So I'm taking the time during the holidays to overhaul my commuter bike. The whole drivetrain was full of old oil, road salt and grime so I decided to take the whole thing apart starting with the back wheel. Once I got it off, I ended up with half of the rear axle in my hand and a bunch of ball bearings on the floor (I found them all eventually).
The bike has been in use for about 18 months, and there were no rust and plenty of lube inside the hub so I don't really think it's natural wear.
What could have caused the axle to break? My theory is that they pulled the nuts too tight when they built the bike.
More importantly, is this a "user serviceable part" or do I need to get it repaired/replace the wheel? Seems to me getting the ball bearings to stay in place while I insert the axle would be quite challenging.