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  1. #1
    Just keep pedalling! big_heineken's Avatar
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    Rebrazing the Downtube to BB

    The other day I was riding my 87/88 Schwinn Circuit, that has been fully chromed, and the downtube came loose from the bottom bracket lug. The lug also has a crack around the cutout. I took it to a local framebuilder and he told me he could fix it by filing the lug and replacing the whole downtube. I understand that this is a costly and involved procedure.

    Why can't the the lug be filed and the downtube just be re-brazed? Will there not be enough penetration? Would the joint not be strong enough? I'm just having trouble understanding why the bike has to be disassembled to re-braze the lug.



    Hook 'em Horns!

  2. #2
    Old fart JohnDThompson's Avatar
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    It's difficult to tell from your pictures, but at a minimum you'd need to replace the BB shell. If the down tube is cracked as well, that would also need to be replaced. Of course, this would ruin the chrome finish and the cost would approach or possibly exceed that of a replacement frame. Unless the bike has sentimental value to you (or you can do the work yourself), I'd just replace the frame. It's possible that hydrogen embrittlement from the chroming process led to this failure, and if so further failures may occur down the road.

  3. #3
    Senior Member DannoXYZ's Avatar
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    Yes, very possible the acids used in chrome-plating may have damaged the lug & tubing. The other thing is stress-risers caused by the difference in thickness of the joint where the thin tubing goes into a thick lug. What is often done here is to taper the lugs so they get thinner at the ends where they meet the tubing.

    I also see rust at the chainstay-bridge and near the crack. It could be the frame is corroded on the inside and severely weakened. In which case, it's pointless to try and fix just this one crack as others will most likely develop elsewhere.

  4. #4
    THE Materials Oracle Falanx's Avatar
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    Quote Originally Posted by JohnDThompson View Post
    It's possible that hydrogen embrittlement from the chroming process led to this failure, and if so further failures may occur down the road.
    Hydrogen embrittlement doesn't affect copper-based alloys and its the brazing that's failed, and it tends to happen a lot quicker than over a twenty year period... The acid chroming process tends not to leave acid in the component chromed though, because there's a multi-stage rinse and wash after the process by law to prevent hexavalent chromium from exiting the plant.

    Everything else aside, I'd nod in both your directions, twenty years is a long life for a frame with the onset of general corrosion evident, to have put in. Now, it's very likely that the rust is by far worst at the exposed and drilled parts, much like the chainstay bridge, but the only way you'll ever know how much material has been damaged is by removing the rust inside and out. While removal can be as cheap as 20 dollars/quid from a cattle feed merchant for the chemicals, you'll still need an electronic thickness tool to determine the sound metal left...

    The question is, do you really want to keep her?
    "While my father fought for you, I learnt. While my father glorified your petty administration, I learnt. While he longed every day for our line, Adunís line, to be restored, I learnt. He sent me away to bring the Dark Templar back when the time was right!
    "And you tell me that I cannot do this? That I cannot feel the weight of the universe?
    "Damn you, Tellan! Aldaris killed my father!"

  5. #5
    Just keep pedalling! big_heineken's Avatar
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    Thanks for the responses. Those pictures were from when I first got the bike. That is not actually rust, it is grime that looks like rust in the picture. I don't think the BB lug would have to be replaced because the only crack is on the part around the cutout. That part of the lug can be filed off.

    What I'm asking is, why can't it just be rebrazed where it is, without disassembling the frame?
    Hook 'em Horns!

  6. #6
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    Quote Originally Posted by big_heineken View Post
    Thanks for the responses. Those pictures were from when I first got the bike. That is not actually rust, it is grime that looks like rust in the picture. I don't think the BB lug would have to be replaced because the only crack is on the part around the cutout. That part of the lug can be filed off.

    What I'm asking is, why can't it just be rebrazed where it is, without disassembling the frame?
    Because a joint has to thoroughly cleaned before its brazed and this one is old and dirty...just like my creepy neighbor.

