105 Front Shifter Downshift issues
 

Hi all - I'm in the final stages of my new buildup and was going to adjust the shifters/derailleurs when to my surprise my front shifter wouldn't work. It's a Shimano 105 (5600) that I bought off eBay sold as new bike takeoffs, so they shouldn't be worn out. The right (rear) shifter works like a charm but the left (front) wont downshift when there's tension on the cable, which is any time you want to down shift. If the cable is slack, as in not connected, it downshifts just fine. I searched the forums and found people saying to hit it with spray lubricant inside, I did this and still no dice. Anyone know what's wrong with this unit? How to fix it? Any and all help appreciated, Nick

Your shifter cable is too tight. Set your front derailleur stops and then take a little tension off the cable. When I first started building bikes I made the same mistake more than once. If you have too much tension on the cable it binds up the shifter and it won't release properly.

A trick I use now is to turn the barrel adjuster all the way in, then back out one full turn. I then stretch the cable tight and tighten the bolt down on the derailleur. Once that's done, I'll screw the barrel adjuster back all the way in. That will put a little slack in the cable and allow you to downshift more freely. Fine tune your shifting with the barrel adjuster so that it picks up on the larger ring readily, but not too tight.

To set your front derailleur stops, shift the front into the small ring and the back into the largest cog. That should put your chain line all the way in closest to the bike. Then use the Low side adjuster screw and set the derailleur so that the chain neither falls off to the inside and doesn't rub and make noise on the cage. I usually shoot for about <2mm of gap between the cage and the chain. Then shift the front to the big ring, and the back to the smallest cog. That will put the chain line out furthest from the bike. Using the High side adjuster screw, set the derailleur so that the chain doesn't fall off to the outside and doesn't rub on the derailleur cage.

Walt

P.S. Tightening the adjuster screws moves the cage towards the rings, loosening the screw moves it away from the rings. Works like that for high and low.

Thanks for the tip. I'll give that a shot and see what happens

In other words, what's happening is that the derailleur is hitting its high gear limit stop before the lever has finished its motion and the ratchet has clicked in, so you end up putting extra (and useless) tension on the cable to complete the lever motion. It can take a bit of trial and error to get set up because you're tightening the cable clamp at the start point of the motion, trying to get the end point in the right place. That's why the barrel adjuster is so useful... as BFW recommended, although I would set the small ring stop screw before tightening the cable clamp.