Shimano Ultegra STI Shifter downshifts only when returning to start position
I am having an unusual problem with my STI shifter where it downshifts after a 'click' (doesn't actually click but I can't push the lever anymore) when returning to the start position when I use the downshift lever on my front shifter. This only occurs when going from the top most gear to the next gear position. Also, this is occurring when the shifters are off the bike and aren't attached to any cables. Thanks for all the help.
Any excess friction in the cable housings or cable routing can cause this but you said it act the same off the bike. Dirty or corroded hinge pins in the derailleurs can also cause excess friction, but again, that would be on the bike.
Also, this is occurring when the shifters are off the bike and aren't attached to any cables. Thanks for all the help.
This indicates that the problem isn't cable friction. Sometimes the front shift cable frays inside the shifter, so make sure that the cable anchor and shift barrel are clear of any bits of old cable strands. Then, if flushing doesn't work (I use Tri-flow in the aerosol can), you probably need a new shifter. The ratcheting mechanism of front STIs is usually the first component to go. Proper hygiene and adjustment prolong life.