HI ALL ! New to the forum and new to the Super Duty. Ive owned GM all my 27 years driving... I don't know much yet about typical issues and dealing with them on Super Dutys but will learn. So I'm looking to get a plausible answer to my issue. Truck is a 6.2l Regular cab with manual lockouts. Truck feels like I'm driving on a washboard above 10mph in 4WD. I have tryd just lockouts, just transfer case locked in and both locked in and I get the same effect, obviously the front drive train is spinning regardless which 3 I try. So I assumed I had a bad wheel / hub universal and changed them both out with new. unfortunately problem did not go away. I was told be an acquaintance that they remember something about front drive shaft issues not to long ago. I don't have any other info on this yet. I can only assume I may have a universal in the shaft that could be causing this. Other thought is maybe a bad bearing in the front pumpkin? I'm lost and hoping for some help and guidance. winter here in NY has been typical and March is coming. Id like to have this resolved before the March Lion comes for his annual visit. If there is a post on this issue, please assist me on what that title or link is. Thanks All.......

 

sounds like a bad u-joint in the front shaft or a bad centering ball in the double cardan joint on the end that bolts to the t-case. I would remove the front shaft, lock the hubs and put it in 4X4 and drive it to see if the problem is gone. I just rebuilt the front shaft on my '03 , it was starting to groan and also vibrate slightly.