When Ford was building Mustangs some 40 years ago, the technologies that prevent corrosion in modern cars weren't available. We're sure those cars weren't designed to be around this long, surviving the salted roads, and hundreds of thousands of miles of body flex, suspension cycling, and more.
This is why just about every classic Mustang (or Ford, for that matter) needs some form of sheetmetal repair. One of the most common repairs is the floorpan, again, due to road salt, as well as lack of undercoating, and rotted cowl assemblies that allow water to migrate under the carpet and rust the floor from the inside out.
In the past, repairing the floor assembly entailed several repair sections installed individually. These are considered "short pans." Later, these pans were manufactured as larger repair panels and are commonly referred to as "long pans." These long pans allow easy replacement of the full floor on each side with a minimum of fuss. The downside to the long-pan assembly is that if there's any damage to the transmission tunnel (such as a modified shifter opening) or extensive rust that's above the new pan's installed area, you'll be making custom patches, not to mention the labor involved in cutting out and welding in all the various panels.
The sheetmetal wizards at Dynacorn have created a much better solution for '65-'68 Mustang floorpan repairs by introducing a one-piece floor assembly. As with the OE part, this one-piece floor is stamped out of one sheet of steel, and includes the reinforced shifter opening with mounting holes, preinstalled seatbelt stud plates, rear torque-box upper panels, and seat riser panels. Installing the one-piece floor is similar to the individual panel installation, and we feel it takes even less time since there's less welding to do and fewer welding materials used.
Follow along and see for yourself how easy the one-piece floor is to install and how much better the final result looks, as we replace the original floor in a '66 Mustang K-code fastback being restored/ restomodded at Classic Creations of Central Florida.
There are multiple options...
There are multiple options when it comes to removing the old floor.
We used a reciprocating saw...
We used a reciprocating saw to cut the floor in sections.
Because this particular fastback...
Because this particular fastback was undergoing a full restoration, we didn't have to worry about fuel or brake lines underneath or having to remove the interior.
Make sure your framerails...
Make sure your framerails are solidly supported with jackstands before beginning the removal of the floor.
When cutting around the inner...
When cutting around the inner floor support, be careful not to cut off the end.
You'll also have to drill...
You'll also have to drill out the spot welds between the floor and the inner floor support to separate the two.
The use of a cutting wheel/grinder...
The use of a cutting wheel/grinder may be necessary for some tight areas when removing the old floor.
A hammer and cold chisel were...
A hammer and cold chisel were also used in some areas to help separate spot-welded panels.
As you remove sections of...
As you remove sections of the floor, be aware that some brackets, such as parking-brake linkage or cable mounts, will need to be drilled out and transferred to the new floor assembly.
With any sheetmetal repair,...
With any sheetmetal repair, there will be fringe areas that require the creation and installation of patches. In the case of our floorpan install...
...the passenger-floor-to-firewall...
...the passenger-floor-to-firewall area needed a small patch fabricated, while we also had to create a few small patches along the rear transition panel into the trunk.
Once the surrounding metal...
Once the surrounding metal was ground with a wire wheel and the necessary patches were created and welded in, primer was applied to the bare areas before moving forward with the installation of the rear torque-box tops and test-fitting of the floor itself.
The kit's included rear torque-box...
The kit's included rear torque-box tops must be installed before the new floorpan assembly. When MIG-welding the panel, we had to drill a series of holes around the perimeter so that we could plug-weld the top panel to the torque box.
As mentioned before, any parking-brake...
As mentioned before, any parking-brake brackets will need to be transferred to the new floor. Measure the old floor to determine where the various brackets must go; then weld them in the proper location.
As with the torque-box panels,...
As with the torque-box panels, the main floorpan needs to have plug-weld holes created around its perimeter. A hole-punch tool is used for the thinner metal of the floorpan.
The one-piece floor is installed...
The one-piece floor is installed through the open doorway of the unibody, requiring an extra set of hands and the slight bending/flexing of the floor to fit through the opening. We're using Dynacorn PN 3648C for '65-'68 coupes/fastbacks. Other applications are available for '69-'70 models and for convertibles.
A good selection of locking...
A good selection of locking pliers in various lengths and configurations are your best bet when completing sheetmetal repairs such as this. The floorpan must be secured for the proper fit before welding commences. Don't be afraid to massage the floorpan as needed for the best fit possible.
Once you're happy with the...
Once you're happy with the fit of the floorpan to the firewall, transition pan, and inner rockers, begin plug-welding the floor into place. To prevent warpage of the floorpan while welding, move from one side of the floor to the opposite side, allowing the previous area to cool.
Where the floorpan sits over...
Where the floorpan sits over the inner floor supports, the floor will require holes to be drilled for more plug-welds. Transfer the floor-support location to the floorpan with a scribe or permanent marker...
...then drill through the...
...then drill through the floorpan to expose the inner floor support for welding. Don't drill through the inner floor support itself.
The floorpan's welding is...
The floorpan's welding is now complete. As you can see, there are numerous plug-welds...
...to secure the pan to the...
...to secure the pan to the inner rails, floor supports, and more.
The seat risers included with...
The seat risers included with the floorpan kit are a thicker-gauge steel than the floorpan itself...
so the hole-punching tool...
so the hole-punching tool won't work, and a drill will be required.
While the floorpan and riser...
While the floorpan and riser are E-coated...
...a layer of primer before...
...a layer of primer before welding will help inhibit future corrosion in the area.
Don't forget to install the...
Don't forget to install the rear seat-base retaining brackets. The Dynacorn kit includes new brackets for most applications, but for our '66 fastback, we reused the originals.
Without these, the rear-seat...
Without these, the rear-seat base wouldn't lock into place, so be sure to install them before moving forward with your interior reassembly.
With welding complete, the...
With welding complete, the plug-welds are dressed with a grinder. The welds need to be dressed down only enough to take off any welding slag and make for a uniform finish. Grinding them too far weakens the weld.
In any sheetmetal repair,...
In any sheetmetal repair, the seams of the repair panels must be closed with seam sealer.
The factory brushed it on,...
The factory brushed it on, pushing it into the seam.
You can easily replicate that...
You can easily replicate that look, even with tube-applied seam sealer, by brushing the bead of caulk with a small disposable acid brush.
After the seam sealer has...
After the seam sealer has cured...
...the completed repair is...
...the completed repair is painted and the body is ready to head into the paint booth...
...for a fresh coat of Wimbledon...
...for a fresh coat of Wimbledon White.