Fergulus

I have a used Diamondback S-30 that has been working just fine with minor derailleur adjustments every few months. In the past two weeks however my chain has derailed off of the front sprocket over 5 times. This has happened mainly when I am at a standstill and waiting for an opening in traffic, or am getting onto the bike for the first time. Luckily I hear or see the chain is off before I apply pressure and snap the chain.

My front derailleur is always on 3rd gear, and is tensioned just so that it does not grind, even though it takes a long time to force it into third. Even so, the chain derails off the outside and gets stuck in the pedal bar. I have also noticed upon getting back on the bike after parking that it has moved to 2nd gear for some reason. If this was happening on a trail I would understand it's from vibrations, but this is always after I am stopped that it derails!

Any help would be greatly appreciated, and if I have forgotten to mention an aspect please let me know, as I am new to these forums.

gyozadude

You may want to do a web search on "Sheldon Brown Derailler Adjustment" and read up on his pages describing how to set them and limit their motion and perhaps tighten the fixing screws on the shifters. Also, if you are cross chaining, that's a no-no and may aggravate misadjustments in your FD.

zukahn1

You should check to make sure the bottom bracket is tight and properly adjusted this can often cause front derailer propblems.

reptilezs

bent tooth, fd tail in/out