the 1" lift shackles will change the castor angle and you will find your Jeep now will wander pretty badly as a result. You will need to shim the front axle to correct that. A 3 1/2" lift, from my experience, will require a SYE and CV driveline to get rid of the vibes. The slip yoke eliminator shortens the transfer case output which allows you to put on a a CV driveline which are longer than stock and to qoute from Tom Wood's website:
"The real benefit to a C. V. (double cardan) drive shaft is smoother operation at higher operating angles and longer life. The C.V. assembly works by intersecting the joint angles at the center pivot point and delivering a smooth rotational power flow or surface velocity through the drive line. Therefore, with this type of driveline it is important to roll the differential upward so that you have minimal joint operating angle at the differential end. As any substantial joint angle would cause the pinion to try to speed up & slow down two times per revolution. Causing what is known as a torsional vibration. (Torsional vibrations will also be created in a 2 joint driveline that has unequal angles at each of the "U" joints). Rolling the differential upward will lessen the total operating angle at each end of the driveshaft. Now at the transfer case end of the driveshaft you have two joints equally dividing the total angle . This will double the life of the joints at this end, additionally you will be back up to full rated life for the joint at the differential end. I also believe a C.V. is stronger than a conventional driveline when turning through the same angle. This would be the result of transmitting the torque in a plane more perpendicular to centerline of the driveshaft."
Also if you have 3.5" of lift you will want to install a drop pitman to get the steering geometry corrected or you will have what is known as a death wobble.
I had to do all the above on my rig after a 2.5" OME lift which, like yours netted 3.5"
Last edited by Talos; 08-21-2006 at 12:02 PM..