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    It looks to me that there wasn't enough penetration in the dt/bb joint and it just cracked/pulled out. I doubt that the chrome had anything to do with it, although I think Falanx has mis-diagnosed to some degree. Some small amount of brazing material did fail in fatigue, but so did the steel bb.

    To answer the question the OP has posed twice, there is no possible way to clean up the bb/dt enough to get penetration. Not cleaning enough has bitten more than one framebuilder. Assuming I am correct, there may have been some reason other than ineptitude that there wasn't enough penetration in the first place. Although ineptitude is a good guess.

  8. #8
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    I don't like brazing on plated metals. But I guess it isn't going to be my problem.

    Not only is it likely dirty, but it is difficult to get a good layer of flux in there. Plus there is some kind of braze in there and I don't know if one has to worry about how it will play with whatever we might try to draw in there. The main thing from a builder's perspective would be that if you can't get it rebrazed to original specs then you are taking on responsibility for a job that is a "maybe".

  9. #9
    Randomhead
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    if the OP finds someone to braze it together, it's not a "maybe" it's a case of being able to find a person that doesn't know what they are doing pretending that they do. You can probably clean it up enough to get 1/16" of penetration, which will last a couple months at most. And my understanding is that the chrome will have to come off or the person doing the brazing will be compromising their health

  10. #10
    THE Materials Oracle Falanx's Avatar
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    Quote Originally Posted by unterhausen View Post
    It looks to me that there wasn't enough penetration in the dt/bb joint and it just cracked/pulled out. I doubt that the chrome had anything to do with it, although I think Falanx has mis-diagnosed to some degree. Some small amount of brazing material did fail in fatigue, but so did the steel bb.
    I dind't diagnose it at all, chap. I just told you what it *wasn't* ;-p I think we'd all agree that if the tube has pulled out, as it were, then whether or not some of the shell has falied is moot. The braze has died a death, otherwise the whole shell must have failed.

    Brazing is immensely strong, but only so far as plastic contraint prevents it from deforming easily. If you've got too much gap, there's plenty of room for plastic work and all the concomittant nasty little mechanical failure processes to have fun.


    Quote Originally Posted by Peterpan1 View Post
    I don't like brazing on plated metals. But I guess it isn't going to be my problem.
    Me either. Although chromium, nickel and copper alloys are all mutually compatible in the liquid and solid phases...
    Last edited by Falanx; 11-18-10 at 05:47 AM.
    "While my father fought for you, I learnt. While my father glorified your petty administration, I learnt. While he longed every day for our line, Adunís line, to be restored, I learnt. He sent me away to bring the Dark Templar back when the time was right!
    "And you tell me that I cannot do this? That I cannot feel the weight of the universe?
    "Damn you, Tellan! Aldaris killed my father!"

  11. #11
    Just keep pedalling! big_heineken's Avatar
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    Thanks everyone. I now understand why the frame will have to be disassembled and the downtube replaced. I was just having trouble comprehending why it isn't as simple a job as it appears to be from the untrained eye.

    Now, the search continues for a new frame.
    Hook 'em Horns!

  12. #12
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by Falanx View Post
    Hydrogen embrittlement doesn't affect copper-based alloys and its the brazing that's failed,
    I can't tell from the OP's pictures what had failed -- shell, tube, or braze. You must have better eyes.

  13. #13
    Just keep pedalling! big_heineken's Avatar
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    Quote Originally Posted by JohnDThompson View Post
    I can't tell from the OP's pictures what had failed -- shell, tube, or braze. You must have better eyes.
    I'm pretty sure it is the braze that failed. The part of the BB lug that cracked, is the small section on the outside of the cutout, where the arrow is pointing.
    Hook 'em Horns!

