Another 98XJ driveshaft vibration question

Anyone have this problem that I found in an old post (Even the Hack-n-tap kit didnt work for me and had to Re-invest in a HD Sye!)? The reason I ask is that I'm chasing a vib., I did the hack-n-tap with double cardan joint driveshaft. Axle pinion is inline with shaft at 4* shims and pointing at just below tcase shaft. Even tried 6*, still vibrates at 60+. I Had Englewood Driveshaft check out my new HIGHANGLE driveshaft because it DIDN'T have a weight on it! It WAS bent .020 and of course out of balance. After all that I still have vibes. I searched and found the above h/t issue???? Just FYI, before lift no vibs, after lift with only a tcase drop vibs only between 20-40. After h/t & DS vibs only over 45++++...With re-balanced ds over 60++ And when it starts its like flipping a switch on (stops when I let off or go below 60).

Try dropping the rear driveshaft completely. Put it in 4hi and see if you still get the same vibes.

Another way is to put the rear axle on jack stands and run it up to that speed in 2wd with out the tires on the ground. You can then normally see/hear where the problem is if you crawl under the vehicle while someone else controls the throttle. Just a note: Pick all the rocks out of the tires before you do this. They have a nasty habit of exiting at the wrong time. Also get the tires at least a couple inches off the ground. As they speed up they get taller and can start to touch if the clearance isn't sufficient.

I have a funny suspicion that due to the accelleration component, you may have a pinion bearing that is getting loose. I have even seen a wheel bearing cause something similar. Is it more of a vib through the body or a noise?

Just for kicks, take out the front D/S.
I could have sworn my vibe was coming from the rear, but the unibody plays tricks on you.
I recently found a clunk that I had been chasing for months.
After replacing the steering, LCA bushings, track bar(50% of problem), and found that when I did the uppers, I didn't tighten the bolt enough due to the engine proximity.
To paraphrase, try taking out the front D/S.

What wheels are you using? I had a set of American Eagle's steel wagon wheels that would vibrate every time.. it was like something was out of balance but the tire-guys did it 2x and the same thing happened. Switched to a milled alloy and its gone...

but, on the stop and go it still clinks and clanks.. for a 99 that just won't do.

I'm pretty sure that is from a rear pinion gear loosening. I think that with the lift you need to take out a spacer or two from the pinion... I'm going to try it and see if the play is coming from the gear.

PINION GEAR!!!!!

check it

Thanks for the replys but found the problem!!!!!!! 6* shims and a poor hack-n-tap job (by me). Before when figuring the pinion angle I was eye balling the pinion with a straight edge off of rearend casting lines which looked like they were true with the rearend and it looked like it could go a little more since it was vibrating with 4*. This time I used a square and straight edge off of the pinion flange and found the pinion pointing high of center to the tcase output shaft. So I pulled the 6* out, put the 4* shims back in and that put it a little low of center. While I had the driveshaft off again I put a dial indicator on the hack-n-tap and found it out of square!!! My saw cut was not perfectly square, so when I tighten down the h/t it torqued it out of square. I removed it, squared it off, put it all back together, test drove and ALL VIBS ARE GONE. Between the new drive shaft that was 15 thou. out of true and 12 grams out of balance, h/t that was out of square, and the wrong shims no wonder it vibrated. TAKE YOUR TIME AND MEASURE, saves 3 days of wrenching.

Whats wierd is that I've had a 3.5 inch lift with 31s for almost 4 years, and all I have is the T-case drop and I have never had any driveline vibration? Although I am in the process of adding 2 more inches of lift and 33s, so I'm sure she'll be shakin soon.

Initially I did the tcase drop with stock drive shaft and only had slight vibs between 20-40mph but being picky I wouldn't leave it alone. Its when I went to the sye that all hell broke loose. At least i'm vibe free now!

Good deal, glad you got it fixed.