Bicycle Mechanics - Shimano 105 front STI shifter problem

Hi everyone

I just upgraded to 105 10 speed STI shifters on a bike that was originally a 7 speed downtube shifter system with double chainring. Things I changed to 10 speed 105: shifters, free hub (actually changed the whole wheel), cassette, rear derailer, chain. I did not change the front derailer and chainrings. The new 10 speed rear gears work fine but I have a problem with the front gears.

The front STI is double and triple compatible. As I have a double, I should only need to make one shift but this does not complete the shift to the large chainring. It only shifts when I do the second shift. Effectively, it acts as if I have a triple and I have to shift from small to "middle" to large to complete the shift instead of just one shift from small to large.

The problem cannot be caused by the following: I am not confusing a trim click as a shift (there is no trim click on the large lever anyway). There is no slack in the cable when on small ring and is routed correctly over the tab on the derailer. The low limit screw is set correctly and the inside of the cage barely clears the small chainring. When I make the first shift, the cage does move the chain quickly but just not far enough to mount the large ring.

Questions:
1) What else can it be and how can I fix this?

2) Is this simply because the spacing on a former 7 speed chainring is just too wide for 10 speed STI front shifter so I just have to live with making 2 shifts?

3) If I can't fix it, will it damage the STI shifter to shift twice to make a single shift from small ring to large? The instructions warned against shifting to the third position on a double.

Thanks

Is your front derailldur a modern "road derailleur". In other words, is the cable pull arm above the pivot screw about half the length of the arm between the screw and the cage or is it about the same length. If the latter then you have the wrong "ratio" in the front derailleur to work with STI levers and will need a new FD. Might not be the problem but the check is quick.

edit: this is the same symptom as when running an MTB front derailleur with road shifters.

I've had similar problems and have made it work by attaching the cable to the opposite side of the FD attachment stub. This makes it move a tiny bit more on the shift. I also normally need to move the dérailleur slightly nonparallel in relation to the chain rings.

I might try using a triple FD next time since it's really no different than having only two of three chainrings.

What you describe is perfectly normal. Every brifter is a triple, so you have to go all the way to the last click when shifting up to get the big CR and all the way down through all the clicks to get back to the small CR.

When shifting to the big ring you should shove the brake lever all the way to the right. Pay no attention to where the detents (click stops) are. They have no real purpose on a double. Shift all of the way to the right for the big ring, all of the way to the left for the inside ring. 105 has detents for use with triples. 10-speed Ultegra and D-A double shifters don't have these.

Al

Is your front derailldur a modern "road derailleur". In other words, is the cable pull arm above the pivot screw about half the length of the arm between the screw and the cage or is it about the same length. If the latter then you have the wrong "ratio" in the front derailleur to work with STI levers and will need a new FD. Might not be the problem but the check is quick.

edit: this is the same symptom as when running an MTB front derailleur with road shifters.

Thanks for this explanation. It looks like I do need a new derailleur. The one I have is an old road derailleur (RX100). The arm lengths are pretty similar...just over 2 cm above and 2.5 cm below...far from being half the length.

The problem still happens even when I changed the cable routing to under the tab and even when I push the lever all the way across, ignoring clicks. I have to push all the way across twice. I even turned the derailleur round a bit to give more of an angle to the cage which helped a bit but not enough to allow one push.

I think a new derailleur is called for. It seems upgrading one thing always leads to another thing. I hadn't planned on a new rear derailleur either but it turned out the 7 speed old one wouldn't move far enough to reach the largest sprocket.