My mechanic has given up; but I'm hoping someone out there has some idea what happened here:
1. Replaced the SRAM chain on my bike. SRAM Red front derailleur, XX rear. 34/50 on front, 11/32 cog in the back. There were NO problems shifting, but the chain measurements were indicating some stretch had occurred.
2. I began to experienced the chain "locking up" (I guess this is called "chain suck") at least once on every ride. I examined the chain, wiggled every link to check for a stiff one (didn't really find anything), and lubed it. Everything was great for 1 ride, then the problem returned.
3. Installed a chain guard to prevent the chain from coming off on the inside. This made no difference. The chain still locked up. Slow back-pedaling would unstick it.
4. My mechanic shortened the chain by one link and installed a new 34 chain ring.
5. Now, in addition to the chain lock-up, the chain falls off on the OUTSIDE, usually once on every ride. Usually I'm just on a straightaway, somewhere in the middle on the rear cassette, and shifting from the small to the big ring in the front. Not putting much pressure on at all.
Are there any hypotheses on this? Any input is appreciated. My mechanic is stumped; now wants to replace everything: chain rings, cassettes, and the new chain itself. I hesitate to do so unless I know what's wrong.
Thanks for your ideas...