goldfinch

Friend front deraiileur broke--the little tab that holds the spring. It is a 3 x 9 road bike, had a tiagara front derailleur. I tried a Sora and and 105, both for 3 x 9 configeration. No matter what, I cannot get a big rig shift. If the limit screws are far enough out it drops the chain. If in enough it scrapes the chain. Suggestions? I have fussed with rotation et al.

fietsbob

indexing? shifter may be to blame , actual FD is pretty simple .. [ height, rotated in line with chain ring and stroke limit screws ]

When are you requiring the shift? early or late , all chain tension off?


looked for videos on the topic?

Retro Grouch 

In general, whenever I've encountered a front derailleur that was fussy, the position of the derailleur on the seat post (height and clocking angle) was the problem. In your case, I'm doubting that's the issue since you said you have checked that so carefully.
#2 . Check your cable routing. the cable is supposed to go OVER the little finger on the derailleur. That changes the angle of the shift cable and makes more difference than I'd think it would.
#3 Make sure that when you set the cable tension that the derailleur and shifter are both in the small sprocket position.

What are you using for a shifter? I'm told flat bar shifters have a different cable pull but, since it was working with a Tiagra derailleur I'd think it would work with a Sora.

redlude97

Does the FD match the chainring sizes? Shimano has used some combo of 52/42/30 and 52/39/30 and 50/39/30 over the years and the front cage needs to match those sized rings. Height is also extremely important due to the cage shaping. Best to match the crankset, FD, and ****er models

79pmooney

Yes to the above re: angle on the seattube & height. I set my FDs to clear the chainrings by ~1mm at the closest point. I also have no qualms bending the forward tabs of the cage in, ie outboard plate tab in and inboard plate tab out. (Bending the tabs isn't possible on all FDs.) Another trick - remove the small bolt and bushing at the back of the cage and replace it with a hardware bolt and a stack of tiny washer shorter than the bushing you took out.

All of this will add to chain rub and more need to trim the FD while riding but your shifts will get faster, more positive and there will be less throwing of the chain in either direction.

Ben

goldfinch

If I set the Sora derrailleur high, higher than the millimeter or two that is generally recommended for clearance, I can get to the large ring. But, It isn't far enough out to avoid scraping the chain and further out scrapes the pedal . Weird. I am going to try the my old 105 der again as it has exactly the same angle as the tiagra. But I am not hopeful. This is a first for me--I might end up sending him to a real mechanic.

goldfinch

Think I will try this on the old 105 I am going to try again.