Driver’s Rear Quarter Dent

When I bought the car, it had a dent in the rear drivers quarter panel…just behind the door.  The tough part is the fact that the area behind the quarter panel is not accessible…so you can’t hammer it back out from behind.

 

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Body tools to the rescue.  Slide hammer, suction cup, “cheese grater”, random orbit sander, and flexible sander.

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The suction cup helped a little bit, but I couldn’t get it to grip in the worst part of the dent.  So, I switched to the slide hammer.  a few holes around the worst part of the dent, and a some gentle slides pulled the dent back to “close”.

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Next up? Bondo!  I learned to do this as a kid while building my first car.  It was a ’68 Mustang Fastback, and we (Dad and I) cut the fender-lips off to install some fender flares and fiberglass side scoops.  The bondo sets up pretty fast in this heat, so you have to back off on the amount of hardener by about a third to have enough working time.

First I lightly scuffed the surface to see where the high and low spots were.  You can see that in the pictures above the light spots are high, and the darker spots are low.  Once I had a good visual, I used the angle grinder and some 60 grit sandpaper pads to remove the paint down to bare metal.

The idea is to smear on the bondo, generally following the desired contour leaving it just a little shy of the finished profile.  Then I let it harden for 10 minutes or so before using the cheese grater to smooth down some very high spots.  If there are still some obviously low spots, then its easy to mix up another batch and fill these, and repeat with the cheese grater.   When using the grater its important to switch directions frequently. Alternate grating at 45 degrees to the length of the ridge in opposite directions (45 left, 45 right).  That ensures that you don’t end up with deep grooves from the grater.

Once the profile was close to begin working with sand paper, the first thing was to use the flexible sander and some 60 grit to begin finding the high spots again.  You want to give the bondo a good 30 minutes to an hour to fully harden up so it won’t gum up the sandpaper.  Using the 3x-life lubed paper helps too.

I flex the sander until it matches the desired profile and gently sand.  The paper will quickly reveal the high spots.  The smaller the width of the high-spot the farther away from a finished profile you are.  If the high spots are very narrow, I’ll switch back to the cheese grater to work a little quicker. Once the profile is generally following the contour, stay with the sander and slowly and carefully sand from as many different directions as possible…always bending the sander to follow the contour.

 

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You will eventually reach a point where you can’t see the surface fluctuations.  At this point I spray a very light coat of primer on the surface and let it dry.  Then I repeat with the sander to find the high spots again.  Anywhere it sands through first is a high spot.  You can also rub the palm of your hand on the surface.  The second pad of your palm below your knuckles is surprisingly sensitive, and can feel the slightest variations in curvature.  I use the sanded primer to train my palm…ie, feel the difference in the high spots.  Then I continue with the sander until the high spots are gone.  This is indicated by feel, and by when the primer all sands off evenly.

 

If you have a low spot that is too low, its best to sand off the primer with 220 on a power sander and apply the bondo directly to bondo/bare metal.  Otherwise, you could end up with a flake at some point in the future.  As you work you want to be sure to feather the edges of the bondo into the surrounding bodywork.

You will eventually get the contour right, and will find pin holes, and other surface imperfections.  These are easier to fix with glazing compound than to try and work with bondo.  Bondo doesn’t tend to smear very smoothly, and it hardens quickly in summer heat, so its hard to work “carefully”.  The glazing compound is better suited to this task.  Again, sand down what primer you can and adhere directly to bondo where ever possible.

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Finally, finish sand up through the grits until you get to 220 grit. All gone!  I’ve left a coat of primer on just to keep the surface clean and rust free until I can get into the paint booth.  I’ll sand off all the primer around the car with 220 right before it goes in.

 

 

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