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Old 06-17-17, 06:45 PM   #1
nesteel 
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Critique, and advice needed

I have a vintage Trek frame that needed the FD cable guide brazed back on. I obtained a correct replacement (original was mangled), flux, and stay silv 56 brazing fill.
Here are a couple pics. I looks like the flux was exhausted where I had the guide clamped to the BB shell.



What is the likelihood that the BB shell got hot enough to soften up the other joints? Or am I just being paranoid?

Here it is cleaned up.




The shorelines look okay, and it appears that the braze flowed through to the backside well. Opinions?

Also, the lower headlug has an open shoreline. Is it possible/recommended to fix that by heating up the joint and flowing more braze into the joint? Should this be done with the frame fixtured up? Or is possible "freehand"?

Thanks for any and all tips/advice.
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Old 06-17-17, 08:47 PM   #2
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brazing looks good. Not sure what your concern is, most people get flux toasty occasionally.

You don't need to fixture a lug to fill a shoreline. Cleaning it well enough to get any penetration might be an issue
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Old 06-17-17, 11:25 PM   #3
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brazing looks good. Not sure what your concern is, most people get flux toasty occasionally.

You don't need to fixture a lug to fill a shoreline. Cleaning it well enough to get any penetration might be an issue
Thank you.

My main concern was how hot you can get the BB shell before it starts to affect the other brazed connections.
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Old 06-18-17, 04:59 AM   #4
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if the filler material at the sockets didn't move, it wasn't affected.
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Old 06-18-17, 10:57 AM   #5
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Just that bending the piece to curve around behind the seat tube

would have been easier , before it is brazed on.
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Old 06-18-17, 11:41 AM   #6
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Just that bending the piece to curve around behind the seat tube would have been easier , before it is brazed on.
It is easy to bend now that it is brazed on. Just tap the back end with a small hammer until it will place the cable right to the front derailleur. These braze-on gear cable guides became unpopular for several reasons. !st they are likely to pull off when brazed with silver (just like this one did) even if brazed correctly. The small point in front can start to fail (because the cable can put quite a stress on its small front point when pulled to change gears) and eventually the break keeps working back. And 2nd it is hard to get paint between the back of the boss. Time has proven they are a poor design.
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Old 06-18-17, 12:11 PM   #7
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It is easy to bend now that it is brazed on. Just tap the back end with a small hammer until it will place the cable right to the front derailleur. These braze-on gear cable guides became unpopular for several reasons. !st they are likely to pull off when brazed with silver (just like this one did) even if brazed correctly. The small point in front can start to fail (because the cable can put quite a stress on its small front point when pulled to change gears) and eventually the break keeps working back. And 2nd it is hard to get paint between the back of the boss. Time has proven they are a poor design.
The original was brazed very poorly. Barely any braze along the two exposed edges, and no braze present at all in the joint space. Not surprising it failed. Considering the frame, I felt it was required to put back an original type cable guide. It will be "tweaked" for proper cable path.
Thanks for the pointers and advice everyone. It is much appreciated.
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Old 06-19-17, 12:38 PM   #8
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I have a vintage Trek frame that needed the FD cable guide brazed back on. I obtained a correct replacement. […] What is the likelihood that the BB shell got hot enough to soften up the other joints? Or am I just being paranoid?
That looks like a 750/950 type frame, in which case the other joints will be done in brass, and you used a low-temperature silver for the cable guide. So, no danger at all of that happening.

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The shorelines look okay, and it appears that the braze flowed through to the backside well. Opinions?
As long as the silver was pulled all the way to the back side of the guide, you should be fine.

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Also, the lower headlug has an open shoreline. Is it possible/recommended to fix that by heating up the joint and flowing more braze into the joint? Should this be done with the frame fixtured up? Or is possible "freehand"?
Freehand, with a low-fuming bronze (assuming I'm right about the frame) ought to be fine. Those frames were originally brazed freehand after being tack-brazed in a fixture.
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Old 06-20-17, 07:31 AM   #9
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I don't think it really needs to be LFB if the OP can clean it out enough to use silver. LFB does seem to be a little more tolerant of crud.

Doug's post is the first I've heard of problems with those cable slings. I can see if there was poor fit that some silver fillers might not have the strength. Otherwise, there is plenty of surface area. I always figured they went away because of paint and because a sling under the BB shell costs a fraction of what a pair of these slings cost.
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Old 06-20-17, 10:15 AM   #10
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I don't think it really needs to be LFB if the OP can clean it out enough to use silver. LFB does seem to be a little more tolerant of crud.
You may be right. Your choice, OP!

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Doug's post is the first I've heard of problems with those cable slings. I can see if there was poor fit that some silver fillers might not have the strength. Otherwise, there is plenty of surface area.
The only failures I've seen are from poor brazing (as in the OP's example) or abuse. I have noticed that Campagnolo's guides seem to be formed from thicker stock than some of the no-name guides, so that may be a factor as well.


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I always figured they went away because of paint and because a sling under the BB shell costs a fraction of what a pair of these slings cost.
Less labor as well. Just drill a hole and pop in the guide.
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Old 06-20-17, 11:24 AM   #11
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You may be right. Your choice, OP!



The only failures I've seen are from poor brazing (as in the OP's example) or abuse. I have noticed that Campagnolo's guides seem to be formed from thicker stock than some of the no-name guides, so that may be a factor as well.




Less labor as well. Just drill a hole and pop in the guide.
Dave, I can pretty much guess this frame was built on a monday. Between the open shoreline, the poor braze job on the cable guide, and the crooked brake bridge......
Sucker still rides so well though.
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Old 06-24-17, 08:21 PM   #12
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well, I'm not Dave and John isn't Dave, but my guess is it was built on Friday after lunch. For a while there, we were doing 4-10 hour days, so maybe Thursday after lunch. When I was there, all the braze ons were done by Mike Appel and another really talented guy, I don't think they had too many failures.
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Old 06-25-17, 08:08 PM   #13
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well, I'm not Dave and John isn't Dave, but my guess is it was built on Friday after lunch. For a while there, we were doing 4-10 hour days, so maybe Thursday after lunch. When I was there, all the braze ons were done by Mike Appel and another really talented guy, I don't think they had too many failures.
My 1984 610 had to go back to Trek to have the seat post clamp threadings replaced, after a year of light use.

I don't care who brazed it or repaired it, but it's good after that repair. They seem to be the same little barrel fittings used on seatstays to provide anchor points for racks, or sometimes added to dropouts for fenders.
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Old 06-26-17, 10:56 AM   #14
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I repainted a lot of frames during the late 70's and early 80's when these top of the bottom bracket gear cable guides were popular. I kept in my old braze-on bit organizer the guides from frames that had pulled off. Today I counted 5 front bosses and 2 rear bosses that had came loose while the bicycle was in use. All but 1 had brazing material over the entire surface that touched the shell. Talking to the owners that brought their frames in for repair, some of them noticed a small separation at the front first before the whole thing finally came off.
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Old 06-26-17, 11:10 AM   #15
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that's interesting, silver does fail occasionally, generally because the gap is too big.
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