I'd been restoring my 67 Mustang coupe when I ran into some rust issues. Surprise! The car was actually very solid with barely any rust to speak of but the original fenders had more wrinkles than an assisted living home and they needed to be replaced.
Rather than buying reproduction fenders of dubious quality, I picked up a pair of factory fenders from a guy on ebay. For 150.00 I thought I had found the deal of the century, but it turned out the cost of shipping was going to be 3 times what I paid for the fenders themselves. Fortunately the guy was eventually heading south for a show so I waited a few weeks, he brought them along and we met halfway.
Obviously, 2 fenders for 150.00 bucks means they will probably need some work. And they did. All in all, they weren't too bad. They were straight but one had rust at the top of the fender rather than down low where they usually get rusty. Fortunately, my original fenders could provide good patch panels so I decided to fix them myself and document the effort. Here's what the rust looked like on the replacement fender
I scribed a straight line from the front of the fender to the side with the inner fender well. Using the line as a guide, I made the cut with the cutting wheel taking care to remove only as much of the fender as was needed. I also had to drill out the spot welds where the fender is welded to the headlight bucket.
Once the spot welds were drilled, I was able to remove the cancerous metal and clean up the surface rust on the headlight bucket.
I used the rusty piece as a template and placed it over the original fender. I repeated the same steps on this fender as well taking into account the width of the cutting wheel.
The fun part starts next. You need to take a metal file and slowly trim up the patch until you get it to fit well. File and test fit, file and test fit. Go slow since you can always take more off but it's harder to put metal back.
Due to where this rust was located, I had to test fit the headlight bucket as well to make sure everything lined up, including the hood.
Once I was happy with the fit, I sanded off the paint from the patch and started tack welding the patch to the fender. Only tack a couple of places, then test fit EVERYTHING. Test the fit numerous times to be certain of placement before you start putting lots of tack welds down. Also, NEVER lay down a continuous weld. This will warp the metal due to the heat. Tack welds work best.
Once you get the tack welds done, test fit again and start grinding down the welds.
I've talked to a couple of body and paint guys since I did this and they said that I probably should have primered the fender first and then laid down the Bondo. I mention this so you don't make the same mistake I did. Fortunately, this fender has now been painted for over 5 years and nothing is popping out (knock on wood).
I finished the Bondo with some 800 grit paper and a long board checking to make sure everything transitioned well then I shot the fender with some 2k primer. I didnt have any scratches using 800 but you may want to use a finer grade of paper when finsihing the bondo. High build primer helped me fill in the scratches.
That's it. If you're patient you can do it too. Hope you find this info informative.
