Bicycle Mechanics - Rear derailleur wobble

Hey all,

I was adjusting the indexing on my rear derailleur and couldn't seem to get the chain to work smoothly. From the back it looked slightly off from vertical, so I checked the derailleur hanger but it's fine. Then I noticed that when I tighten the bolt that attaches the derailleur to the hanger, if I tighten it all the way, the derailleur ends up not vertical. If I back off the bolt, taking the derailleur out, the derailleur wobbles relative to vertical. I can get good indexing if I back the derailleur out a couple of turns and eyeball it to be vertical.

This wobble with bolt turning during installation also occurs with the same model derailleur on a brand new frame. Is this by design? Do I need to worry about my derailleur flying off since it is not tightened all the way down?

Thanks!

Take the bike to a shop and have them check the derailleur hanger. It doesn't have to be bent very much at all to throw your shifting out of whack.

This sounds like the bolt that connects the der to the hanger is bent or has some damaged threads. You shouldn't use it without the bolt being tightened down all the way. It can pull out and tear all the threads out of your hanger.