From my past experiences if the hub does not click in place. Rotate it while pushing forward once it grips the splines are lined up. Then What I do is hold on hand on the inner hub pressing into the tranny I pull the shaft back a little stretching the boot slightly then I jolt the shaft back to the hub that little bump or clunk should be plenty of knock to lock it in place. If not take the shaft out and make sure the old snap ring was not stuck in there. If not check the new snap ring and ensure the that it is not bent otherwise it will not fall in the groove flush. Next I have noticed on some snap rings that the ring gap is to wide making the ring hit the splines to flat. I had to take some channel locks and bent in the snap ring some just enough to make it a little smaller then try that. Hope that Helps
