2

To avoid chain rub on the inside of my derailleur when in the smallest chainring and in the biggest cog on the cassette I've turned the L-screw out / counter clockwise. Now the rub is gone but due to the angle the cable is pulling the front derailleur it is nearly impossible to get into the largest chainring.

Turning the L-screw in a bit more pivots the derailleur into a more horizontal position so that the force of the pulling gear cable is no longer towards the derailleur's center of rotation and thus can actually move the derailleur.

To fix this I'd probably need to either get the cable to pull from a position closer to A or at least to somehow generate some force towards A.

The other solution would be to turn the L-screw in again and avoid the chain rub in a different way.

How do I do that?

Tried:

  • I've already tried to move the derailleur on its braze-on mount.
  • I also turned the small chainring around so that the numbers imprinted are facing the outside.
  • I'm sure it's not about friction in the cables. Shifting works fine in both direction if the L-screw is further in.
  • The manual mentions that the little pin around which the gear cable is lead can be rotated by 180°. I've tried both positions, the left one improves the issue slightly.

Bike is a Cannondale Synapse Women's (Cann-S2), 9-Speed R3000 Shimano Sora, front derailleur: braze-on type.

The green line is the gear cable.

Image of the derailleur, gear cable and suggested pull direction Image of bottom of frame, non-moveable cable guide afaik

  • Mm good question. Does the cable run under the bottom bracket through an external guide? I wonder if with a different guide it could be further to the left from the point it turns upwards – Swifty May 11 at 21:03
  • 1
    Thanks, I've added an image of that area. Because of the narrow section where the cable runs through I don't think a different guide would be able to improve the angle. – nitzel May 11 at 21:19
2

Having looked through the manual it seems that your shifter cable emerges from the frame on the right hand side of the bike, so the converter should be installed with the pin to the left, which should result in an acceptable angle between the shifter cable and derailleur lever.

I'd definitely rule out all other possibilities that might result in excessive effort required at the shift lever. Detach the cable from the derailleur, put some tension on it (may need to grip it with pliers), actuate the shifter and make sure the cable runs freely. Check the cable run from the shifter to the derailleur make sure there are no snags, housing is properly inserted into stops on the frame etc. You may even want to remove the cable and clean and lube it.

I'd also check the derailleur adjustment. especially alignment. You say the chain rubs at the back end of the cage - if the back end of the derailleur cage is toed out sightly it may be causing the rub. Park Tool has a great step-step video on front derailleur adjustment that can be found here: https://www.parktool.com/blog/repair-help/front-derailleur-adjustment

  • 1
    Thanks for bringing me back to the alignment. I've found reference to a hidden "Support bolt" in the manual on page 11. I'll see if poking that helps and will update here accordingly. Also thanks for editing/cleaning up my question. – nitzel May 11 at 21:27
  • 1
    That bolt C on page 11 fixed the alignment! Then I could tighten the L-screw again and now it's much easier to shift into the big ring. – nitzel May 11 at 21:44
  • @nitzel excellent, glad to help – Argenti Apparatus May 11 at 22:07
  • 1
    @nitzel BTW, you edit would be better suited to an addition to your question rather than in my answer. You can even actually answer your own question with the info about the alignment adjustment in the Sora derailleur – Argenti Apparatus May 11 at 22:14
2

The derailleur was slightly misaligned as Argenti Apparatus had suggested.

To reduce the toe out of this particular braze-on derailleur screw out the support bolt (Bolt C on page 11, 2mm allen key) and re-adjust the derailleur on its mount.

Location of the support bolt

I was then able to screw in the L-screw again and thust he cable-pull-angle was improved. Now shifiting to the big chainring is working fine again.

To reproduce you may need to decrease the gear cable tension to allow the derailleur to move away from the chainring towards the frame.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.