Fortunately my 71 Dodge Power Wagon project doesn’t have too much rust, other than the floorboards. The previous owner pop-riveted some metal patches in the floorboards and sprayed the repaired area with undercoating. The first problem with this repair job is the seams around the patches were never sealed properly and the second problem is I don’t use pop rivets in a vechicle restoration project.
In most cases rust on a vehicle is a result of water and other elements penetrating a seam on the vehicle and slowly breaking the metal down forming rust. When a vehicle is built all of the seams are sealed with a auto body panel sealant to help prevent water from penetrating these seams. Areas of the vehicle that are constantly exposed to water, salt and other elements eventually give in to this exposure. If you have been around certain vehicles you know the weak areas that tend to rust out. In addition to exposure there are cases where a manufacturer used inferior metal and these areas are prone to rust over time. Enough about what causes rust, let’s get on with the repairs.
I have said before that aftermarket parts for a 71 Dodge Sweptline truck are hard to come by. Most vehicle types offer good aftermarket parts support for restorations. If you need a body patch panel you can order it and have it at your doorstep in a couple days. Not so with old Dodge trucks. I searched the Internet for floorpan patch panels and did find some but they were $160 each. Now $320 for two floorboards seems a little much to me. Granted they did include a stamped section to fit around and repair the cab mount area, but I don’t know if it justifies the price. On Ebay there was a “make a offer” for the floorboard patch panels which I did, and it was abrubtly turned down. So I went to our local steel supply store and bought two 2X2 foot pieces of 18 gauge steel for $12.00.
The first step in repairing the rust damage is to cut the rusted area out. You want to get rid of all the rust and weak metal and leave about 3/8″ to 1/2″ around the perimeter to weld the new panels in. You don’t want to leave too much overlap because it will be difficult to seal on the underside and will just allow water to get in and start the rusting process all over again. Just mark the area to be cut out and use a cut-off disc in a grinder to remove the old rusted metal. Once the metal is removed it’s important that you grind around the entire perimeter so there is a clean metal surface to weld to.