Sora triple derailleur not working on 39-50 double. Why?

[Ugo51]

Hi all,

I just finished up building a bike, and I used a Sora FD-3030 coupled with an old DuraAce crankset, with 39-50 rings. It doesn't work. The derailleur just pushes the chain against the outer chainring and jams it there. I played with height, but I am limited by the fact it's a braze on.
The FD-3030 has a maximum of 50T, a max capacity of 20T and a max jump of 11T, so all should be good, no?
It works well when I installed a different crank with 36-46 chainrings.
Am I missing something?

 

[clubby]

Have you adjusted the mech limit screws? For a 50t ring with a 50t max, the top limit screw will be pretty much all the way out.

 

[Ugo51]

The limits screws are not to blame in this case. They are set correctly, but they only limit (du-uh) the lateral movement of the derailleur cage.
I think I understood the problem now: it's the combo derailleur+chain line.
When shifting, as the derailleur's cage moves outwards, it also raises up. In a triple setup, the outer ring is normally a few mm further out than it is in my current setup, so the cage sits quite low when trying to shift the chain to the 50T ring. Too low, in fact, and it ends up jamming the chain on the chainring instead of shifting.
Sadly, it's a braze on system, so I cannot go any higher than this with the derailleur. Hence, I'll have to buy a new one...

 

[fishyfool]

I ran into something like this if I understand what you're saying correctly.
I set my lower limit screws correctly. Then, grasp the cable and keep it taut while using the arm (cable attachment arm) to set a little preload on the arm so it pushes the cage out a bit, then tighten the screw to set the cable in place. You can play with the preload until it does what you desire.