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Old 11-05-08, 08:22 PM   #1
Tunnelrat81
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Crack in steel dropout...What to do?

So the other day I picked up a new chain to replace the older, abused one on my commuter bike, a mid-80's Univega Gran Premio with Shimano 600 SIS drivetrain and D/T shifters. Ever since installing it I've had a problem with phantom shifting. I'm fairly good at tuning a R/D and fidgeted back and forth wondering why it was being so stubborn before finally putting it on the stand tonight and doing some work.

After replacing the small piece of cable housing with a spare piece of new stuff I had, I again checked my "master pin" for tightness and went on to check the hangers alignment. I pulled the wheel off and removed the R/D and immediately noticed a big crack just in front of the dropout. I immediately was both grateful and disappointed at the same time. "Thank goodness I had the R/D problems before this thing broke off" as well as "How am I going to fix this thing?"

So I'm posting some pictures for you guys to get an idea of a safe way of addressing this. I work fairly close to a great machinist and if it's safe to weld I'd trust that he'd do as good a job as any, but I'd like to know if there are any other options short of throwing the frame away. This bike belonged to my late uncle who died years ago from cancer and it's become my main mode of transportation to work and back. I've upgraded it along the way and one of the few remaining pieces is the frame. So it does carry some sentimental value.

Thanks,

-Jeremy


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Old 11-05-08, 08:28 PM   #2
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That should be repairable. Make sure everything is well aligned before doing the job. It looks like it started quite a while ago.
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Old 11-05-08, 08:28 PM   #3
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Any frame builder could either braze the crack to repair it or even replace the entire dropout.
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Old 11-05-08, 08:53 PM   #4
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That should be repairable. Make sure everything is well aligned before doing the job. It looks like it started quite a while ago.
I thought about that, and there's no way to really know how long it's been like this. Do you think it's probable that the phantom shifting was due to flexing at the dropout? It's pretty scary to think about this since I don't just ride this back and forth to work, it's my loaner/backup bike for weekend rides as well. I'll most likely talk to the guy at work tomorrow and see if he's willing to fix it up for me.

-Jeremy
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Old 11-05-08, 09:04 PM   #5
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+1 Looks old, due to discoloration of metal inside crack area. Fresh crack would have bright metal showing.

+1 Find someone good to weld it/braze it. Or better yet, perhaps a new drop out.
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Old 11-06-08, 04:28 AM   #6
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I'd have no qualms at all about welding that. Grind the crack open until it looks like an hourglass when seen from the top/bottom of the bike, then weld it back in. Arc being preferred over oxyacetylene, even stick would do. If you'd like a belt-and-suspenders approach you could cut a patch that'd fit inside the cutout in the dropout and weld that plug into place as well for some extra reinforcement.
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Old 11-06-08, 08:53 AM   #7
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The only problem I could see with welding is the possible loosening of the brazed joints at the stays. If done carefully I would think it would be perfectly safe. As in striking an arc, welding a tiny bit, then stop and let it cool completely before the next weld. Use an old threaded axle to hold it in place, even thick metal has a tendency to warp when heated up. I'd cut out the crack as stated earlier in an hourglass, but from side to side rather than vertical. When standing at the back of the frame looking down it would look like this >< Three or so small welds on the face and inside the drop should fill it in. Brazing would work too of course, but in a high stress area like this I'm not sure about the longevity of the repair. I could be wrong, though.,,,,BD
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Old 11-06-08, 09:19 AM   #8
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The only problem I could see with welding is the possible loosening of the brazed joints at the stays. If done carefully I would think it would be perfectly safe. As in striking an arc, welding a tiny bit, then stop and let it cool completely before the next weld.
A half-inch weld like that is the work of seconds. I'd worry more about stop-and-go welding adding impurities to the seam than about heat build up upsetting the brazing.

