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Front derailleur shifting problems

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Front derailleur shifting problems

Old 10-03-12, 01:23 PM
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spivonious
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Front derailleur shifting problems

Hi All,

I did a search through the threads here and didn't find any that sounded like my situation.

I've been commuting on a Trek 7300 for a few weeks. Lately (last week or two), it has become increasingly difficult for the chain to "catch" when moving up to the big ring on the front. As far as I can tell, the derailleur is adjusted properly, in that it moves the proper distance away from the frame and the chain makes a lot of noise rubbing against it and the chain ring, but it doesn't seem to grab.

Sometimes, I can make it grab by pedaling backwards a bit and then forwards. Other times I can get it to go by changing gears in the rear while trying to get it to shift in the front. Still other times, it shifts perfectly fine.

Any ideas? Do I need to raise up the derailleur? I've tried adjusting the limit screws, but of course it always shifts right on the bench.
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Old 10-03-12, 03:25 PM
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cny-bikeman 
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Looking for a particular situation to match yours is less fruitful than looking at the proper mounting and adjustment for a front derailleur and first making sure your derailleur meets those criteria. The front needs to be at the proper height and angle to the chainwheel, with proper inner/outer adjustment and reasonably low cable friction. If you did read any of the front derailleur threads you may have seen similar to the following:

Go to http://www.parktool.com/blog/repair-...ur-adjustments and follow the directions from start to finish, skipping no steps.

Do that!

IF you do so and STILL have the problem try to determine if your derailleur cage has been bent, also check to make sure the inside of the cage has not been scored by the chain. A derailleur or chain that has developed side flex from wear can also degrade front shifting. But everything works worse if the derailleur setup is not proper, so do that no matter what.
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Last edited by cny-bikeman; 10-03-12 at 03:34 PM.
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