Check where the derailleur is clamped to the seat tube, both in terms of alignment on the axis and vertically up and down the tube. If it is twisted back and/or riding too low, that would be problematic.
2011-11-10 23:23:36
9
derailleur troubles
So today, I was shifting down while pedaling, and suddenly my chain stopped. I checked it out, and it was caught on the cage part of my front derailleur. I fixed the chain, but the cage is all bent and stretched now. is there anything I can do to fix this? What's happening now is that the chain is rubbing on the right side of the thing.
This is what it's looking like
2011-11-10 22:42:46
It doesn't appear to have moved at all. I tried to move it a bit and unscrew some of the parts, but it wouldn't budge. I tried to stop pedaling as soon as I felt the resistance, so I'm not sure if it would've had a chance to twist? I'm completely lost on this one.
2011-11-10 23:40:24
Did the cable snap? (it may be broke inside the housing) Try moving the gear selector and watch to see if the deraillier moves at all. If there is no cable tension the spring on the deraillier will pull it to one side.
2011-11-11 01:28:33
You should probably bend the cage back into place, carefully, then make sure the problem that caused the chain hangup in the first place is solved. It sounds to me like the derailleur is too close to the chainwheel, probably because it is mounted too low.
2011-11-11 15:37:33
hm, the derailleur moves, but I have to stay one click above where I want to be to avoid rubbing.
I think it might have gotten better today, but sometimes my imagination plays tricks on me, heh.
2011-11-11 20:09:42
I bent a middle chainring a few weeks ago. At first I thought the deraillier was bent and then I figured out it was the chainring causing the rubbing.
2011-11-11 20:24:49
I hope it's not the chainring, those are brand new 
2011-11-11 20:46:09
if it's the chainring, it will only happen during a portion of its motion. if it's a constant scraping, it's a derailleur adjustment issue.
2011-11-12 17:30:01