJ, 2" spacers with shackles in the rear with a bastard pack. 2 1/2 lift total in the rear. Also have transfercase dropped 3/4" 8.25 rear with a np231.

Im getting pretty decent vibration. Not tolerable over 65, at 30 and 55 im getting a vibe that feels like out of balance tires (not out of balance)

Low frequency vibe at 30 and 55 (makes the seats shake, visible if no ones in the passenger seat.) Over 65 feels more like a bad u-joint. Higher frequency with a droning vibe that comes and goes every few seconds.

New u joints in rear driveshaft, have front pulled for testing.

I am really surprised im having this much trouble on 2 - 2 1/2 of lift. If people can run around on four with no sye, I find it hard to believe that its this bad on 2".

So what I'm asking is if im missing something stupid. Also how to measure the pinion angle and all that. Doesnt seem to be a decent flat spot on the diff to work from.

Tons of info on this, probably even a sticky.

You are claiming 2.5" lift with 2" spacers, a bastard pack, AND shackles?
2.5" in the rear can be accomplished with just a AAL, why all the extra stuff?

The FSM suggests using using the yoke ears. I find that a socket that fits inside the ears on the actual u-joint works for a good flat spot.

The idea is equal and opposite. If the DS is points 5 deg down at the front yoke, the DS should point up 5 deg from the back yoke.

Take out the drop, you don't need it, in fact, it may be a contributing factor.

Lube the snot out of the slip yoke. On a 97 and up, that thing can bind and cause issues.

I have 3" on my 98', just front springs and a bastard pack out back. Never had an issue.

Yours is a common problem with the late model t-case.There was a TSB put out with a "mickey mouse" solution.Best solution would be a SYE kit.

The bastard pack was put in and ended up sagging over the course of two years so I added the shackles to compensate.

So as springs sag (mostly S in the front 1/2), they tend to point the nose of the pinion up. To compensate for the sagged springs, you added lift shackles which point the pinion even more up.

Then at some point you lowered the T-Case which dropped the back of the T-Case, and decreased that angle.








OK tear it all out and start over.

Get rid of the T-Case drop. Go BUY some new springs. Put the stock shackles back on. Then see what you have for angles. If you have to adjust the drive line angle, figure out what size shims you need at the rear axle to fix the issue. The shim goes between the spring perch and spring, they come in different sizes.

We can't help you here.... go ask at pirate4x4










just kidding.... alot of people have trouble above 2" in the late models... I see a SYE in your future