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I'd cut out the crack as stated earlier in an hourglass, but from side to side rather than vertical. When standing at the back of the frame looking down it would look like this ><
... An hourglass when seen from the top or bottom of the bike, we're saying the same thing.
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Old 11-06-08, 09:26 AM   #9
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I'd have no qualms at all about welding that. Grind the crack open until it looks like an hourglass when seen from the top/bottom of the bike, then weld it back in. Arc being preferred over oxyacetylene, even stick would do. If you'd like a belt-and-suspenders approach you could cut a patch that'd fit inside the cutout in the dropout and weld that plug into place as well for some extra reinforcement.
^
+1

I had a similar crack on one of my dropouts, and Paul Sadoff (Rock Lobster) ground a "V" on both sides ("hourglass"), repaired it on both sides (unsure whether he welded or brazed it), and finished it with a grinder. It has held up well.



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Old 11-06-08, 09:48 AM   #10
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Originally Posted by Scooper;7801498I
had a similar crack on one of my dropouts, and Paul Sadoff (Rock Lobster) ground a "V" on both sides ("hourglass"), repaired it on both sides (unsure whether he welded or brazed it), and finished it with a grinder.
Looks like there's a yellowish tinge to the exposed area in the top pic. That'd be the actual material added during brazing shining through. In that case better to stay with brazing, as welds gets really unhappy when you try to join too dissimilar metals.
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Old 11-06-08, 01:15 PM   #11
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I've brazed quite a few of those back. Although in about 1/2 the cases, it was actually separating at the original brazed joint itself.

In this case, there's so much rust and corrosion that cleaning the joint would be difficult. Brazing only works well if you have sufficient surface-contact area and minimal gap between the mating surfaces. Personally, I would grind a V-notch on both sides and TIG weld that back together. You can attach some heatsink clamps between the joint and the end of the chainstay to suck heat away to not melt the brazed joint.
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Old 11-06-08, 01:32 PM   #12
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A half-inch weld like that is the work of seconds. I'd worry more about stop-and-go welding adding impurities to the seam than about heat build up upsetting the brazing.


... An hourglass when seen from the top or bottom of the bike, we're saying the same thing.
Ahh, thought you meant as seen from the side. Impurities? I was talking less than an hour, not a weld every two weeks.,,,,BD
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Old 11-06-08, 02:25 PM   #13
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Well an update, but no pictures yet. I'm still on my lunch break and just tossed the frame back into my car after the job.

After taking a good look at what he was dealing with, our machinist quickly grinded some deep/narrow grooves exactly like you guys suggested from either side of the crack, leaving only a really thin layer in the middle. Then he grabbed his TIG welder and went to work for about 1-2 min. per side of off and on welding and just like that he was done. The final product looks good and I probably won't even file on it much, if at all.

I'll have to figure something out for putting at least some primer on the section to protect from corrosion, but as far as matching paint, I don't have the finances or the interest to make a 'proper' cosmetic repair. (that repair pictured above is beautiful) The frame has other surface scratches on it and cosmetic damage, not to mention the fact that it's not a high end frame in the first place. I just need it to be back to the same reliable bike that I've been appreciating over the past two years of commuting on it.

Oh, and he gave it his official "50+ mph" rating when I asked him if he'd trust it under rigorous use.

Thank you all for your help, and for those who are interested, I'll put a picture up for you tonight when I get home. I'm crossing my fingers that this break is what was causing my drivetrain to skip as well. I'll find out tomorrow. =)

-Jeremy
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Old 11-06-08, 02:31 PM   #14
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Also, in the case that the heat was too great for the brazed nearby joints, would there be any indication at all that there was a problem? As my above post mentions, he didn't wait long between welds and it didn't take long after the job was done to be able to touch the part with bare hands.

Would I be able to notice at potentially damaged brazed joint?

-Jeremy
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Old 11-06-08, 02:53 PM   #15
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Also, in the case that the heat was too great for the brazed nearby joints, would there be any indication at all that there was a problem?
If the paint is OK I can't imagine that the brazing would be in any danger.
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Old 11-06-08, 02:56 PM   #16
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Impurities? I was talking less than an hour, not a weld every two weeks.,,,,BD
Well, the welder that I have tends to sputter a little at start and leave a sooty residue afterwards. I definitely get better welds when I can do them in one go.
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Old 11-06-08, 03:45 PM   #17
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Don't braze, don't put a torch on it or the solder will run out and the whole dropout will fall out, most likely. In any event, brazing is not a proper fix for a crack in steel.

