sometimes slight and sometimes rough vibration between 44-52mph

I didn't want to steal the other new guys post.

So here goes..Last week I changed out the Sprag for an Air-Shift. Now between 35-48 I also feel the uuuummmmmmm..uuuuummmmmm in the seat. I did a test with the e-brake and can feel a vibration at all speeds that corresponds. The Sprag did not have this vibration at all. I did notice a noise and an "easy" spot in the u-joint between the transfer and the rear axle. I suspect that is the problem. I will replace it.
Now the question. Has anyone else had this and did it fix yours?
Curtis

Please clarify....
What is your "e-brake test"?
& what do you mean by an "easy spot" in the u-joint? Is it a loose joint?

Check the parking brake drum, for runout(warped).

I slightly engaged the e-brake during operation. I could feel the vibration much more in the e-brake.
The u-joint would move much easier in one direction than another and very much easier in one spot.

It sounds like your new t-case has a warped parking brake drum. If the Parking brake is left on accidentally, it gets hot! This is a common cause for it to warp and create a vibration at near highway speeds. If you can feel it in the P brake handle, as you apply it while moving, I think you found your issue.

One of mine had a vibration / shudder that would oscilate.
I found bolts loose on the drive shaft between trans & tc.
have not driven it since, but I think that is the cause. (but maybe just the result of the vibration?????????)

Loose driveline/driveshaft bolts do cause a harmonic vibration and are commonly found on the M35a2 trucks(especially the short shaft between the trans and t-case).

Since he said it is a new vibration, after swapping the T-case, I am thinking Parking Brake drum.

Runout on the Air-Shift .015
Runout on the Sprag .0025
Looks like they are going to get switched.
Thanks doghead...
Curtis

I changed out the Brake Drum's and that did not fix the problem with the uuuuummmmmmmmmmm....uuuuummmmmmmm. But now I do not feel it in the e-brake. I can feel it in the High/Low range handle and not in the Transmission shifter. The air-shifter has also dropped into neutral 2 times. I am think that I have internal problems. So I will piddle with it a while and keep Murphy busy so you all can move some things travel or what ever.
Thanks for you advise.
Curtis