Dura-Ace FD bracket break, repairable ?
 

Dura-Ace FD bracket cracked.
Would this be a candidate weld fix ?
Its in great condition and vintage.
Maybe easier and/or cheaper just to find another ?
If I could weld then I would probably know the answer and do it if possible.
These pix show the break
https://cimg4.ibsrv.net/gimg/bikefor...3be12ba01.jpeg
https://cimg9.ibsrv.net/gimg/bikefor...8553ec7a1.jpeg
https://cimg1.ibsrv.net/gimg/bikefor...ae84f1d7a.jpeg

Do you have any idea what aluminum those are made from? I am somewhat skeptical due to any number of reasons.

Im not really sure but the answer is probably too low of quality AL. Why not use that airplane grade AL that some of the better frames are made out of ? Im thinking Colnago Dream bikes. Ofcourse I did not use a torque wrench but I dont think that I was going too tight, I have hand tightened most all (not CF) over of the decades.

The problem with not knowing what grade aluminum is that it would be a crap shoot finding the right filler.

What Eric said and the anodizing will need removal too. The tiny cross section and minimal clearance with the clamping bolt further make a repair challenging. I suggest finding a replacement der, or a donner one to use the front and hinged part and see if the hinge pin can be removed. I have seen many examples of this type of breakage. I have yet to see a repair that was welded. Andy

getting that pin out is going to be difficult, since it's blind from one side. I'm happy to say I have never done this to a derailleur, although I know it's not uncommon.

Yes I figured this type of weld would be too complicated and better to just find a replacement. Just a shame that the unit is in such nice condition. This is an example of AL fatigue / fracture and why most preferred steel frames.

The failure was not due to fatigue, as far as I can tell. Your pictures aren't great, but fatigue on something like this would show some amount of discoloring on the fracture surface. From what I can see, the fracture surface shows only evidence of rupture, i.e. the bolt was overtightened. Rupture surfaces are rough. Fatigue is smoother.

Most of these break due to careless mechanics at work.

I don't have the equipment to build aluminum frames, and I'm not sure I would do it if I did have the equipment. But on the occasions where I'm buying a bike, I buy aluminum frames if it's an option. Steel is a premium option nowadays, so the less expensive steel frames are more expensive than aluminum frames on what is otherwise the same bike. I prefer to pay less for a lighter aluminum frame.

I've successfully replaced the clamp piece on Huret Jubilee front derailleurs, but the problem I see with this Dura-Ace unit is that the hinge pin appears to be set in a blind hole. That makes extracting the current pin difficult.

I agree that a welded repair is unlikely to be satisfactory.

I am afraid I threw away my Jubilee with a worn out cage. I never realized people broke the clamp so often or I would have tried to fix it. I always thought it as the most elegant FD.

Might be possible to drill out the hinge pin, source a replacement clamp from a worn donor then improvise a new pin?

The aluminum bits on the busted clamp could be ground down with a dremel until you get down the pin, then it could be cut in half and pulled out with vice grips. Something to that effect anyway. No clue where someone would find a suitable replacement clamp though.

Did not know that fatique "would show some amount of discoloring on the fracture surface".
Will surely be more careful now with tightening and max torque.