this wednesday im taking the drive shafts out and checking the ubolts on the rear axels. I have now put my stock rims back on running 285 BF all terrrains and still having the same problem. hopefully its the shafts

 

You could also remove the front drive shaft meantime. You'll at least know if that is the cause or part of it anyway.

 

The only thing I didn't hear you mention is the idler arm. I've had a bad one (worn bushing where the arm pivots, not at the ball joint) cause vibrations a-plenty.

I'm not thinking driveshafts because you said the problem started when you first switched to the big tires.

You've probably already done this about ten times, but make sure there's absolutely no play anywhere in the steering linkage when someone turns the steering wheel back and forth vigorously, and you watch like a hawk. Rule out excess play inside the steering box as well.

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Edit: Just re-read the thread, and since you're not feeling any vibration at the steering wheel, please ignore most of the above.

If I read correctly, you've observed some play in one of the rear driveshaft u-joints, and haven't replaced it yet. If that's the case, I now change my bet to that. Still doesn't explain why it started with the tire swap, but oh well ...

Lastly; pinion nut nice and snug? Any play at the pinion bearing? Could be the diff. I once had a pinion nut come loose, and the pinion drop down into the diff. Right after it happened, I thought back and realized that she'd given me a bit of warning that she wasn't happy; lots of rumbling and vibration.

 

In the service manual there is a test procedure for an unbalanced driveshaft. In the 96 book section 3 page 4.

 

Good thing, because there is no idler arm on a 4x4.

 

"Good thing, because there is no idler arm on a 4x4.".

Now that really hurts; just no way around it. I got nuthin', so I'm off to get blind drunk. See you all tomorrow, around noon.

 

Good call, I'm half way there myself.

 

That's an every day occurrence fer me.......

Any update on this?

 

so i took the drive shafts out today and they were balanced, installed new u joints and when I went to put them back in found that the new TC out put seal was the wrong one. So picking up a new seal from dodge friday and putting everything back in.

I also installed a new moog trac bar, although the one in there seamed to be fine there was a little bit of play. after the install had an alignment done and still the vibration/shaking was happening.

we will see what happens friday when the shafts go back in. Thanks for all the ideas your info helps out a boat load

 

Mine shakes exactly like yours at precisely 75 mph. So figure it out already! Lol I heard if the wheel bearings are messed up they can cause this too, but that could just have been a mechanic who wanted my money