Rearend Rebuild, Need Help

O.K., I got the pinion and the yoke together. When the case is sitting on the ground with the yoke on top, am I supposed to be able to lift on the yoke and pull the yoke and pinion up and down a tiny bit or is there supposed to be no movement in it exept for the rotating. When I pull up on the yoke, I can move the pinion up and down inside the case.