Auto body repair & detailing: crack in frame..95 pathfinder, stress cracks, perimeter frame

Question
Epidemic of frame woes from this year/model..Okay..Cracks are from behind rear wheel susp mounts..Only support back body mount and wieght of rear..Can I gain a few years outta this GREAT truck by using a good frame section from the boneryard?...Nothing vital is in jeaprody...Worth fixin!

Answer
Hello Chris! There is nothing non vital about any area of a perimeter frame- lets be clear on this. It supports the weight of the entire rear section over the weakest part of the body- the rear wheel hump. If you get hit in the rear, the entire rear section will fold downward like a cheap paper box, jeopardizing anyone who occupies the rear seats. I would personally consider this truck at the end of it's life if you are getting stress cracks in the frame- that just isn't normal. I don't know what the sectioning procedure is on your pathfinder, but if the cracks are in front of where the factory says to section it, a safe sectioning cannot be performed- only replacement of the entire frame is recommended. You need to check with a Nissan body shop for where to section the frame. When sectioning a frame, it's common to have to "sleeve" the repair from inside using a left over piece of frame. Cut the frame nicely, grind off all scale and rust to bare metal -both sides- You drill half inch holes along the leading edge of the cut- about 2 inches apart, about 1.5 inches in.  It will take about 5 holes, probably 3 on the vertical surface, and 1 on each horizontal surface. Use a grinder, and bevel the edge of the frame rail- not a hell of a lot, maybe a 60 degree angle. Now, make a sleeve about 4 inches long out of an old frame piece. It will need cut down slightly, and welded back together so it will slide inside the frame channel. Do this for both sides. Plug weld the sleeve into the frame channels through the holes you drilled, but don't weld the cut yet. You weld it after the frame is slid together. rough cut the donor frame section, and slide it onto the vehicle. Check it for fit, make sure body mounts bolt up It needs to fit against the old frame with only about an 1/8 gap, so figure on fitting it several times, using first a cutter to get it close, and a grinder to do the finish work. Bevel it's edge also, and drill holes like you did on the existing frame. Slide it in, final fit it, bolt up the body mounts. First clamp and tack it in- do the plug welds, and bounce around. You don't want to overheat the metal. Finally, seam weld the splice with 1 inch welds- be sure they penetrate to the backing plate!! Weld from the bottom up- heat rises, the weld will be stronger and penetrate properly. I realize this is a very highly detailed, complicated sounding task- but it's my job to keep vehicles safe. If this all sounds a little Greek, or too complicated- have a professional fix it. I highly recommend this anyway. Bill