2003 SP 700 – Rear bearing came apart

Hello everybody,

Today I replaced my left side rear axle with an OE style complete axle assembly from ATV Parts Connection.

Everything went fine until I tried to slide the hub onto the axle splines and inside the bearing. It did not want to slide in. I thought I might have put too much grease on the splines (and also on the sleeve of the hub that goes inside the bearing), so I tried to tap it in with a rubber mallet. It did go in about an inch, then I thought it does not feel right.
So I tried to pull the hub back off, and it came off quite easily – with the bearing’s inner race stuck onto the sleeve!

The inside part of the bearing looks OK, all the balls are held in place by grease, so I pushed/tapped the hub all the way back in, then tightened the hubnut and installed the wheel.
When I tried to spin the wheel it felt a bit grinding, but the sound went away. When I try to push the ATV in neutral back and forth, there is no sound coming from the bearing area.

I am thinking that it would be probably a good idea to replace that bearing, anyway – I just want to hear some opinions on what could have caused this?

Why did not the hub slide on like it was supposed to? Could too much grease on the splines of the axle cause this?
(I don’t even want to think that the sizing of the splines of this OE axle is off a little bit…)

Could the "tapping the hub on" have damaged the bearing so that it got separated? (I was not using really too much force).

Just wondering what everybody thinks.

Thank you for all ideas in advance!