I’m building myself a rear rack and grabbed some tabbed rack hardware from my small parts bin that I thought were 4130. I brazed the tabs into the ends of the 3/8 x 0.035 4130 tubes with Gasflux C-04 Nickel Bronze rod. It didn’t seem quite right while I was brazing and the bronze didn’t wet out on the rack tab like it normally would, but I got it to look somewhat acceptable. Figured maybe it was a cleanliness thing, or I didn’t shine up the tab well enough before brazing. Then a thought crossed my mind and I went back and looked at the invoice (from 2022), and sure as sh!t, the tabs are stainless.
Am I screwed? Anyone else ever made this mistake and just went with it?
I need this rack for an overnighter this weekend so I think I’m just gonna use it and hope it survives. But in the long run should I heat everything up again, pull the tabs, clean everything, then braze them in with silver?
I made a similar mistake. I was making a filleted rather lightweight track/rollers bike and used a Columbus seat tube I had bought as a bundle with other tubes. I had what sounds like the same challenge to get the CO4 to wet out and flow/feather into the tube. Some of the challenge was the 4130 BB shell and that the brazing looked ok on that side of the fillet. I ended up scraping the tube and reused the shell with a “proper” steel tube.
If it were a mitered frame tube, I wouldn’t think twice. But with the fact that it is a rack, and these inserts have really long tabs, part of wants to just leave it and see how it goes. There is a lot of bronze in there.
At the same time, my plans this weekend have fallen through so I do have the time to fix it.
Recently had this happen with some front dropouts. ugh. If the rack is for you, ride and see. If it’s for someone else, replace the tabs.
As for a fix, I’m assuming you don’t have extra length to just cut it off and re-attach so, I’d heat the tab and try to remove it like you would an old tabbed dropout. heat the tube as little as possible. As the brass starts to melt, brush it away with a wire brush and extract the tabs. Hang them downward with vice grip or something heavy hanging from them. Then clean up as much as you can and refit new tabs. Use either steel tabs with more brass OR use silver with the stainless tabs. It’s just going to be a lot of fiddly filing and refitting.
I wish there was a more definitive test for what is stainless and what isn’t. If there is a chance it’s stainless (braze ons, dropouts or something) I test it with a magnet but sometimes that isn’t definitive.
Honestly since the tabs are pretty long i’d probably try measuring where they end, drill a 1/8 hole there and backfill with 45%+ silver, with black flux injected with a pipette or something? Then do a colder blob to patch the hole. Some of your tabs look wetted and on all of them it looks like the bronze got in the tube all around the tab. Even without sticking, the space being filled prevents any movement, and the silver backfill would make that very solid.
If its for your own use i think its better this way, you need lots of heat to remove tabs and it often burns the flux/oxidises the inside of the tube, needing annoying cleanup before reinstalling (like for slotted dropouts)
I took them out this afternoon. I knew it would bug me and that I wouldn’t feel confident about the rack as is. I’m glad I did based on how easily they came out.
I have some new (non-stainless) steel tabs on the way. Just need to clean up the tubes and braze them in.
You wouldn’t be able to get it clean inside there. This wouldn’t work well - and you wouldn’t know until it broke so you could see inside again. Silver needs clean surfaces to stick.
It looks like it wetted out to me. Probably would have worked fine.
I usually have my tabs made from 304, which is only weakly magnetic. Looks like that’s what the commonly available tabs are made of. So in the future, check with a magnet.
…and for the original question, some bronzes and nickel silvers will in fact work with stainless. This one worked “less” but will probably hold for the life of the rack. Please ride it as-is if you can. This is important research for the rest of the community!
When I know I have SS, I use 50n (not for lugs) or Nickel Silver depending on needs. I knew there was likely an acid or some corrosive agent that could tell me. I will look into that. The spark test wasn’t conclusive (in my attempt). Thanks!
