The hub sliding off is a pretty serious thing. If you think everything fits well and parts are in good shape then something is missing, perhaps that large snap ring in the hub.

I wouldn't try anything until after you put up some pictures and get some more eyes on the problem.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-