Bicycle Mechanics - Repairing cracked rear dropout

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 Wolf, simple crom-moly steel MTB frame.

In what scientists are calling "perfect timing," 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.

http://ipunchyouintheface.com/images/IMG_9558_600x800.JPG (http://ipunchyouintheface.com/images/IMG_9558.JPG)
http://ipunchyouintheface.com/images/IMG_9570_600x800.JPG (http://ipunchyouintheface.com/images/IMG_9570.JPG)

Good luck with this. The best possible solution is to remove the old dropout and put a new one in, and that way you are certain of a reasonably good fix.
The rear drive-side dropout on my touring bike broke right off, but not near the seat-and-chainstays like yours, and I have brazed it back together using a high-nickel, flux-coated rod. I am not the world's greatest welder by any million-mile stretch, but it seemed to work OK.

Yours is somewhat more difficult, I would suggest. I was able to bevel he edges on each of the two pieces to be joined, and of course they were as clean as possible. And because I was joining two pieces, alignment was an issue which I overcame by using a hollow axle and QR with an all-metal acorn nut triangulated with a brace to the seatstay bridge; it worked brilliantly in keeping the dropout aligned.

The bevelling process for you appears to be near impossible. Which brings us back to replacing the drop-out.

Maybe cross-post in the Framebuilding forum where the real experts on this type of thing hang out.

Hey not a bad idea, I hadn't thought about replacing the dropout entirely. I'll zip on over to framebuilders to see what they have to say. It would certainly be basically as strong as new if I did that I wonder if I can find one locally?

Since it's not a valuable frame, I'd simply TIG weld the forged dropout back together instead of the cost of a new dropout.

Simply brazing the broken ends together won't be strong enough. Brazed joints are used with reinforcing lugs or fillet brazing where there is a lot more joining area. Replacing the entire dropout is the safest route.

I had a break in my dropout very similar to this. I took it to welder who ARC WELDED it for $10. I would not use a torch on it as welding temperatures will melt the solder holding the dropout in the frame and possibly cause the entire dropout to come out of the frame.

Good luck with this. The best possible solution is to remove the old dropout and put a new one in, and that way you are certain of a reasonably good fix.

Shy of that, just clean the paint off that area, align the two ends and run a big ol' bead of brass around that spot. Think Tom Ritchey filet brasing and go for it! I bet it lasts a year or more.

OK, so I'm returning to this after a hiatus with a question.

I have removed the old dropouts from the stays, and I have replacement dropouts in my possession. I have some brazing experience, but this is my first re-braze. There's quite a bit of filer alloy still in and around the slots on the stays. I'm going to try to clean it up as best I can with some teeny files and sandpaper, but I'm wondering how important it is to clear out a lot of the old filler metal. I assume that unless I get amost all of it out of the slots (with a lot of work), it will interfere with the capillary draw on the new filler. Also, I'm going to use appropriate flux and filler for 4130, but is there a problem if it is a different alloy than what is in there now? (like silver vs. brass alloys).

Hopefully I'll be able to get this done Friday and Saturday. I miss riding my bike!

Thanks again to all who helped before, I didn't get much response from the framebuilder's forum.

Finally done with the bike and it's riding great! I had some problems with the right seat stay, it had a small crack at the end, I think from the miles I put on it before I realized it was broken. It didn't help that the ends were put together sloppily in the first place, as I found when removing the dropouts. The left dropout was under tension, so that when I cut it with a chop saw before removal, it separated several millimeters. For the right dropout, they had slotted the stays off-center to get the right alignment. So, the right seat stay only had a tiny bit of material on the outer portion of the slot, and that's where it was cracking (I mean aside from the original cracked dropout).

So here's the final results (click for huge versions):

http://ipunchyouintheface.com/images/bike/bianchi_612x408.jpg (http://ipunchyouintheface.com/images/bike/bianchi.jpg)

http://ipunchyouintheface.com/images/bike/bianchi2_612x408.jpg (http://ipunchyouintheface.com/images/bike/bianchi2.jpg)

Great job!

I've got this frame in the shop if you want to replace it.............

What frame would that be? :)

Looks like an excellent repair. It's always good to see a bike come back to life like this.

I got a warranty replacement frame once when I broke my dropout as you did. Unfortunately, it was a later year model and came with U-brakes mounted on the chainstays.:rolleyes:

What frame would that be? :) I've got a Bianchi Timber Wolf in line for rehab/part out etc.......

Nice job on the repair!

Well done. Also an update on my own job. I left my Fuji Touring unridden for several months because I just wasn't confident about it. Then I had no option when I stripped the hub on the fixed gear I had intended to use for a tour with my girlfriend. The Fuji had to do the job. Well... it worked all the way over 600km! It now needs a bit of a clean-up and repaint (and I might just do a finishing fill of braze before that).

So, I know the satisfaction you are feeling about the repair job -- and also now you know how frame builders can hide myriad sins!