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Discussion Starter · #1 · (Edited)
I have a hairline crack following the contour of the hanger and about twice the length of what is visible on my picture, all on the inside of the dropout.

Carbon frame, aluminum dropouts. My first guess would be that the QR pressure somehow cracked the paint, but I'm not sure.

Also there seems to be a small crack on the hanger.

Is any of this cause for concern?
 

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The "green" crack I'd be concerned about right now. It would suck to have your derailleur snap off and go into the wheel. That crack is where the hanger has the greatest potential for flex, so it does worry me.

I'd order TWO replacement hangers NOW, and install one of them when they arrive. Then I'd remove the black paint from the suspect hanger and see if it's just in the paint or in the material.

I advocate anybody who has a replaceable hanger have on hand a spare, because there are so many variations and shops can't stock all of them. Avoid the potential down time.

As for the "blue" crack; it's harder to tell what that is about.
 

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That color of red is most likely over a base coat of white, basically the most common colors to crack because of how thick they are laid on. Seeing the crack in the paint follow the contour of the hanger doesn't seem all that surprising. Just an opinion from some guy on the internet, but it wouldn't worry me, not with how a pure carbon dropout is constructed.
 

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Discussion Starter · #4 ·
but it wouldn't worry me, not with how a pure carbon dropout is constructed.
It's actually an aluminum dropout bonded to the carbon frame. If it's a solid block of aluminum, I guess it would not be too bad, but I have no way to tell.
 

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Doh, you're right. Hadn't had my coffee yet. Still though, that most likely means it's where the bond joint is and with a heavy paint, cracking is almost inevitable. If it were me, I'd have my shop document it and then just keep an eye on it for changes. Chances are good it'll be fine long term.
 

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Discussion Starter · #6 · (Edited)
The "green" crack I'd be concerned about right now. It would suck to have your derailleur snap off and go into the wheel. That crack is where the hanger has the greatest potential for flex, so it does worry me.

I'd order TWO replacement hangers NOW, and install one of them when they arrive. Then I'd remove the black paint from the suspect hanger and see if it's just in the paint or in the material.

I advocate anybody who has a replaceable hanger have on hand a spare, because there are so many variations and shops can't stock all of them. Avoid the potential down time.

As for the "blue" crack; it's harder to tell what that is about.
Turns out the hanger is machined like that. got my hands on another one and they all look the same.

The part where the hanger is installed is also a solid block of aluminum (can be seen through the cable holes) . So it's almost certainly just a surface paint crack. All is well.
 
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