My son was called away (Army) on emegency immediately after completing lift of my 99 wrangler 4.0 manual las night. Driving it for the first time this morning I found it has severe vibration at acceleration/decel. No vibe with clutch in or in nuetral at idle. He used a procomp 4 inch lift kit for 33 in 12.50 tires. He says that the geometry should be correct for the lift and lowering of system to match it. He's lifted sbout 30 jeeps, including my previous one, without a problem. Don't see any problem with ujoints, confirmed by local mechanic. Vehicle is 8 years old, but only has 9000 miles on it. Preowned by rich dude pulling it around on a motorhome, so it is is mint condition. The vibration is so hard that I cannot drive it for fear of tearing up transfer case. Seems to be no vibe when in 4wd, or my imagination. Need help and I am a complete novice in this area. Anybody have any ideas? Thanks!!!

If the 4" lift is only thing that was done to it since the last time it ran without vibration, I'd suspect a drivehsaft problem. You say the driveshaft u-joints are OK, so I'll take your word that they aren't worn. I doubt that it's a bent driveshaft, or an out-of-balance driveshaft, since those problems would also cause vibration when coasting.

It ksounds like the lift caused the driveshaft to tilt at a higher angle than the u-joints will allow. It's probably right on the edge of working right, but not quite. When the vehicle is coasting, the u-joint angles are just barely acceptable, thus no vibration. However, when you accelerate, you are inducing some axle-wrap (accentuated by the longer leaf springs). The axle wrap causes the axle pinion to rotate, and the u-joint angle becomes more severe, and vibration occurs.

Some people lower the transfer case to lessen the driveshaft angle when lifting a vehicle. However, I'm against that solution for two reasons: (1) It decreases ground clearance under the t-case, thus partially negating the reason for the lift and larger tires in the first place. (2) If you lower the t-case, it may help the rear driveshaft angle, but it makes the front driveshaft angle worse. Also, it results in your engine and transmission being given a constnt nose-up attitude. It's possible that such constant running could affect oil flow over the life of the vehicle. Not sure about the latter, but it is theoretically a problem.

So I'd recommend what I and others have done -- replace the front u-joint on the rear driveshaft with a CV (double-cardan) joint. That will not be cheap, because it will probably involve shortening the driveshaft a little -- although that may not be necessary due to the lift causing a longer distance between the t-case and the rear axle.

If you do install a CV joint, after it is in, install shims under the rear leaf springs in order to point the pinion directly at the rear of the t-case. With a CV joint, you DO NOT attempt to get both ends of the driveshaft at equal angles, like you do with two regular u-joints on the shaft.

Just my thoughts. Hope this helps.

This is a 99 Wrangler (TJ) we're talking about here. It doesn't have leaf springs, etc., which I suspect has totally confused Mr. TooOld. I will assume that you are recommending a slip-yoke eliminator kit to go along with this CV shaft. That will actually allow the rear shaft to be a bit longer, due to the replacement of the rear output housing during the conversion with a shorter one. TooOld, look up SYE kits, and you will see how this will fix what's ailing your Jeep. Good Luck. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Thanks. I'm trying to learn this stuff. Son is sick over the problem but not much he can do. Live in rural area, so tough to find tech support so will have to do it myself. Again, thanks for the info.