I took my xj for its first drive today after the RE 4.5 inch lift. I did not expect and vibes because I installed a sye and front xj drive shaft, but vibrate it did. I assume this has to do with pinion angle? Would the vibes go away if I installed the t case drop included in the lift? Or and rear axle shims the only fix? I would probaly go with shims but for right now I would like it be tolarable to drive. Also, do the shims lift the rear at all? because right now the rear is slightly higher than the front and I dont really want it be get taller.
I did a front 4.5" suspension lift (skyjacker) and an equivalent bastard pack in the rear on my '97 and had vibes over 60mph only.
This XJ was equipped with the weak D35 rear axle and 231TC, but it was like new as the previous owner must have wore it out. . . So, I got a longer shaft from an XJ with a different set-up and coupled with some very minor (sorry forget the deg. mesurement, but thought it was ~5?) axle shims was able to get a PERFECT ride out of it. You could probably source the main shaft from something (anything) that has the same size holes for the u-joints as your yokes.
This XJ is kinda a DD, but where I live that means light trails everyday and medium on weekends, etc. My other XJ had to undergo the HnT SYE as its a 242 and I sourced a flanged connection shaft from a 4x4 shop here that was with in a 1/2" of being perfect.
So... the point is I would look for a longer shaft in your lift height and if you can gain 1-1/2"-2" you will do great. Then the shims at your leisure will seal the deal .. .
I know folks will say go with an SYE right away, but this is my opinion. These Jeeps are so forgiving. I love them.
If you have an SYE, you do not need a T-Case drop, and you will need shims for the rear axle. The are less than 1/4 inch thick, so no noticeable lift. One at a time, pull the front/rear driveshaft and go for a test drive so you can determine if either driveshaft itself is the source of the vibes. Front pinion angle can also cause vibes.
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I just went out and checked the drive shafts again, and I noticed some movement in the DC joint on the rear junkyard sorced shaft. The movement feels pretty minor, and I cant pin point where it is coming from, but both u joints at that end dont seem to be it and I dont think it is slop in the t-case either (although there is a little there). Looks like im going to have to install some shims and see where am at from there. I still need to measure the angles to determine what shims I need. When I install them, will I need linger center pins? and should I but rubicon express shims so they are the same brand as the leafs?
I just reamed out the shim to go over the pin. The shim is then sandwiched between leaf pack and perch. I've done this twice and never had an issue. Guessed on the angle both times. Not proper, but I'm a carpenter, so if it resembles a certain pitch I translate and source a set from the local used jeep store.
I went out and bought a magnetic protractor to measure my angles. The drive shaft is at about 22-23 degrees and the yoke is at about 13 degrees. The jeep is on a slight hill so thats why the numbers might seem high. So I should get a 8 degree shim? The protractor has a tolerance of 1-2 degrees. Why does it see like the difference is so large? Or is that normal for a RE 4.5 inch lift?
After searching quite a bit I found the RE springs use a 3/8 pin. I was thinking, the weight of the jeep for about a week. So would it settle more that it is? If it does that might make the 8 degree shims too much. Would be better to get 6 degree shims and be under or 8 degree and possably be too much. Also would measuring on a hill mess up the measurments?
I just remeasured on level ground and got the yoke to be at 9 degrees and driveshaft at 19 degrees. This would mean I would need a 8 degree shim? Why does it seem higher than what other people with similar lifts are getting? How much will the rear settle because right now it is about 3/4 inches taller than the front.