Hi,

The shaft needs to move from left to right (sliding in and out from the
velocity joint)
It's also important to adjust the boot each side (they act like a spring)
so they have about the same distance each side. (Align with notches on the
shaft)

Did you disassemble the velocity joint? They can easily be reassembled the
wrong way.

http://pages.infinit.net/engine/cv_joint_maintenance.htm

But if you are running the van right now they are probably the right way.

There is now way that the shafts would not move (left to right) if
reassembled the right way. Maybe one small parts is looses or offset????

Ben