Driveline vibes

My friends jeep (no really ) had some driveline vibes after we installed a 2" lift. We dropped the transfercase about 3/4" with some hard rubber until we could get some shims. Seemed to get rid of most of the vibes you could still feel it accelerating up hill. He replaced the u-joints cause they where bad but it didn't fix the vibes.

We measured (with the transfercase drop out) and ordered shims to bring the pinion about 1degree below parallel (mine seems to work good at that angle) and installed the shims last night.

Vibes are worse than before. We put the transfercase drop back in with the shims and the vibes almost go away but still under load going up hills you can feel them a little.

So it seems changing the pinion angle doesn't affect much but dropping the transfer case does? Problem with the slip yoke maybe? We're stumped if anyone has got any ideas.

EDIT:
Also the pinion was pointed up 2.5 degrees past parallel before we shimmed it. We thought that was causing the vibes.

with a slip yoke in the tranfercase and no SYE, you want the transferace output shaft/slipyoke and the axle pinion to be parallel with each other.


did you put the shims in with the thick part facing the back?

what type of 2" lift? shackle or add a leaf?

Really? Mine seems to like to have the pinion pointed 1 degree down from parallel. I always assumed it was because under acceleration the pinion tried to point up.

The shims are in with the thick part facing forward and the lift is an extra s10 spring.

Before the axle shims (and no transfercase drop) the pinion was pointed 2.5 degrees up from parallel and after the shims it's pointed 1 degree down.

The thing I find most interesting is that it seems to ride the same with the shims and the transfercase drop as it does with just the transfercase drop.

With or without the shims there are almost no vibes with the drop but a lot without it

Just a follow up.

Turns out the output shaft was bent. Don't know how but it was obvious watching it spin with the jeep in gear. The transfer case drop helped because it pushed the slip yoke deeper which making the distance from the case to the u-joint shorter made the distance it was off center less.