I had a mild spill today on my new bike, which put the (Tiagra) derailleur cage a little bit out of line. With some bending and eyeballing, I got the two jockey wheels lined up 'almost' perfectly parallel with the cassette, and shifting is okay.
My problem is, when I shift down to about the 3rd largest gear and larger, the cage 'ticks' when pedaled about 240 degrees (not in the same spot, just after about that much pedalling). I watched the cage and what's happening is, the chain starts to drift to the right (outside) of the lower jockey, and then, for some reason, one end of a link rises up off the jockey, and the cage pulls back a little bit like it's trying to get in position for a shift. It doesn't go far, though, and by the time the bunched link gets off the lower jockey, it loosens up and the tension drops out of the cage, causing it to relax into position again.
None of this happens on smaller gears. What's going on here? Can I fix it without shelling out cash for a whole new derailleur (was basically new)?