Weld Repair Across Braze Joint?

TC911e · 01-07-2012, 07:22 AM

What problems am I going to run into welding in patches for these rust repairs where it runs across the braze joint at the fender flange (and what do I do about it)?

I was figuring I'd take the top part of the fender mounting flange off to get the rusted stuff out from under it and clear some room to weld in the patches, but when I saw the shiny brass looking joint I got to worrying about whether I'm going to create problems putting it back together.

Mo_Gearhead · 01-07-2012, 07:59 AM

The brazing will contaminate any new weld joint. You will need to cut out/grind away any brazing material and have clean metal to weld.

Or, you can add the new metal and re-braze it (instead of weld) at that particular junction.

Lukesportsman · 01-07-2012, 08:05 AM

As I was about to say: Factories did some odd things back then, like unrepaireable front frames on XKE's, I thought, now days they might have just glued that joint. And I imagine repairing today's glued together cars will require some effort too in future.

I'd be inclined to try and remove all brazed in metal before welding as it will most certainly contaminate if not prevent the fusion. Or clean it all up and braze that area back together. If you can find a good radiator man still (many have passed do fumes and toxins along with reduced need), they are used to working cheap. They are fast and my local (deceased) one was really nice and excited to work on something other than a rusted 78' pickup radiator.

Maybe someone more knowledgeable will answer you, but I (amateur hobby body man) would not weld near that brazed metal.

Lukesportsman · 01-07-2012, 08:08 AM

After re reading my above entry: If there is really good metal and an overlapped flange at repair, you could evaluate repair for body adhesive rather than braze. The new stuff (even in diposable guns now) is really easy and good stuff.

TC911e · 01-07-2012, 10:57 AM

I'm trying to avoid taking the whole flange off (which is what I would expect will result if I keep chasing the braze joint). The area at the top is the only spot with much of a problem, but there it's completely eaten up from mud and such holding moisture up in that corner.

Any one have a quess about how far I need to stay away from it. Maybe I can clean it out to within a 1/2" or so of where I'm going to weld and then just leave a gap in where the flange is mounted.

At this point, and for the foreseeable future, the car is highly immobile so taking it to the radiator guy is probably out. Brazing is just another skill and equipment set that I'm lacking and probably not going to take on.

doublestuff · doublestuff's Garage

Quote:

Any one have a quess about how far I need to stay away from it. Maybe I can clean it out to within a 1/2" or so of where I'm going to weld and then just leave a gap in where the flange is mounted.

I have no practical experience with this, so take it with a grain of salt. One thing you have to be careful of with welding around a brazed joint is you will likely heat the braze enough to allow the brazing material to melt out of the joint and ruin (or at least weaken) the joint. Brazing, for those who don't know, is a process (like soldering) where the base metal is heated only enough to melt the brazing material - you don't melt the base metal. If you subsequently weld nearby, heating the base metal to its melting point, you run the risk of heating the nearby brazed joint up to or beyond the brazing material's melting point. There are heat sink materials that could be applied to keep the heat from the braze joint, but I have no idea if that would work for this situation. All I can suggest is to proceed very, very cautiously.

Quote:

Or, you can add the new metal and re-braze it (instead of weld) at that particular junction.

If you can weld, brazing is not a difficult process. All you need is an oxy-acetylene torch (you can use mapp gas, but I don't know if that would work for something like this). You can even use a TIG torch as a heat source, but again, I'm not sure that's the best choice for something like this. It might be a good idea to consider brazing your repair instead of welding it if you can.

Good luck!

TC911e · 01-07-2012, 03:49 PM

Thanks guys. I was hoping there was some special gimmick for dealing with the fender flange since it seems like a fairly common problem.

dfink · 01-07-2012, 06:17 PM

I second the panel bond suggestion. The contamination would only be directly where you are welding. Brazing will take some pretty good heat so I don't think you are going to kill the the rest of the joint but rust is cancer and unless you cut out every last bit it is just going to come back at the patch. The panel bond is actually strong enough that even if the base metal rusts away the patch is going to hold and instead of heating and oxidizing the surrounding metal more you would likely be sealing it with the panel bond. If you do weld, do little spots welds then cool the surrounding metal and then repeat.