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Front Derailleur Ghost Shifting

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Front Derailleur Ghost Shifting

Old 05-17-16, 04:22 PM
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old_dreams
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Front Derailleur Ghost Shifting

Quite often the front deraillleur on my bike will downshift from the big chainring to the small. It's a double setup. At first I thought I must be hitting the brifter by accident but it even happens when I am in the drops.

Brifters are 2011 centaur and the FD is 2010 Centaur.

I have googled this to death and can't find anything similar.

Could there be a problem with the brifter. It's almost like it occasionally can't hold the cable tension and the mechanism slips.

I'm certain it is not any of the following
- cross chaining
- frame flex
- stiff link
- derailleur adjustment. I have it adjusted pretty much spot on. Shifts are quick and precise.
- chainline
- worn chain or rings. Was happening with low kms on bike
- me clipping the derailleur with my foot.
- cable getting pinched or overlapping rear der cable

When the chain is on the big ring I have tried to push the FD in with my fingers and it doesn't budge.

Any ideas?
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Old 05-17-16, 10:56 PM
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Bike Gremlin
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If cable goes beneath the BB, is there a cable stop installed at the bottom?

Or is there some housing movement? Some housing stop failing? Then when you shift back to smaller chainring, cable loosens and housing falls back into place.

If you checked already what you said you're certain of, do check cables, housing and routing.
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Old 05-19-16, 01:31 AM
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No cable stop at the bottom. Cable is routed under the bottom bracket through one of those plastic guides.
But your question reminds me that I did notice previously that before the cable attaches to the FD it travels quite close to a bolt on the FD. So it might be getting snagged there during a shift up to the big ring. And then if it unsnags the cable tension will be lost. Something to check. I might try to fit something to rule that out.
Thanks for replying.

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Old 05-19-16, 12:12 PM
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Well scrap that idea. When I shift up to the big ring the FD spring & cage moves away from the cable so it's not going to get snagged.

There's only one cable stop apart from at the brifter. That is the one near the top of the down tube. That stop looks to be seated properly and theres no movement there so I don't think that's to blame.

After routing under the BB the cable does travel through the frame a little way. Can't see anything in there that might cause a problem.

I'm back thinking it's the brifter.
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