Originally Posted by
Retro Grouch
Check out where the cable attaches to your derailleur. Many Shimano front derailleurs have a little L-shape arm. The shift cable goes OVER that arm.
+100. This is a very common mistake. If you route the cable under the "arm" ( a little tab) so it goes betwween the tab and the bolt it will not pull sufficient cable. The cable must go outside the tab and attach over the top of the bolt. Shimano's installation sheet shows the proper routing but doesn't emphasize it enough.