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shimano 105 Front Derailleur won't shift to lower sprocket

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shimano 105 Front Derailleur won't shift to lower sprocket

Old 08-31-11, 06:12 PM
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thesignguy812
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shimano 105 Front Derailleur won't shift to lower sprocket

I've noticed in the last few days of riding (Trek Road Bike) my front deraileur won't shift to the lower front sprocket. When it first started happening a bit of pressure with your fingers on the deraileur was enough to make it move and then work just fine every time.

Now, It shifts the chain to the large sprocket but won't shift back to the smaller. You have to push with your fingers every time.

All I've done is clean and wash the bike and lube the chain lightly after.

Help please , how do I fix this?

Last edited by thesignguy812; 08-31-11 at 06:15 PM.
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Old 08-31-11, 06:44 PM
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desertdork
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Check the FD return spring to make sure that neither the spring nor the tab it rests against is broken. Otherwise, you may have either (1) a grungy FD return spring or (2) friction somewhere in the cable run. The FD spring can be flushed out with your choice of solvent/cleaner (wd40, Clean Streak, GT85, etc...) and re-oiled. If it's not the spring, check to see if operating the shifter produces slack somewhere in the cable. If the cable becomes slack along the down tube, and the derailleur fails to move normally, the bottom bracket cable guide may be grungy or otherwise in poor enough condition that it prohibits the cable from moving smoothly along it. If you have brifters, a stray cable strand could possibly be snagging the interior of the cable housing. And if you have brifters, and you no longer get a positive *click* when shifting, you might have a shifter issue.
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Old 08-31-11, 07:19 PM
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thesignguy812
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Thanks. Will look at tomorrow and let you know.
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Old 08-31-11, 07:23 PM
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Same thing happened to me. I first ensured the cable stop was seated correctly in the shifter, then sprayed the heck out of the shifter body with solvent. When these failed I took it to the LBS where I bought the bike. They spent a day or two, the gave up. Luckily, I was 3 weeks short of the Shimano 105's 2 year warranty period. They stood by the product and replaced it.

Last resort, but this seems to be known and common failure mode of the STI shifters.
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Old 08-31-11, 08:39 PM
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If you have the earlier 10-speed 105 shifters and a double crankset you may have a warranty issue. The earlier 105 10-speed left shifter was meant to be used with a double or triple but when used with a double had a tendency to "lock up" when shifted into the big ring position. The later 105 shifters are double or triple specific and in some cases Shimano has replaced under warranty the earlier shifters with a double only shifter.
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