I recently installed a Rough Country 4.5 X-Series kit. It came with 3 degree shims already installed on the spring packs. It also came with a transfer case lowering kit.

After installing it and driving it for a couple weeks, I noticed a vibration around 45. It seems most noticeable if I am coasting down hill, and just barely press the gas. It's like the coast side of the ring and pinion make the vibration go away, and pressing the gas "floats" the pinion in between the drive and coast sides of the gears.

It also vibrates pretty good under heavy acceleration, between 25-50.

I'm planning on taking this on a 900 mile round trip. Anything I am at risk of damaging?

I know I need an SYE, that's coming soon. Before I go, I'm changing to oil, t-case fluid, front and rear diffs, and new rear u-joint.

 

While the problem needs to be addressed I wouldn't worry about any major failures unless you already have parts in bad shape. I have over 50k with no SYE and 5" of lift. Saying that with shackle relocators, extended shackles and 4* shims my angles dont give the coast vibes you describe. Ive had them before I got it setup the way it is now and drove thousands of miles with them. Not ideal and yes you are stressing your ujoints but IMO if you cant fix before the trip and can tolerate the annoyance it will survive.

 

I have zero vibrations at highway speeds, which is 99% of this trip. Hoping all goes well.

 

I'd bring a spare u joint.

 

The sooner the SYE goes in the better so you can remove the TC drop kit and get rid of that stress. 3" of lift is pretty much max for a TC drop kit over that requires an SYE because of the problems in the driveline it cause's. The drop kit also is very hard on your engine and trans mounts.


Install the SYE/driveshaft then see if you still have any issues that need to be dealt with then. I have shims in my XJ with an SYE can't remember what degree they are.