infuriating shifting problem
Hi everyone - I have a 2003 Enduro Pro with the XTR shifter/brake lever combo. Recently this bike has begun randomly throwing the chain off of the middle chainring to the inner, or occasionally all the way off to the inside. I completely adjusted the front derailleur, cleaned and lubed, etc., to no avail. The teeth on the chainrings are straight and not badly worn, and my LBS checked the chain itself about 3 weeks ago and said it was fine. I have also checked the frame for cracks, but havent found any. This does not happen too often when the bike is in the stand, when I ride on pavement, or when I am climbing on a trail. It happens mostly in relatively smooth, flat areas, and in bumpy small terrain, like roots or baby head rocks. It does not happen when I go over something large. It does not happen much on descents, though living in Indiana maybe that is because there aren't many descents to begin with.
When this occurs I can usually get it back into the middle ring where it will ride for as little as 10 seconds or as much as 10 minutes before repeating itself. What could it be? This is killing me at races and is becoming more and more frequent!
Thanks for any help!