Rubicon express 2" lift w/ mono shocks

Any lift can create problems. Since these vehicles are not made to the exact same dimensions, in other words there is some allowable manufacturing tolerance, each one will respond differently to upgrades and changes in geometry. Washers under the skid plate sound like an attempt to straighten out the drive shaft, similar to a transfer case drop kit. This lessens the angle on the front universal joint. It should not be done unless an equal and opposite change is made to the rear universal joint. The transfer case output shaft and the rear axle pinion should be parallel for trouble-free operation.

Another thing that people avoid thinking about is that a transfer case drop changes the angle on the front drive shaft. This shaft is longer and closer to parallel so that it doesn't usually cause problems, but theoretically I suppose it could.

From an engineering standpoint, a slip yoke eliminator kit is a sounder option, as it makes the drive shaft longer and thus less susceptible to this sort of problem. SYEs are expensive, but if it cures your vibration problem it is cheaper than dropping drive shafts on the road, towing bills, rebuilding transfer cases and all the bother that you could have if you don't do something soon.

Cheers,

Earle

Don: When you lift without changing the control arms the pinion rolls up. The washers lower the transfer case to point it down and restore the equal angles for the rear axle. I have a 2.25" BB in my '06 Rubicon LJ with no vibration issues. There is a very slight tendency to crab since the front track bar is mounted to the right side of the axle and it is opposite in the back. The longer drive shaft goes a long way in elimination those issues for mild lifts. Rather than lowering the skid, common practice is to do a 1" body lift and a 1" motor mount lift. Ultimatly the correct solution is all of the above plus adjustable control arms and track bar to preserve the pinion angle, but general wisdom is that this is not needed until 3"+.

-- jeff '91 YJ, '00 XJ, '06 RLJ

Your axle U-joints need to be parallel on either end when they spin to avoid jams. When they get too far out of sync with each other, vibrations start up.

The need to be like this: |----------| or /--------/

If you just change the rear with a lift, you can get this: |---------/ which will vibrate (start jamming) once it hits a certain angle.

A CV or constant velocity joint is one fix.

One other fix involves changing the front or rear angles.

When you lower the skid plate, you are lowering the transmission mount which changes the angle of the tail of the transfer case. Raising up the engine mounts do the same, but that also involves a body lift.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > What are the chances of vibration problems with the 2" lift on a 05 Rubicon

You are correct my install turned out GREAT no vibration and better ride with the mono shocks!!!! I think this was the perfect lift for our daily driver. Thanks for all Help.