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Old 11-29-07, 01:50 AM   #1
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Join Date: Jun 2006
Location: berkeley, ca
Bikes: 95 Bianchi Timberwolf; 06 Lemond Croix de Fer
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Repairing cracked rear dropout

This is a crosspost from the mechanics forum that might do better here.

I felt some clunking in the drivetrain at the end of my ride today, and when I got home I discovered the drive-side rear dropout had cracked right where it meets the chainstay. This bike is old and not worth much, but it has a lot of sentimental value and I'm strapped for cash; so I'm going to try to repair it myself. The bike is a 95 Bianchi Timber Wold, simple crom-moly steel MTB frame.

Perfect timing though, I have been taking a welding class this quarter at UC Davis and have full access to the shop. I have been practicing brazing with oxy-acetylene, MIG, and arc rod welding, plus they have a TIG available (but I've never used it). So I'm wondering what process I should use to fix this. Is brazing strong enough alone, or should I add a reinforcement strip to the outside? What brazing alloy would be appropriate for 4130? I've read that framebuilders use silver alloys, but want to know if another would work. Or should I use an arc process?

The main thing I care about the repair is strength: I'm 235 lbs, plus this is a utility bike that carries extra weight often. Looks, don't care. I'm going to sand down the dropout and stays near the dropout and rattlecan it black afterward anyways.

Here's some pics.

It was suggested in the mechanics forum that I replace the whole dropout. I like that idea, but then I need to know how to find a good match in a replacement, one that will fit into the slots in the stays and be roughly in the right place across from the other dropout. I'm not against replacing both dropouts with new forged ones so that they match

Thanks in advance!
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