Drill holes at end of cracks
Hi Jordan
Generally when fixing cracks what I've done first was drill a little hole (1/8inch) just beyond the end of the end of the crack which helps stop the progression of the crack. Another thing I was taught by an experienced body guy, was when putting in a patch was not to use square corners if possible, instead use rounded corners. He explained that if you put a sharp corner in and weld it you will have a stress point that will want to crack.
I've had cracks like this on the fenders of CMPs and some of them had been brazed. One of them I just went ahead and brazed again, only to have it crack again, some 20 years later.
On my Pattern 12 one of the fenders had been cut and brazed, and it did not want to Mig weld. In the end I ended up cutting and grinding way the old brazing material. In one case, just took the plasma cutter and cut the crack line out leaving 1/8th inch gap. Cleaned up the plasma slag which you really need to do anyway and it welded pretty good with Mig welder.
On lighter gauge sheet metal like automotive it has been more problematic. On the Lincoln I've been restoring a lot of the body seams had been what appears to be brazed. But I'm not sure what the yellow metal really was. Those just didn't want to weld when new sheet metal needed to be added, in the end I just cut it out and replaced it with a larger patch.
Cheers Phil
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