Help me troubleshoot front derailleur problem

[yoshirider]

The chain recently got stuck between the front derailleur cage and one of the chainrings so I loosened the braze-on bolt for my SRAM Force front derailleur to get it unstuck. Now whenever I shift to a larger cog in the cassette sometimes the chain drops from the big chainring to the smaller chainring. What could be causing this? Here's everything I've tried:

1. Checked the chain for stretching wear - passed
2. Tightened the braze-on bolt to 6Nm (helped a little bit)
3. I haven't touched the limit screws at all

[djdj]

I would rest the cable and limit screws. If that doesn't work, check the shape of the cage against spec -- the incident may have bent the cage.

[cachagua]

Has the shifting changed since before the incident? If not, that would lead you to look for something besides the derailleur.

Did a tooth or two on the big ring get damaged in the incident? That could cause the chain to shift down when you go to bigger cogs in back regardless of what the derailleur's doing.

And if the shifting has changed -- what's it doing wrong?

Guess I should ask -- I got the idea from your description that the chain just spontaneously falls off the big chainring, is that correct? If the derailleur actually pushing the chain off, that's a different problem.

[oldpotatoe]

The chain recently got stuck between the front derailleur cage and one of the chainrings so I loosened the braze-on bolt for my SRAM Force front derailleur to get it unstuck. Now whenever I shift to a larger cog in the cassette sometimes the chain drops from the big chainring to the smaller chainring. What could be causing this? Here's everything I've tried:

1. Checked the chain for stretching wear - passed
2. Tightened the braze-on bolt to 6Nm (helped a little bit)
3. I haven't touched the limit screws at all

Sounds like a good old fashioned front der adjust is called for...proper height and alignment with regards to chainrings..sounds like it may be too much 'tail out'..

[yoshirider]

Thanks for the help guys. The dropping to the smaller chainring only occurs when shifting to a bigger cassette cog. It didn’t do this before the loosening of the braze on bolt. The chain only got stuck because I was trying to put the rear wheel back on with the bike upside down and I wasn’t paying attention.

I guess I’ll try to realign the front derailleur and check the screws. Hopefully this is easy? I’ve watched YouTube videos but never actually tried to adjust on my own.

[oldpotatoe]

Thanks for the help guys. The dropping to the smaller chainring only occurs when shifting to a bigger cassette cog. It didn’t do this before the loosening of the braze on bolt. The chain only got stuck because I was trying to put the rear wheel back on with the bike upside down and I wasn’t paying attention.

I guess I’ll try to realign the front derailleur and check the screws. Hopefully this is easy? I’ve watched YouTube videos but never actually tried to adjust on my own.

Or, spend $10 or so and have decent LBS do it..probably as a walk-in..

[cachagua]

Or if you want to teach yourself about it, just put the bike in the stand (bungie it from the ceiling, whatever) and shift all around and watch what happens. Just observe. Listen to the chain all the way around, examine the chainrings, look at the chain's location inside the cage in this and that gear position... you may see some problem that you can take care of easily, just by twiddling a screw or tightening the cable.

If you mess with it all you want to and can't make it work to your satisfaction, you can always walk into the LBS and pay the $10 afterwards. I'd encourage you to see how far you can get with it, if only to inform yourself.

Every bike mechanic, even the heaviest-caliber ones, began this way.