welding truck frame controversy

admin

Hey all,I've got an old Mack dump truck, Model B, 1965.The frame rail is cracked top to bottom (that's quite a story in itself!) and I'm getting ready to weld it up.  Thought I'd grind out and weld the crack, then grind flush and then weld a big o fish plate reinforcer on it.I happened to see in the truck maual that they DO encourage welding up the cracks, but say NOT to weld the reinforcing plates, but to instead bolt them in.  I'm not sure that I understand why it would be okay to weld the frame but not the reinforcers?Also, I know about heat treated frame members but I didnt think this applies to older trucks.I also undersand about heat and stress crack issues, but I thought that fish plates help with that.  I see lots of different opinions about this, and I know there are some of you guys who specialize in frame repairs and all this stuff.  I'm wondering if there is a consensus opinion about whether to weld or bolt reinforcing plates onto crack repairs.  Any adive would be appreciated!Oh, also please know that I only use this old truck at my place and it does not go out on the road, so there aren't license/inspection issues here.thanks.~martin
Reply:You said dump truck, so is it double framed? where is it cracked at (near the lift cylinder trunnion, near the rear suspension, etc.)? What is the frame thickness?
Reply:You sure can weld it, use 7018.   The last one I did was a 1977 mach, the crack was in the frame right on top, so I ground it out and tigged it using mild steel filler.  On this truck, looks are important because if the DOT saw the frame was welded, they would not like it.  I cleaned it up and sprayed it with Napa rubberized undercoating so it looked like it had never been welded.If you weld the extra plates solid, it will not allow the frame to flex.  This creates MORE stress and will break.Do a search, this has been discussed here quite a few times.David Real world weldin.  When I grow up I want to be a tig weldor.
Reply:IT's to stop the possibility of Crack propagation.  The bolted connection becomes a safety net for your welded repair.   Also a fish plate welded all around transfers the stress in odd ways where the bolted one still allows for a bit of give.Vantage 500's LN-25's, VI-400's, cobramatics, Miller migs, synch 350 LX, Powcon inverters, XMT's, 250 Ton Acurrpress 12' brake, 1/4" 10' Atlantic shear,Koikie plasma table W/ esab plasmas. marvel & hyd-mech saws, pirrana & metal muncher punches.