Gear in differential case slipped out
 

I have an 89' F-250 with the 10.25" rear end. I slid the pinion shaft out and the top pinion gear slid out. It doesn't want to go back in. It is engaged with both side gears but is off center and spins in place. Anyone have any bright ideas? Is there a trick to get it back in position for the shaft to go back in? Any help would be greatly appreciated.