Front shaft vibe question

[96country]

OK. I just installed control arm drop brackets on the XJ. I pulled the front driveshaft prior to starting the install to check the U-joints and stuff, thinking that it might need to be lengthened. After I finished the drop brackets, I test drove the XJ on the highway and it was nice and smooth. I put the front shaft back in and it seems like it's long enough, but I get pretty bad vibes at anything over 60mph. It had no vibes before the drop bracket install and I added no lift. The pinion angle is even much better now. What do you think it could be?


Here are a couple of pics of pinion angle and the amount of slip in the shaft.

 

[old_man]

By pulling the splined portion of the front shaft out so far, you allow the shaft to flex at that point, hence the vibes. Either move the axle rearward some or lengthen the drive shaft.

 

[96country]

OK. If I have the DS lengthened, how much slip should be showing?

 

[old_man]

Cycle the front suspension and see how much the slip yoke moves. Then just make sure that the shaft is just short enough not to bind. Many times with changing the arms, the front shaft ends up not changing length too much over the range of motion. It looks like 1.25" - 1.5" would be about right, but check it.

 

[96country]

Well, I went ahead and took the shaft apart at the splines. Seems like it is a bit short and not getting full spline engagement. On level ground the joint to joint length is 33.5". Here is the shaft layed out with that distance between the joints.