8.75 Not centered?!?!

With the axle and tires centered you tighten the the u bolts an the axle shifts sideway?
When the springs and perches are snugged equal distance from the housing ends, and positioned close (no offset hangers yet) to where they will bolt, the wheels shift to the right. It's as if there's not as much room on the passenger side but I can't see a measurement discrepancy?