Originally Posted by
HillRider
I've never had the limit screws on any derailleur change spontaneously but I did have a rear derailleur ( a week old Ultegra 9-speed!
) destroyed when the chain grabbed a piece of steel wire thrown up by the front wheel and ran (or tried to anyway) it through the derailleur. Fortunately, only the derailleur was trashed and the dropout was ok.
I agree. Limit screws don't creep. I've never run across one that isn't tight in the derailer body.
Why when something happens with a derailer, the very first thing that people start talking about is the stupid limit screws? Limit screw problems are the last thing that goes wrong with a derailer. Once set, the limit screws will never be a concern again.
bobthib, I assume that when you say the "chain came off" that it came off the chainring. If this is the case and the drivetrain was under tension, the sudden release of pressure on the chain could have caused the spring in the derailer to go backwards. If you were under a fair amount of tension, such as taking off from a light, the release could be violent enough for the derailer backlash to carry it up into contact with the cassette. Once there, the derailer could be twisted around the cassette and mangled.
It sounds complicated but if you shift a bike on a stand you can see the derailer bouncing around a bunch when you shift off a ring...especially the big one.