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Posted by Chris Case @ San Diego on Tuesday, January 01, 2008 at 16:15:13 :
In Reply to: Welding PW Frame? posted by Steve on Tuesday, January 01, 2008 at 15:48:21 :
Mine, and lots of others, crack just forward of the front spring hanger for the rear axle. Between the crossmember and where the inner layer of the frame ends. The crossmember and spring hanger are riveted together, and the inner layer is riveted in, but there is 1" gap between the two, on the top flange. This is known as a 'stress riser'- the one place where it is most likely to flex- zillions of times in the life of the truck. They don't seem to crack at the bottom flange, where the inner layer ends 8-9 inches from the cross memeber. Mine was only cracked across the top flange of the frame, both sides.
My bro-in-law is a certified welder, who works about 99% of his time on trucks. We fabbed two pieces of 1 1/2x 3/16" strap, about 12" inchs long, with mitered ends. I heated them, and used a ball peen hammer over a pipe to dimple them to fit over the rivet, and he welded the cracks and then welded the straps over the 'stress riser' areas. Welded the long sides only, not the ends. The sides were unequal lengths/mitered ends, so the frame had some randomness flex zones. He used stick instead of MIG, since stick has lots more flux for use on old metal. All per the web link somebody posted here, from one of the big truck companies. Plus his experience, and mine in a welding shop.
I'd be careful about doing too much welding on/onto frames. You do want to allow flex. Trying to make some parts rigid with welding only makes the flex all happen in one place- where the fatigue will set in quickly. My tuck had a huge dock bumper welded to it when I got it- bolted to the rear frame, welded to the rear posts, bed sides, and rear fenders. Plus a steel floor welded into the bed. That made the rear more rigid, so more flex was needed at the only spot where it could flex.