I have been given a bike for free, as the rear wheel was very wobbly.
I'm been learning how to take things apart, and investigated the axle - it's not bent.
The ball bearings, however, were a surprise. There were 9 on one side (the side of gears) and none on the other side. Those 9 balls were kind of loose (I think 10 could fit well), and there was a smashed up steel ring in there.
I'm not sure if that's something "useful" (eg, reduces friction?), or if it's the "dust cover" that got pushed in and smashed thinner. I found it weird that only that side lacked a steel dust cover.
Could you help me understand if this was just a bad maintenance job (the rear wheel is clearly newer than the front one) or if it makes sense to have ball bearings only on one side?