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Front derailleur cable routing: lesson to share...

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Front derailleur cable routing: lesson to share...

Old 03-12-06, 06:55 PM
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Front derailleur cable routing: lesson to share...

Yesterday I installed a Shimano 105 front derailleur on a bike I am building up. I had previously installed a Shimano Ultegra triple crankset on this bike and Shimano 105 STI levers. With the front derailleur cable routed under the bottom bracket I attached it to the derailleur and adjusted the low and then high limit screws on the derailleur. I had previously adjusted the height of the derailleur above the largest chain ring and the alignment of the derailleur cage with respect to the large chain ring.

Assuming I had everything adjusted, I turned the cranks with one hand and began pulling the shift lever with the other. The chain trimmed towards the middle chain ring, then moved onto the middle chain ring, then trimmed towards the large chain ring... and then... would not move onto the large chainring.

I pulled the lever and the derailleur's cage moved towards the big chain ring but the lever would not "click into" position. When I released the lever the derailleur moved back towards the middle ring. I thought the derailleur was hitting the high limit screw so I checked this multiple times but that was not the problem. Even with the high limit screw backed way out the indexed shift to the large ring would not complete.

Today I searched bikeforums and was not able to find mention of this same problem (hence this post). I went to Shimano's web site and went through the installation instructions again. I made the realization that the way I attached the cable to the front derailleur was not as they depicted. The difference is subtle and I wish they had warned against the improper method. See the attached image, I originally attached the cable as shown in red.

After changing the routing to match the installation instructions my shifting problem was gone. I did not revert back to the incorrect method to check, but I bet the cable had been getting caught up on the derailleur's mounting bracket or linkage as the derailleur tried to move out to the big ring.

Hopefully somebody saves themself some frustration by reading this post!
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thomasbien is offline  
Old 03-12-06, 07:31 PM
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Good post. I'm sure it will be helpful to someone.
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Old 03-12-06, 07:42 PM
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Excellent warning and you aren't the only one to make that mistake.

I installed my 9-speed 105 fd cable exactly the way you did and, while the derailleur would shift to the big ring, I was getting chain rub way too soon in both the large and middle chainrings. I couldn't use the largest 4 cogs in the big ring and the smallest 4 in the middle ring without the chain hitting the cage and no amount of adjustment would improve the situation.

I knew something was wrong but not what until I looked at the installation sheet very carefully and found that I had run the cable incorrectly, just as you did. I rerouted the cable and the problems went away. It was hard to believe that small an adjustment would have that big an effect but it certainly did.
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Old 11-14-17, 09:50 AM
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Thanks, and sorry for the tread resurrection but a search brought me here. I was putting new cables on a Trek 560 Pro last night and the "correct" routing was what I ended up doing so there would not be interference between the cable and the derailleur spring. I was doubting my choice all night long and into today. This was very helpful!
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