Alright, I crawled under the truck and checked the u-joints, and I'm not even 100% sure what I would be looking for... The rear drive shaft was solid as a rock, I couldn't shake-rattle or roll it at all.

The front drive shaft, well, that one was another story. I could move it no problem, it would turn about a half inch in either direction, I don't know if that's normal or not? I would suspect that since the transfer case is in 2WD, the front shaft isn't locked?

But yeah... I didn't really feel any looseness in any of the u-joints.

 

I'm not a 4WD expert in any way, but I don't believe either driveshaft should move too much whether it's in 4WD or not. Even though the transfer case end is floating, the front diff end is still connected, and if the front wheels are on the ground then it should be solid. If the play isn't obvious on the outside of the shaft you might have to pull the front diff cover to see what's going on.

A question to add on to this for the pro's out there..... when the front or rear driveshafts are pulled, should they be marked so that they're installed in the same location on the yoke to maintain a "balanced" relationship between the two? In other words, if the front shaft is reinstalled 180 degrees rotated from how it came out, would it cause a vibration?

Bob

 

Alright, well, here's what I did today... I took the truck out on the highway, I accelerated to 75MPH, at which point I put the gear selector in Neutral... Then I grabbed the transfer case shift **** and put the transfer case into Neutral as well... And then I coasted.

As soon as I hit 65MPH, the vibration began, getting worse until 55MPH, and then it went away.

In my opinion, this completely rules out driveshaft or u-joint problems, because with the transmission and transfter case both in neutral... nothing would be moving.

The vibration must be coming from elsewhere.

 

I don't think that's a true statement. Even in neutral, 4WD or 2WD, the front and rear driveshafts are still in motion, being driven by their respective differentials.

I'm assuming tires & rims have been ruled out? A shifted belt in a tire will do this as well.

Bob

 

I think you have a bad tire or there out of balance

 

Okay... I guess that makes sense. You're probably right.

And yes, tires & rims have been ruled out, the first thing I did was take them in to get re-balanced. They weren't even out of balance. But I had them re-balanced anyways. The tires are brand new, so I really doubt there's a seperating tire or anything.

 

they do make bad tires from the factory

 

I was a tire tech for 10 years i know a little bit about tires

 

i just went out and checked my truck, the rear driveshaft is the same as yours, solid as rock, doesnt move at all, the front is also the same as yours, has some rotational play in it, id say your probably fine in that respect.

now your test does NOT rule out the driveshafts or anything else down train of the t-case bc the driveshafts ares till turning as stated above, driven by the tires on the ground thru the differentials

 

Well... Maybe it's time for me to take the truck to a shop with a road-force balancing machine or dyno... They can figure out what the **** is causing the vibration.