Brazing Flux Question?

[DennyG]

I am doing a 38` Chevy P/U and the entire truck is sandblasted bare. I am in the process of patching/making panels. Lots of pinholes,thats what I`m brazing. I MIG actual patches.
I have had some problems with the flux on brazing rod cause blisters in the body work about 6months to a year after completed. I sandblasted ALL the repairs,but I want some extra confidence that it won`t come back.
In the past if you brazed 10 spots only 2 or 3 would come back.:confused:
Help!!!!! What would you suggest?

[DennyG]

:confused: :rolleyes: Nobody?

[Phil V]

Denny, its not that everyone is ignoring your post. You stumped the panel. I have brazed MANY patches on and all of us older bodymen are familiar with your dilemma. You pretty much touched all the bases in what should be done to eliminate (reduce) problems caused by residual flux left from the braze welding process.

One thought did just occur to me. I have no idea of how good of a brass welder you are but if the brass welds are "lumpy" with voids in them that are filled with residual flux then that could be your problem. When I braze I make sure that the weld is smooth with no pin holes etc. If you grind the smooth welds making sure there is no residual flux left behind then there can't be any problems later associated with flux causing filler to bubble.

Brazing up rust pin holes (even sandblasted ones) is not the best way to cure the problem, especially if you don't have access to sandblast both sides of metal. A rule of thumb is if the metal has rust holes (large or small) you replace at least that section of metal, again especially if you don't have access to sandblast the backside of that metal.

[DennyG]

Thanks Phil. I have it in bare metal and want to get some primer on it soon,so I was fishing for advise before its primed.:cool: I did some research on flux removal on a welding forum and the best method is submerse in 140degree water! Not a good way for a hole cab. Thought about steam blasting but that would get messy.
I have found that if you can let the brazing set for a couple of weeks it will get white "fuzz"-corrostion on it. I assume if I let it age long enough before covering it should be done swelling the flux?
As you know its really hit and miss with the results,I brazed alot on my `Cuda 11yrs. ago and it only came back in 2 places,of course they are both highly visible.:rolleyes: I agree that cutting out and replacing is the preferred method,but some of the pinholes are in some contured areas thet would be difficult to duplicate with my hands and a hammer

[Phil V]

I don't think letting the brazing area sit and "age" will make any difference in the end result. What causes the blistering of the filler is a chemical reaction between the brazing flux and chemicals in the filler. I really don't think that immersing the braze/flux in warm water will have any effect either. I have use a torch to shrink spots that were heat warped from the brazing process and I used wet rags to "quench" the metal while in shrinking and that warm/hot water had no effect on the brazing flux residue on the metal. When that brazing flux get molten then solidifies like glass. Its really brittle where it will chip and crack very easy, but from my experience water has no effect on it.

[Lost in NJ]

First off, stop using the brazing stuff. It is only going to make your restoration harder.

I have a couple of potentially nice parts that are ruined by other people's braze repairs. What would have been a quick simple patch TIG welded in turned into a major large sized patch to go beyond the brazed area. The parts were painted when I bought them so I did not know they were brazed.

Brazing puts a lot of heat into the panel. This causes warpage, keep in mind every weld is a shink point. To fix a the shrinkage cause by a weld you have to do hammer on dolly hits to stretch the metal back to its original size. You can not do this effectively with brazing. Once you braze an area you can not weld with tig or mig unless you grind back to steel. So to undo a brazed area you need to cut beyond the braze. Then there is the whole flux problem. Nasty nasty nasty all around. There are much better and easier ways.

The quick and easy way to fill a few small rust holes is with a mig, a chunk of copper, and a regular welding rod. First back the weld with copper if you can. Then you put the welding rod into the hole and start the MIG arc on the
rod. The rod takes the heat and reduced the burn back you normally see when you start an arc in a hole. Keep feeding in the rod as you weld. This works very well and you will be pleased with the results. A little grinding to level it and a few hammer on dolly hits to correct for shrinkage and you are good to go. BTW, for leveling the welds get the flapper disks for the 4' or 4 1/2" grinders. The flapper disks will also take off the brazing a little more effectively than the a grinding wheel.

Now the above only works for a small hole here and there. Patch panels into good metal is the only was to fix them in metal. If the area is not structural and you do not want to try patch panels, then consider some of the modern epoxies and poly fillers (such as Kwik poly). These new products will stick hard to properly prepared surfaces and will be fairly easy to work with.

The modern products are great, but please take the time to read and follow the directions.

Anyway, some ideas to consider.

[Chris L]

I had a guy in school years ago that brazed in every panel and a year later the whole truck was rotten again..what if you grind it clean,apply metal etch as well as epoxy primer then do your body work.Any ideas on that?

[Phil V]

I have seen guys that were masters at oxy/acetylene steel welding (steel rod instead of brass rod) who steel welded quarter panels on with NO heat warpage. Its all in the right sized torch tip, the right heat range and the right welding technique.

Brazing is NOT going to cause the metal to rust any quicker than any other welding method. I have a mig welder, a bodyshop type spot welder and my oxy/acetylene torches and many times I will still braze a patch on (depending on where the patch is being welded) because I can braze the patch on faster, better with less screwing around compared to mig welding where most people end up with pinholes all around the patch in the mig welds. I have a LOT of experience brazing and I'm good at it (not bragging, just a simple fact). I do agree that TIG welding is the best way to go, but very few bodyshops have a tig welder and most bodymen don't know how to tig weld.