Originally Posted by
Doug Fattic
Braze-on front derailleurs vary a lot in where the attaching bolt is in height above the bottom bracket. This is one reason I gave up using front derailleur braze-ons (as well as the reason JDT mentioned already). I remember a new model of a Dura Ace front derailleur needed to be 4 mm higher than the last model. So one answer is to look for a different model front derailleur. As a frame builder I would look closely at the boss and perhaps take a file to the slot to make it a bit longer going higher (and perhaps it needs to be widened too?).
Actually if it was on my workstand I would look at the backside of the braze on mount, to review the uniformity of that trough.
Note First generation Campagnolo Corsa Record front mechanisms had their point point at the near Bottom of the body!?! That would be one way to solve the problem.
Campagnolo soon enough modified that. But they are out there.
timeline note, investment cast braze on mount parts were a mid 80's thing.
early 80's and it was stamped steel, also pre SLX and lots of flex, never liked them as a mechanic.