Play in rear transfer case output shaft causing driveline vibrations?

[ktmall07]

Hi all,

 

I recently completed an 8.8 swap, and installed a rusty's 3" lift front and rear at the same time, and have since had some driveline vibrations at high speeds (> 55 mph). 

 

I've narrowed the vibrations down to the rear driveshaft, and checked u-joints first (both were replaced on installing the new axle, and seem fine, they're a few months old). The new 8.8 flange adapter is in good shape as well, it was brand new when purchased, and nothing on that end is loose/worn. 

 

I did not install a slip yoke eliminator, because my lift height is not extreme, and pinion/t-case angles are close enough to have almost no slow-speed angle-related vibrations. When inspecting the slip yoke, it seems that pushing up on the driveshaft right below the u-joint causes the transfer case output shaft to move just a hair (< 1/8", just enough to be noticeable). The movement is only up/down, not side-to-side, no matter the position of the u-joint/drive shaft. Maybe the lift itself has put just enough pressure on the bottom of the output shaft to bend something?

 

My question is: Is any amount of lateral movement in the output shaft normal? I've read that excessive movement could mean a worn tailhousing bushing/seal? There's no real leak from the tailhousing (or the transfer case generally), so not sure if either of those things being worn would be noticeable enough to diagnose without pulling it apart. I also haven't taken off the slip yoke since I reinstalled it. I can't tell if the movement is from the output shaft itself or the slip yoke, but it seems like the movement is from the output shaft (when pulling in different directions, I can't move the slip yoke at all, there's no play in it on the end of the output shaft I don't think). If I have to take everything apart to check anyways, Is an SYE necessary/worth it? I thought I was good without one since the lift was not extreme, but maybe better safe than sorry? Any input would be appreciated.

 

Thanks!