Steven Little

Straightsixjeep did you every figure out what was causing your vibrations? I have the exact same issue...

jordan96xj

The first candidate for rear drive-line vibrations after leaf spring replacement is the u-joints. If they are old, then no troubleshooting is necessary, simply replace them. They will continue to vibe for a few hundred miles, but tend to get smoother as they settle into the angle.

The next candidate is the ride height itself, especially if going to the Dorman or Crown replacement springs that give about 1" over the original stock spring. This places the rear drive-line near the upper limit of its specified angles. This will particularly bad when the springs are first installed, but will diminish considerably after about 10k miles/1 year of road use. You will loose between .5 and 1 inch over that time. You can help smooth things during this time by keeping a full tank of gas, and carrying some heavier cargo.

A slip-yoke-eliminator or transfer case drop kit is not needed for stock replacement or Dorman or Crown replacement springs. New u-joints and some miles and some time are the real cure.

The vibe will be most noticed between 45-55mph and will be more pronounced on long inclines because it is not just engine rpm, but the amount of torque load at the rear that is going to bring on the vibe. Conversely, it will seem to diminish when on long declines.

Jettn Jim

Great response Jordan... And pretty much spot on. Next after new U-Joints and while replacing them, would be to check the Output shaft angle in relation to the pinion angle and shim it slightly if necessary.