  14. #14
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    I know that chrome bikes are mighty pretty, but it might be time to retire this one. Even if it were possible to replace or re-braze the BB shell relatively easily, it wouldn't be chromed anymore afterward, and it would need to be re-chromed or something anyway. Probably looking at multiple hundreds of dollars to do it right.

    So, how about finding another Schwinn Circuit or Tempo or Peloton frame of similar age, and having a powder coater strip it and cover it with that new chrome-like powder coat? It looks as nice as chrome and it's much more environmentally friendly. You'd get the same ride quality and nearly the same appearance for less money than it takes to fix the original bike.

  15. #15
    Just keep pedalling! big_heineken's Avatar
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    I've been looking for a similar frame to transfer everything over to, or even a complete bike. I actually bought a 1987 Schwinn Tempo, which would be perfect if it wasn't 1 size up. It rides OK, but it's more like a Cadillac than the Circuit.
    Hook 'em Horns!

  16. #16
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by Falanx View Post
    Hydrogen embrittlement doesn't affect copper-based alloys and its the brazing that's failed, and it tends to happen a lot quicker than over a twenty year period... The acid chroming process tends not to leave acid in the component chromed though, because there's a multi-stage rinse and wash after the process by law to prevent hexavalent chromium from exiting the plant.
    And everyone drives the speed-limit, all auto-repair shops are trustworthy and fixes things the 1st time, all software is written perfectly according to best-practices guidelines and Windows never crashes.

  17. #17
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by DannoXYZ View Post
    Originally Posted by Falanx
    Hydrogen embrittlement doesn't affect copper-based alloys and its the brazing that's failed, and it tends to happen a lot quicker than over a twenty year period... The acid chroming process tends not to leave acid in the component chromed though, because there's a multi-stage rinse and wash after the process by law to prevent hexavalent chromium from exiting the plant.


    And everyone drives the speed-limit, all auto-repair shops are trustworthy and fixes things the 1st time, all software is written perfectly according to best-practices guidelines and Windows never crashes.
    And the OP's frame looks old enough that it might pre-date the multi-stage rinse requirements.

  18. #18
    THE Materials Oracle Falanx's Avatar
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    Quote Originally Posted by DannoXYZ View Post
    And everyone drives the speed-limit, all auto-repair shops are trustworthy and fixes things the 1st time, all software is written perfectly according to best-practices guidelines and Windows never crashes.
    Are we attempting to invoke a Godwin here or such?
    Which statement did you have a concern with? The hydrogen embrittlement one, or the huge EPA fines if you're found polluting with hex chrome? I shall refer you to Ms E Brockovich and P, G & E.

    If you're suggesting a name like Schwinn would be sending frames off to some dodgy, backwater chrome platers...?


    Quote Originally Posted by JohnDThompson View Post
    And the OP's frame looks old enough that it might pre-date the multi-stage rinse requirements.
    It's an 87/88, he said, right? NIOSH dictated the dangers of chromium (vi) in 1975 with strict guidelines for use and made the treatment of it a notifiable, restricted release carcinogen in 1988. The multi-stage rinse requirements were originally a technical measure anyways to give a good plate - don't wash the chemicals off and the plate ends up fuzzy and over-deposited. Putting down bright hard chrome is not an easy process anyways. It's the one finish platers don't offer if they really can't do it, gold for example, by contrast is embarrassingly easy. So compnaies were giving chrome plate the multirinse long before the multirinse and reducing bath were required by law.
    "While my father fought for you, I learnt. While my father glorified your petty administration, I learnt. While he longed every day for our line, Adunís line, to be restored, I learnt. He sent me away to bring the Dark Templar back when the time was right!
    "And you tell me that I cannot do this? That I cannot feel the weight of the universe?
    "Damn you, Tellan! Aldaris killed my father!"

