rear derailleur question
 

I have an issue with my RD/chain, which seems to have started after I took a little tumble. When I am cruising in my big ring, with any gear out back, the chain seems to catch on the lower pulley and rotate the derailleur forward, then releases and makes a scary slapping sound as the chain tension and spring in the derailleur pulls everything back to normal. This does not happen in my little ring.

The chainring is new-ish, the chain and cassette are pretty new. The alignment of the hanger appears proper . I'm thinking it's a sticky link, and/or pulley....Or a slightly bent derailleur cage? Cable tension seems fine, I can reach all the gears without trouble. I must say, the derailleur is low-rent, and can attest that it has some slop built into it - Shimano Deore, Mega 9.

Anything I'm missing?

Details: 38x42 up front, with 11-34 out back. 9 speed cassette and chain, shifted by bar-cons friction style. I never cross chain with 42x34, only up to 26 or so. The chain is perhaps 2-3 links too long.

you took a 'tumble' I do hope you are ok. I assume you fell to your right? check vertical alignment of your rear derailluer. the hanger or the cage could be bent inward or the cage twisted. it may even be as simple as dirt or something in the cage.

You should stop riding until you fix this problem. If the chain fails to exit the derailleur it can twist the derailleur off the bike and possibly damage the frame stays.