Rusted Out Fender Replacement
You would think that Detroit might get a clue and fix this rust problem on pickup truck beds. Oh, well, this makes for a fun project if you like welding and grindings for hours and hours.
The old rusted out fender after I took off the chrome trim.
Here, I've cut out the rusty part of the fender. Originally, I was going to cut the entire fender out to match the new panel minus 1/2" or so but I was told that the more old metal I left, the less likely I would have warping when I welded. I was going to cut this out to the match the shape of the new panel minus 1/2" and then use a panel flanger to offset the old fender to accept the new panel - making a smooth transition. As I later found out, that "could" have been used at the very top but the metal distorts and pulls inward anyway so it would have been a waste of time. I also rust treaded, primered, and painted the old inner fender to help extend its life.
I used a 4 1/2" Mini grinder with a cut-off wheel.
Later, I will go back and connect the inner and outer fender with a couple of short metal straps and small cap screws. They sell complete inner fender panels as well but that would require the removal of numerous spot welds against the bed and it looked like a huge pain. Doing it this way will maintain the strength while prevent water and salt from being trapped there again.
The new panel. This cost me ~$39.
Place the new panel on the fender and mark around it so you can grind off the paint. Getting the panel in position was a little tricky and required that I hammer in the original fender lip slightly. Also, the groove in the body had to meet with a corresponding angle on the new panel.
After you grind off the old paint along the lines of the new panel, you spray on Weld Thru Primer. This prevents rust from coming back behind the new panel where you weld. I also used an air grinder to debur the new panel so it would lay completely flush and also remove the paint on the new panel at the edge where I was going to weld.
Place the new panel in place and weld. I started in the top center and made about a 1/2" tack. Move out from there every 6" and make a tack on alternating sides until you are around the entire panel. The old fender and new panel fit well enough that there was no gap between them. Where there was a slight gap, I simply pushed against the panel while I made the tack. The long reach Vise Grip pliers worked great along the edges. I've been told that you can also temporarily drill and screw the panel in place but this worked out and I had no warps or gaps.
Notice that I rounded off the corners of the panel. In fact, I rounded off the drivers side even more and had to cut the entire panel down from 40" long to about 36" to fit between the two fuel doors.
What the welds looked like after it's been stitched together with short little tacks. I used a Lincoln mig on the 'A' setting and '2' on the wire feed speed with .023 mild steel rod and C02/Argon mix gas. It never once burned through and made a nice, small bead.
The right side has been ground down flush in preparation for bondo. Lots of grinding so the smaller you weld beads the better. I didn't grind too long in any one place as that could heat and warp the panel.
And finally, shot with Urathane primer and ready to paint - after 3 or 4 applications of bondo. For the first application of bondo, I used the type with the short fiberglass hairs for extra strenght at the weld joints.
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Last updated July 04, 2005