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Old 07-30-2005, 09:57 AM
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A highly stressed area like that is not a good place to MIG since the MIG bead is so hard and relatively brittle. Brazing is a poor substitute, again because it is weaker than the surrounding metal and will eventually break in exactly the same place. You see a lot of old fenders with cracks that were repaired like that and are re-broken. IMHO, oxy/acetylene is the only proper fix of those fender edge tears. No need to pre-drill the crack root. Use a clamp to hold the edges together and run your welding bead right down the center of the crack using standard 1/16" mild steel filler rod. A little grinding and the fix is as strong as the base metal. Although gas welding dumps a lot of heat into the metal compared to MIG or better yet TIG, edges of fenders are almost always in a highly compound curved area which are much more resistant to heat damage than flat body panels. There may be a slight shrinkage dip next to the weld that you can easily tap out but there won't be that dreaded full panel warpage.
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