My braze-on type front derailleur (SRAM Force) isn't matching the curve of the big chain ring (50T) very well. It's probably the main cause of the chain jumping off the big ring when I shift up on front from low on the cassette, something I want to fix asap. The high/outer screw is already right on the edge where any lower and it won't shift up in any gear.
Any suggestions on ways to change the angle of the front mech? It's a single bolt braze on; maybe a shim at the top of the back, and the bottom of the front, to maintain some sort of clamping angle. Sounds fiddly. Grinding down the internal face and the external curved washer would be more secure but is obviously a one-way modification.
Maybe it's the angle of the head tube? This frame originally had a standard crankset so maybe the braze-on is angled for a larger 53 tooth chain ring. Come to think of it, the braze-on mount is bolted to the frame, shimming that might be a better option. I could also bend the mounting tab in a vice, but I don't suppose I can find a replacement anywhere.
Maybe I should just convert/upgrade to a yaw-type front derailleur?
trek 5200 front derailleur mount tab.jpg