Rearend Rebuild, Need Help

Hey guys, I have taken the 3.23 gears out of the 489 case and cleaned them all up, and replaced the bearings and races. I am trying to put this thing back together but I've got a problem. I am using the same yoke and pinion that I took out but now, I cant get them to go back together. I even tried to beat the pinion into the yoke with a hammer and a block of wood but it doesn't work, the pinion still only goes in so far then stops. Am I doing something wrong? Does the pinion only go into the yoke one way ? How do I get these two back together?