Bad Vibration at 30mph!

I’ve got a real bad vibration between 25-35mph. It goes away completely once I hit 40, and feels smooth as ever. I just replaced carrier bearing and u joints on the shaft, so it can’t be that. Have recently done CV Axles, LBJ, UBJ, rotors and pads, steering rack and tie rods, as well as changed oil on both difs, transfer case, and transmission. (5spd). Could it be tires? Just feel it’s super strange that it has such a tiny threshold where it feels like the front end might come undone and then it disappears at 40. Any thoughts would be appreciated !

 

Cupped tires?

 

If anything it’s got edge wear- used to be a hunting/farm truck so that makes sense.

I’m going to get them balanced now and see if that makes any difference!

 

I didn't see alignment in your post, have that done while you're at it.

 

Sorry forgot to mention but yes alignment as well after replacing the rack last month.

 

Did you align the drive shaft back like it was before you took it apart for the Ujoints? That will cause a vibration if you didn't.

 

I did, had the bad vibration and saw the carrier bearing was completely shot so thought that must be what’s causing it, so I decided to order u joints and get them all done at the same time. U joints were actually not in bad shape at all, but I did them anyway with carrier bearing, marking all the points of separation.

But, it didn’t solve the vibration.

 

Do your research on this https://eastcoastgearsupply.com/i-8...BZyDGqzY1ZhZ3Y-zrbVGGdiPYUuA0q7rWYZgkvlJV3TNh

Some have said it helps. There are many posts regarding this on the forum.

 

For anyone in the future who might need this- the vibration was solved. I needed to drop the center bearing down a couple inches to get a better angle on the double cardan joint and the angle going into the rear dif