Repair options for a cracked rear dropout
05-24-17, 05:29 PM
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I wrote that it was in tension, but of course it's not in tension 100% of the time--the "tension" represents the worst-case scenario which is what it must be designed for. In certain conditions, the reaction from the axle will indeed be pushing towards the front of the dropout or perhaps to the top/front (let's say the 1 o'clock position if the top of the drop was 12:00) . However, the worst-case scenario might be when the frame is flexed, perhaps leaning in a corner, or braking, and in those cases the axle is wanting to "open" the dropout slot. Perhaps hitting a pothole, then the axle is driving upwards into the rounded upper part of the dropout slot. That is also trying to "open" the dropout and thus putting the cracked area in tension. Or hitting a pothole while leaning and braking! A hundred pounds of force, twisting the other end of the axle, can act like a lever and try to force that slot open with tremendous force.
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05-24-17, 05:50 PM
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I had a cracked DO repaired by a frame-builder but the V-cut-groove and tig-weld-up approach was what he used and though it was "lumpy" when completed after some shaping and filing and touch-up it was OK looking. AND it never broke again! Lost the adjuster hole but small price to pay for a STRONGER D/O.
05-24-17, 08:47 PM
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My list of options- If the OEM drop out can be sourced then replace it. Chrome will be ruined but can be redone is the $ are there. Could be that the chrome aided the crack, Hydrogen embrittlement and all.
If the OEM drop out isn't available then weld away with a good welder how has done this before. Getting a clean adjusted screw hole and chrome removal first, IMO, is very important for the best result.
Last choice would be to fill the screw hole with brass. Again clean is best. Andy
If the OEM drop out isn't available then weld away with a good welder how has done this before. Getting a clean adjusted screw hole and chrome removal first, IMO, is very important for the best result.
Last choice would be to fill the screw hole with brass. Again clean is best. Andy
05-24-17, 10:14 PM
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TIG with stainless rod. The difference in color between the weld and the chrome will be quite small.
I can recommend a frame builder here on the west coast who has done these repairs before but I bet a few phone calls will land you someone closer who can weld this.
Brent
05-24-17, 10:58 PM
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My list of options- If the OEM drop out can be sourced then replace it. Chrome will be ruined but can be redone is the $ are there. Could be that the chrome aided the crack, Hydrogen embrittlement and all.
If the OEM drop out isn't available then weld away with a good welder how has done this before. Getting a clean adjusted screw hole and chrome removal first, IMO, is very important for the best result.
Last choice would be to fill the screw hole with brass. Again clean is best. Andy
If the OEM drop out isn't available then weld away with a good welder how has done this before. Getting a clean adjusted screw hole and chrome removal first, IMO, is very important for the best result.
Last choice would be to fill the screw hole with brass. Again clean is best. Andy
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05-24-17, 11:24 PM
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Sure, but a well nailed construction beats a poorly bolted one. 
Andy
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05-24-17, 11:45 PM
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Notes seem to indicate that 309 rod might work, but you're probably just as well off to weld with regular carbon steel rod, and paint.
Even if you just paint the dropout, you'll have the right part in it, and it could be chromed later.
05-25-17, 12:25 AM
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+1 on welding...Chamfer both pieces on all sides so you have V (valley) for a good strong weld. You can then later file the excess from the drop and still have enough strength in the weld that it will not cause any additional worry.
Bring it to a pro to do the welding. Use a heat sink at the tubes to minimize heat to chrome and paint and you will be good to go....no gas (Oxy-ace) welding, let electricity and wire be your friend. Easy and quick job.
Ben
Bring it to a pro to do the welding. Use a heat sink at the tubes to minimize heat to chrome and paint and you will be good to go....no gas (Oxy-ace) welding, let electricity and wire be your friend. Easy and quick job.
Ben
Might want to use a short bolt w/ nut and washers at the open end of the DO to keep the ends aligned during welding.
05-25-17, 12:52 AM
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Thanks for all the thoughtful responses - interesting discussion. I'm going to mull it over, maybe release it to the masses.
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05-25-17, 06:37 AM
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Didn't Trek use similar rear dropouts on their bikes?
