TJ's are coil all the way.
Several ways to attack your problem, but it helps to plan your mods to fit with future mods so that you don't have to buy the same thing over and over again.
1) Adjustable control arms.
A good investment. One that will work with lots of different setups and can be adjusted when new mods make angle changes necessary. You can get by with adjustable arms on bottom only, but if you put them on top and bottom, it gives you more control on positioning the axle from front to rear as well as rotating it. When you shorten lower control arms, that causes the pinion to roll upward, but it also shortens the wheel base a bit. This becomes a problem with larger tires, 35's, because the tire will hit the front of the fender well at the bottom corner (rear axle). By lengthening the arms you can move the axle rearward and clear the corner and still keep the rotation where it is supposed to be.
2) Off set bolt (cam action) in frame end of the (lower, I think) control arm.
Jeep sells a bolt that has a cam action so that as it is rotated it moves the front of the control arm to the front or rear thus rotating the axle a bit. This is a cheap fix as opposed to the adjustable control arms, but it has a very limited range. Am not sure whether it is the upper or lower arm that takes this bolt. Lower, I think, but might even be able to put it in both. You need to check this out if it is of interest.
3) Drive shaft.
A CV drive shaft is another good investment, but there are variables here too. Best option is to change the tail shaft of the transfer case AND the drive shaft at the same time. This is another mod that works with other modifications without having to be redone, unless you change rear axles, that is. Changing the tail shaft accomplishes other things too. It is shorter so that you can install a longer drive shaft and thus decrease the drive shaft angle, and it solves the problem of losing oil from the transfer case if you have to remove the rear drive shaft.
4) Extended height motor mounts
You can install a 1" taller motor mount - available from Currie - to raise the motor. This changes the angle of the motor, transmission, transfer case to the rear axle. It is a very slight angle change, but where just a little bit of angle change is needed, it works well. If you have a body lift, the motor mount lift will also help to get your engine fan and radiator back in line so that the fan does not hit the bottom of the fan shroud.
All these things are fixes for the drive shaft angle problems that develop when you install a lift. Also keep in mind that the angle setup is different for a regular u-joint (stock) drive shaft and a CV drive shaft. U-joint splits the angle of the drive shaft between the u-joints. CV joints take all the angle at the CV end and a maximum of 4 degrees at the u-joint end (pinion end). Lowering the transfer case to take some of the angle out of the rear drive shaft is a commonly done mod, but is probably the least desirable answer to the vibration problem. Why do a lift, then do a lowering job right in the middle of the vehicle where it is the MOST likely to get hung up on high center?
Lots of things to consider. Hope this helps.
Doug '97 TJ
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