in middle of hub there is a ring which clips both bearings together, it will have come out of its grooves you will have to take hub off and refit clip into it's grooves and when you fit hub assy to axle it needs to be dead square to stub axle when you put it back on [its a bit difficult with weight of disc -it may be easier to get assistance to lift it on].hope this helps.
k, April 2010