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Street Race Truck More... The Toolbox

Floor Panel Replacement on a 1960's Classic

3/19/2020

Committing to a full restoration project can feel like climbing Everest. If your first steps are a battle against rust damage it may seem even more overwhelming. To a beginner, like myself, replacing sheet metal might seem like a job best left to professionals, but investing in the proper tools and having help from a good buddy or two can quickly restore any lost motivation on your project. The bottom side of your car is one of the best places to start on if you want to get better working with metal. Have patience, take it one step at time. Give yourself a weekend or two with a project like floor pans. You may even work up enough confidence to start on your fenders or quarter panels!

The Tools:

Before diving in, equip yourself with the proper set of tools – other than your skill level – this is a requirement. Look for a medium duty mig welder that can accept a gas connection. Also required: an angle grinder, ample cut off discs, and flap discs are perfect for final shaping and smoothing welds, which can be sourced from a local parts store – get a few. Have a set of 1/8-inch clecos or pinch clamps – essential for welding a solid joint. Also helpful are a good set of sheet metal pliers and a spot weld drill bit.

This 1963 Impala was no exception to rotted-out floor pans. Our first step was locating problem areas like toe boards and other thin areas throughout the underbody.

Not everyone has access to a lift or rotisserie but replacing smaller panels like the floor pans can also be tackled from the interior with the body on the frame. This project is getting a new frame rolled under it after the underbody is complete, so the body was removed. We mounted the body to a sturdy homemade rotisserie, it was completely sandblasted and sealed with a 3-part epoxy before starting the patch work.

On to the Patchwork:

Start by tracing out your problem areas – we’ll be showing you how to butt weld the new panels – this is both cleaner and stronger than a lap weld. Keep in mind it’s much easier to cut and weld down a straight line so make your tracing guide the same. Prior to cutting, rough fit your patch panel making sure it covers the problem area. You’re ready to start on the removal work. Drill out any spot welds attaching cross bracing and remove them.

Next, cut along your guide and remove the panel. After your panel is removed, run your grinder over the cut edges to smooth out any burrs or rough areas before fitting-up the new panel and tracing your marks.

In theory, think of the following steps as a two-part process trimming-in the new panel. This takes a little finesse work and patience, but practice makes perfect. Start by tracing-out the bad metal roughly ½-inch to 1-inch oversized and cut the new panel to fit. Then attach the panel and retrace guide lines with a bit more precision.

Fit the new panel in place and sink a handful of self-tapping sheet metal screws along the perimeter edge about 4 to 6-inches apart. Tight is right, especially when welding. Make sure your seam is as tight as possible – don’t be afraid to bring out the dead blow to massage needed areas.

Once your panel is secured tightly, retrace the edge to draw your final cut line. Remove the panel and use your angle grinder to trim the perimeter edge down to the outside guide line edge. Use a fresh flap disc here – this should be as precise as possible. You’ll want no more than a 1/16-inch gap to achieve a solid weld. Check fitment, repeat trimming if necessary.

Once your panel is trimmed, have a buddy help hold up the panel and begin tacking it in place. Continue tacking the perimeter about every 4 to 6-inches. Use Cleco fasteners, or pinch clamps to bring your edges together tight and consistent. Finish stitch welding the entire perimeter seam.

Reattach your cross bracing by spot welding the original mounting locations and finish your seam by smoothing out your welds as desired. We applied a very thin coat of filler to smooth out any unevenness across the new panel.

After a few late nights and a weekend or two our underbody was patched up and ready for undercoat.

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