05-25-17, 06:45 AM
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John, I was going to post and ask you, what's your opinion on TIG'ing vs filling the adjuster hole with brass, or even silver, and getting it to flow through the crack via capillary action, then file and sand?
I'm pretty convinced it could be done without ruining the chrome up on the stays, and since the dropouts are painted, that could be easily touched up.
I'm pretty convinced it could be done without ruining the chrome up on the stays, and since the dropouts are painted, that could be easily touched up.
05-25-17, 06:54 AM
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05-25-17, 07:12 AM
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The chrome on the dropout cannot be saved. But as several people have said, if welding heat is sufficiently isolated, it need not destroy the chrome on the stays. If you destroy the chrome on the stays, you will have to rechrome the stays and repaint the whole frame, an expensive repair, after which any scoffer can rightly say "it's a repaint!."
An otherwise original finish frame with only a competently welded dropout, it seems to me, is preferable to that.
If you really want to preserve the look of the chrome on the dropout, after the welding and filing you could cut a thin stainless steel C and silver solder that to the face of the dropout. You could even stamp GIPIEMME on the stainless C, but I don't think it's worth that effort.
An otherwise original finish frame with only a competently welded dropout, it seems to me, is preferable to that.
If you really want to preserve the look of the chrome on the dropout, after the welding and filing you could cut a thin stainless steel C and silver solder that to the face of the dropout. You could even stamp GIPIEMME on the stainless C, but I don't think it's worth that effort.
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05-25-17, 07:21 AM
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Such a pretty frame. Shame about the crack. If it gets you a good price with the repair, well, once you clamp a wheel in there, no one will see it while you ride.
05-25-17, 08:22 AM
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The problem would be getting the interior of the crack completely clean. This would be an issue whether the repair was brazed or welded. The best way to get it clean, as suggested above, is to grind out a V-shaped channel where the crack extends. This, of course, would damage the chrome. I would forgo trying to preserve the chrome and then fill the adjuster hole to prevent it from being a stress raiser again after the repair.
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05-25-17, 09:08 AM
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I just went through this with a Montello, the brazing burned the chrome up the seat and chain stays about one and a half inches beyond the dropout. Rather then deal with trying to get a good chrome job (which is an issue in Tucson) I am considering having the bottom of the two rear triangles painted to cover the dropout and burned chrome.
05-25-17, 09:49 AM
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A half centimeter of adjustment in the effective chain stay length might be enough to make a difference in tuning the setup for the demands of a particular race or tire width. With the hub closer to the BB, the BB would also be slightly higher - for crit racing?
I was thinking about this the other day while looking at a frame with similar dropouts.
It may also be designed to enable running FG for old school winter training.
I was thinking about this the other day while looking at a frame with similar dropouts.
It may also be designed to enable running FG for old school winter training.
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05-25-17, 10:08 AM
#43
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I recognize this scenario (Only seen this once.):
Frame was dropped bare onto a concrete floor, it was caught but landed on the derailleur hanger. This pinched the dropout so that the wheel axle could not slide in. The customer used a bar to spread the dropout back. The dropout cracked at the adjustment screw hole (stress riser). The customer found a frame builder to replace the dropout.
Frame was dropped bare onto a concrete floor, it was caught but landed on the derailleur hanger. This pinched the dropout so that the wheel axle could not slide in. The customer used a bar to spread the dropout back. The dropout cracked at the adjustment screw hole (stress riser). The customer found a frame builder to replace the dropout.
05-25-17, 11:06 AM
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Well I gave it some thought and it really is too small for me, if only a cm bigger .... Plus I'm closing a deal on a De Rosa today!
. . : : G V H : : B I K E S : : . .
GVH bikes is having a moving sale. Click on the frames link. There are some decent deals on some other nice frames and parts, but no screamers like the Cinelli. Someone really should get it!
. . : : G V H : : B I K E S : : . .
GVH bikes is having a moving sale. Click on the frames link. There are some decent deals on some other nice frames and parts, but no screamers like the Cinelli. Someone really should get it!
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05-25-17, 12:20 PM
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