So with no CDL, I'm wondering would this help me seperate front to rear, AND possibly left to right.

If I jack up one tire,chock the **** out of the wheels and basically make it so the truck can't move or fall off the jack, accelerate that one wheel and see if vibration is there. Also, parking brake does it lock up the front driveshaft too or just the rear with t case open.

EDIT WTF AM I THINKING MY TRACTION CONTROL WOULD ACTIVATE!!

 

First you have a CDL if needed. I would first look at your tire tear and have the balance checked. Make sure your u-joints are greased, check your roto flex, if you have one is not cracking between the bolts and make sure your wheel bearings are tight.

 

aside from insanely dangerous, by lifting a wheel off the ground you are changing the load. When you change the load you will alter any vibration. Soo even if this would work Which I doubt it would, the results would be null and void. What is your vibration. Maybe someone on here has had the same or similar enough to be able to help you. kinda hard to without knowing what the vibration is.

 

It's a vibration, that is through all speeds but bad through 25-40mph and starts getting bad again around 70. I changed the front prop shaft, and it seems to have done nothing but change the frequency and speeds at which the vibration is worse. You would think in that case it's driveshaft related specifically front, but I'm just not thinking that's it. Shop put it on a lift and spun it and said everything seemed fine up to 70. They said you could see the obvious vibration in the wheels, (though they said they were balanced) but the driveshafts looked fine absolutely no wobble. However they were guessing possibly something in the transmission or a bearing in the transfercase... Makes no sense to me.

 

What drive shaft model did you install?

 

Ask the shop if they will put it back on the lift, remove the wheels and then run it back upto 70 and see if he vibration is still there.

To rule out the driveshaft...I have heard but have yet to confirm that a Dodge Durango front driveshaft fits the DII as well, maybe you can pick one up from a junk yard for cheap enough to try?
I'm just spit balling here so realize that.

My money is still on the output shaft bearing on the t-case.

 

Oooo...oooo..oooo...dont drive 70!! Problem solved, next question please.

 

Well this is driveshaft #2 I'd really like to think that's not it...

Now if the output shaft bearing is bad I can see how the old heavier driveshaft could vibrate differently from the new one..

I think I might give this a shot, sucks it would be soo much easier if it had a CDL.

 

Just realized my traction control would active and send me flying.. Is there a fuse I could pull or we'll if not.. There's no way I'm doing it

 

Sweet Baby Jesus, that sounds like a Darwin award waiting to happen.

You might not like Disco Mike's answer, but he is right. You need to go about your diagnostic logically and carefully.

Start at the Engine and work your way "out". You say it's at speed, so it has to be the tranny or back. If it vibrates at 25-40 mph have you tried a lower/higher gear to see if it goes away? 25mph you can drive in low range, did you try driving it up to 25-30mph with low range engaged? Did the vibration go away?

You have a new front propshaft, which if I remember correctly from you previous posts is professionally rebuilt. It's probably safe to say it's ok. What about the rear propshaft though? Have you greased it recently? What about the rotoflex joint? Does it look jacked up? They are made of rubber, they dry out and cause all sorts of weird vibrations.

Assuming propshafts check out, the last on the list is to look at the axles. For that though I would recommend working from the tire in. Are the tires new? Not bald? Recently rotated and balanced? Lugnuts look ok? How do the rotors and brakes look? Do you have play in the wheel bearings? With the tire off the ground try to shake it back and forth hard as you can, any play = bad bearings = bad vibrations.

Throwing random parts out there and guessing what the problem is gets costly fast.