Some guys are crazy about...
Some guys are crazy about rubber floor mats, but the problem is, if any water gets under them, the floorpan is a goner. Our factory rubber-matted '70 Duster has about as beautiful a floorpan as you'll find in a 35-year-old car, except for the driver-side front that was ravaged by rust. this car had been a four-speed car converted to a Keisler five-speed. This combination leads to an unnecessarily wide tunnel when the original four-speed hump is incorporated. The Tremec features a centrally mounted common-rail shifter, which eliminates the need for the side-offset stock hump. Our plan was to repair the bad floor section and remove the transmission hump, so that we could later modify the tunnel to just the right shape for our Keisler transmission.
With the age of our favored Mopar project vehicles well past the three decade mark, it's a forgone conclusion that some of the steel will have succumbed to corrosion. In the case of our '70 Duster, the overall condition of the sheetmetal was remarkable, however, there was one troubling area that needed serious attention. Our car was factory equipped with rubber floor mats in place of more common carpeting, and that was the source of the dilemma. Any moisture that seeps beneath the rubber simply becomes encapsulated by it, and, with nowhere to go, it gnaws its way through the metal below. We actually got lucky with our Duster, since three-quarters of the floorpan looked like new, with even the original Hemi Orange paint intact. The driver-side front section, however, was totally shot. It might seem odd that only a small area of the floor would have been eaten by corrosion, but the rubber floor covering explains it. Water could easily have seeped into this area of the floor and would have been confined to just that area.
While we can remember seeing floorpan sections creatively replaced with old street signs, we wanted our Duster put back together just as good as new. Replacement floorpans for a variety of Mopar musclecars are readily available from Year One. These partial floorpans are embossed with the same features as the stockers for a factory look. With the ready availability of sheetmetal, the only major hurdle is installing it. There are numerous techniques for doing this type of repair, but we wanted to avoid any tell-tale signs of a replacement. For this reason, the replacement piece was installed to the factory mounting flanges and butt-welded at the joints to the factory metal. We found the pan from Year One matched the original very well, making the installation trouble free. Replacing a floorpan is a fairly ambitious undertaking, but with the right techniques a real quality job can be the result. Here's a detailed look at how we did it.
To eliminate the hump-over-a-hump...
To eliminate the hump-over-a-hump tunnel that we have now, we first cut away the spot welds for the five-speed tunnel, and then the original four-speed kick-out was cut free. A cut-off wheel in a die grinder made short work of the surgery. With the centrally mounted shifter of the five-speed, the entire original four-speed tunnel hump was dead space. We'll fabricate a single-wall tunnel designed to clear the Tremec transmission when we replace the drivetrain.
If the job is only a partial...
If the job is only a partial floorpan, you need to survey the damage and determine what needs to be replaced, and then come up with a game plan. Rust on this Duster was strictly in the driver's footwell, but it was pretty extensive. The factory floorpan is spot-welded at a pinch-weld where it meets the firewall, and, at the sides, it overlaps and is spot-welded to the rocker. We decided to replace the entire footwell section, from the firewall to just back from the rise under the seats. The plan was to install the replacement pan using the factory attachment point at the firewall and rocker, and butt-weld it to the good metal behind and to the side. Overlapping the joints where the new floorpan section meets the old would be easier, but a butt-weld will make for an invisible repair. We marked the cut line with some heavy duct tape to provide a straight edge.
The cut-off wheel zipped through...
The cut-off wheel zipped through the sheetmetal along what will be our butt-welded rear edge. Always check to see what is underneath, since there are many areas of bracing and structure under some portions of the floorpan. We selected our cut line to be ahead of the factory seat-mounting reinforcements.