Driveline Vibration and How To Cure It on Lifted Jeeps

This is a copy of an e-mail that I just sent to a good customer of ours, that I thought might benefit someone else, looking to eliminate driveline vibes from their lifted Jeep. Feel free to comment below for clarification, and I’ll answer your questions/comments as quickly as I can.

Here’s his original e-mails, compiled, which may sound similar to the problem you’re currently having too:

-I’ve had a Clayton kit and about 7″s of lift on my WJ for quite a few years and finally decided that I’ve had enough with the vibration from what I believe was the front drive shaft. The rear was replaced prior with a Tom Woods and both were looked at by ADS in Mesa yesterday. They informed me that I’m basically screwed with the front angle off the t-case and the vibration will never go away. What have you done in the past or seen to help remedy this issue? I have a factory double-cardan on the front. ADS said it’s short, but not causing the issue in their opinion, simply the angle off the yoke. I’ve got to start using this as my daily driver again and want to make it sound. My current front drive shaft is a stock double-cardan style with fixed yokes at the t-case and axle, then the shaft is a splined slip to accommodate movement.

Please show me the light. Thanks in advance.

And, here’s my response:
Ok, so the FIRST thing, IMHO, that absolutely HAS to be done, is remove the front shaft, and drive around for a few days, during your normal schedule, and see if indeed ADS is correct, and the vibes are eliminated completely, or not. (I’m guessing not!) You could have TWO different shaft vibe problems, so removing the front shaft, and dialing in the rear to the best you can get FIRST, is the way to cure that “knowledge deficiency”. If you still have a stock set of tires, consider swaping them on, to reduce mud-terrain noise/vibes from the equation.

Once the rear gets dialed in as good as it can possibly be, consider removing it, replacing the front, and driving around testing it in ONLY Front Wheel Drive. This *SHOULDN’T* have any short-term ill-effects on your NP247 case…it *SHOULD* just lock into it’s 50/50 mode, and that’s that. I’d suggest not doing any “long-term” testing on my theory/belief, though, unless you already have an NP242 or 231 ready to bolt in, and just want to find out if I was right, for sure, lol, but short-term (a day or two), it should be fine.

And, that’s the process to eliminate the vibes, my friend…like it or not, lol. It ain’t easy, but after fine-tuning my WJ, I’m able to do 80mph with VERY little driveline vibe (tire vibe is another thing, completely, lol). However, I’m also running a high pinion rear axle, and the front pinion yoke has been “re-indexed” upwards, via separating the tubes from the diff, twisting it upwards, and re-welding it, to the tune of around $1k. At the time, it was the quickest solution, but longer-term thinking would have netted me a replacement front diff with a high-pinion, of the D44 variety, instead.

Ultimately, you have Physics working against you, pure and simple. Irrespective of the driveline setup, having the pinion yokes of the t-case and the axle being separated vertically by several/many inches, you’re inherently going to have vibrations…and the more separation, the more vibration. Period. Less lift = less inherent vibes…end of story. High pinion axles are one Physics-related vibration solution, and lowering the t-case is the other one. Driveshaft configuration merely makes the best of the problem you already have…vertical separation of yokes.

Do let me know what you end up finding out after removing the front shaft. I’d be pretty surprised if the front shaft is your MAIN source of vibes, frankly, based on my experience.

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