Lots of fun discussions on long cage derailleurs here lately. I recently came into a first version Campy Rally on a rough Raleigh. I have read how they break and I can see the weak spot. My question is what causes them to break there? Is it from rough use with lots of tension while shifting? Maybe just fatigue and falls apart? Or is it from an added stress like a dropped chain binding everything up and this is the weak spot? I am hoping it is abuse and careful use could increase the odds of it lasting. Thoughts?

Likely all of the above?

I thought it was just from dropping the bike on that side. I mean, if dropping it can easily bend a dropout, it doesn't seem like it would be hard to snap a derailleur with a weak spot right there.

Huh good question. I've seen a half dozen or so that broke and maybe another half dozen in pictures, but I was never there to witness it. I just assumed it was from the bike falling over/crashing, or maybe shifting past the big sprocket into the spokes. But even going into spokes is so often a secondary effect of the bike falling or crashing, and bending the hanger in enough to let it hit the spokes. So I'm putting my money on the broken ones were in contact with the ground at least once.

I'd be surprised if any broke just from normal use, like during a normal shift, or JRA.

I wouldn't expect one to break JRA, though I've seen newer 8/9s Record models split their B-knuckle surrounding the bushing from what seemed like excessive press-fit force.

Thanks for the replies and that sounds encouraging. I kinda thought maybe a chain getting tangled up might be the greatest risk as the weakest link in the system would give first. It would be a shame not to use it as they are a thing of beauty. That being said, it seems they are fairly valuable on the used market so I wouldn’t want to destroy it either. I do ride gently and fairly sedately, so ride on. This very well used Raleigh came with a first generation Dura Ace crankset too, so that will be put back on. It won’t wind up as a stock bike, but the fancy parts will look better than the rough frame cosmetic condition.