I had an almost identical crack. The welder took a thin grinder to the crack and cut all the way through it then ARC WELDED it back together. It is a perfect repair.
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Old 11-06-08, 04:22 PM   #18
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Arc-welding doesn't give as strong a joint as TIG due to the sputter and hydrogen-embrittlement of the joint. Heck, even MIG welding is better than arc. With a skilled hand, you CAN repair it by brazing. Just that filling large-gaps via brazing doesn't give as strong a bond as tight-fitting joints (like lugs into tubing-ends, see before & after picture above). TIG gives the strongest weld on butt-joints with steel.
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Old 11-06-08, 05:07 PM   #19
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Well the paint IS darkened around the dropout from the heat. I assume the joints you're worried about are where the flat steel of the dropout connects to the tube steel of the seat and chain stays correct? We're not talking about a lugged dropout here, but one that's smoothly formed together straight onto the stays. Not being terribly familiar with frame building, I'm not sure if this type of joint is brazed or welded, or what the technical differences are. So someone will have to explain that to me.

As I mentioned above, I plan on posting some 'after' pictures of it tonight when I get home and will more closely inspect everything then to make sure it looks trustworthy.

I've throroughly enjoyed this discussion though, and I do think that it will be perfectly safe for years to come after this repair, but you've given me a lot to think about and check before going forward. For that I thank you. =)

-Jeremy
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Old 11-06-08, 06:38 PM   #20
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That vintage of Univega is brazed. Discoloration of the paint is fine and to be expected. Clean up the repair with a file or dremel. Wire brush the area and rattle-can it with a color you can live with. Your bike now has even more "character".
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Old 11-06-08, 09:32 PM   #21
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Well here is a picture of the repair as it will be until perhaps this weekend when I'll have some time to clean it up and spray with some primer. Looking at the picture I notice that the welded section is a bit narrower than the rest, which I might have said something about when he was doing it, but I'm stuck with now since he didn't charge me a penny for his time. I tried to offer him something and he smiled and said, "you need your bike, so I can't really charge you for it." There's no way I can go back and ask him to improve on his free service.

Anyway I really appreciate your advice and discussion. Please pipe up if you have any comments or concerns about the finished product. I'm planning on riding it to work tomorrow. I've already got the R/D and wheel back on and after a test ride it was confirmed that the skipping gears were a direct result of the flexing dropout, which makes perfect sense. That means it didn't break until mid-ride this last Saturday during a nice easy paced 28 mi. jaunt with some friends. The crack has obviously been in the making for months and possibly longer, but must not have gone all the way through until this Sat. That's when the shifting started misbehaving. I'd associated the problem with the chain since coincidentally I had just swapped it out on Friday.

Again thank you all.

-Jeremy



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Old 11-06-08, 09:53 PM   #22
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Free is an excellent price. You have a very good friend. You will be fine with this repair. Give it a good brushing before painting.
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Old 11-06-08, 10:07 PM   #23
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Looks good enough to me too. Might even be stronger than the original?,,,,BD
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Old 11-06-08, 10:50 PM   #24
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One more question before I let this thread die....

The above picture by scooper shows a break in the exact same spot on the frame, and I'm wondering what it is, if anything more than normal use, that causes the break in this particular spot. Could it have been a previous crash, a hard impact? Or is it just the constant drivetrain forces pulling back and forth on it until it goes?

Its just hard to imagine normal use slowly tearing through a perfectly good dropout. I realize this thing is super old, and amazing things can happen slowly, but if this failure is more common than say the same break on the non-drive side, than it seems that frame builders may sell two versions of the dropout, a normal one and a slightly beefed up version for the driveside. If it's just wear over time, should I be checking this repair weekly just in case?

-Jeremy
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Old 11-06-08, 11:17 PM   #25
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It probably didn't happen slowly, more like a quick pop after years of fatigue. Just lots of miles and flexing from sprinting, rough roads, etc. Normal for a bike that is used regularly over many years. Definitely keep an eye on it, but I wouldn't worry too much.,,,,BD
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