  19. #19
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    I'd just get a new frame. Here's my quick, frank thoughts on the matter. (Not trying to be a jerk!) Fixing a chromed part is a pain in the ass (chrome removal is really annoying, and you NEED to have the chrome removed around that area, lest you risk the health of the welder/brazer during repair), replacing a down tube is a pain in the ass, the repair will cost at least half as much as a new frame, you'd have to get it rechromed afterwards ($$) and why not treat yourself to a new frame?

    Just my 2 cents!

  20. #20
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    Quote Originally Posted by Falanx View Post
    If you're suggesting a name like Schwinn would be sending frames off to some dodgy, backwater chrome platers...?
    I'm sure this bike was not made in the U.S., so who knows how dodgy the plating was? I always envied the Italian builders because they could get their bikes chrome plated without as much fuss and bother as we could. Not sure at what time their environmental laws caught up to ours, I remember trying to get a frame chrome plated in the early '80s, and the good old boy I talked to obviously knew a lot more about the EPA than his lack of teeth would have suggested.

  21. #21
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by big_heineken View Post
    I'm pretty sure it is the braze that failed. The part of the BB lug that cracked, is the small section on the outside of the cutout, where the arrow is pointing.
    Could you take a look inside the BB for me? I'm interested in where the tubing actually ends inside the lug. My suspicion is that the downtube is too short and doesn't fit into the lug all the way down to the BB.

  22. #22
    Just keep pedalling! big_heineken's Avatar
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    Danno, the downtube goes all the way in. The tube is rounded(mitered?) to conform with the shell. I'll try to take some pics tomorrow.
    Hook 'em Horns!

  23. #23
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    Hijack Comments

    Quote Originally Posted by big_heineken View Post
    ... I actually bought a 1987 Schwinn Tempo, which would be perfect if it wasn't 1 size up. It rides OK, but it's more like a Cadillac than the Circuit.
    There's nothing "laid back" about the Circuit.

    Quote Originally Posted by unterhausen View Post
    I'm sure this bike was not made in the U.S...
    Made in Mississippi.

    Quote Originally Posted by big_heineken View Post
    Danno, the downtube goes all the way in. The tube is rounded(mitered?) to conform with the shell...
    I had mine looked over by a vintage specialist who once worked at Romic; he expressed praise for the way the down-tube extended into the shell providing support. BTW, the tubing used in the Circuit passed through his hands before Schwinn manufactured the frame.

    Whether or not this applies to the Circuit model, I viewed the Greenville plant closing video and observed bottom brackets with harp section in place being heated over a large open flame burner. I think that process is what's called "oven braising".

  24. #24
    Just keep pedalling! big_heineken's Avatar
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    Quote Originally Posted by Werkin View Post
    There's nothing "laid back" about the Circuit.



    Made in Mississippi.


    I had mine looked over by a vintage specialist who once worked at Romic; he expressed praise for the way the down-tube extended into the shell providing support. BTW, the tubing used in the Circuit passed through his hands before Schwinn manufactured the frame.

    Whether or not this applies to the Circuit model, I viewed the Greenville plant closing video and observed bottom brackets with harp section in place being heated over a large open flame burner. I think that process is what's called "oven braising".
    I didn't mean the Circuit was laid back, I meant that the Tempo felt like a Cadillac compared to the "sports car" Circuit. I even used the same saddle and wheels to give an apples-apples comparison.

    I had the frame checked out by Hans Schneider, who also worked at Romic. He would be the one repairing the frame, if it gets repaired.

    Do you have any photos of your Circuit?
    Hook 'em Horns!

  25. #25
    Senior Member Werkin's Avatar
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    Quote Originally Posted by big_heineken View Post
    ...I meant that the Tempo felt like a Cadillac compared to the "sports car" Circuit...Do you have any photos of your Circuit?
    The Circuit is sporty for sure.

    Mine came home from a recent eBay purchase almost completely stock. It had issues I'm still correcting, and climbing was a chore, but it was and is a rocket going downhill. BTW, the frame is perfectly straight, although the rear dropout spacing is less than 126mm.
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