I have been fighting rust on the floor of Dragon. The rear part of the floor, under the seat is pretty good, but there is some rust, mainly where seams come together. The front part of the floor is intact, but does have a lot of rust pitting in some areas, driver side a little better than the passenger side. There are some pin holes in the passenger side.
This is what I have been doing to remove a lot of the rust.
Let me back up two weeks. I have a carport, that I can part vehicles under. Sometimes the roof leaks a little water, but generally, things stay dry under the carport. the floor in the carport is gravel, and dirt. My garage, stays dry, has a wood floor. It is an old garage. This time of year, I try to do most of my work in the garage. I had to do some work on Ratsun, in the garage, so Dragon went out into the carport. Dragon had some bare metal on the floor, and other areas of the cab. Long enough story cut off, some snow got blows in to Dragon's cab, on the bare metal floor.
I noticed something interesting. Where the metal was bare, and clean, there was very little new rust form the melted snow. Where there was pits in the metal, with phosphoric acid treated rust, there was a lot of new rust.
First tool for removing rust. A drill and wire brush. I have noticed if you slow the drill down, the wire brush digs deeper in to rust pits. This particular drill only locks on at full speed, the hose clamp on the trigger allows me to run the drill as slow as I want. I also read, that if you reverse the drill every so often with a wire brush, it helps to dig the rust out of pits too. Running the drill in one direction, eventually bends the brush bristles over, and they smoothly slide over the rust pits. Reversing the drill makes the ends of the bristles dig into the rust pits. By running the drill slowly, I would often see a cloud of red dust come out of the some of the rust pits.
Second tool for removing rust. Steel wool, small stainless steel detail brush, and phosphoric acid solution. After using the rotary wire brush on the floor, scrub with the detail brush, and it will work more rust out of the pits. It also will make the pits with rust in them, darker that clean metal. Then you can go back and wire brush again. And acid treat again, and repeat. This is a slow and tedious process. this picture is actually later in the process than the next picture.
I think there was a slight improvement, this was the first time I acid brushed, and wire brushed the floor.
Finally, I got to a point where I cleaned up, and wiped up acid. While still wet, wipe acid up with paper towel. Then I spray a solution of Dawn dishwashing detergent, and water on the treated area, scrub that with a nylon brush, and wipe that up with a clean paper towel. Then dry the metal as quickly as you can.
A final wire brushing,
These are abrasive nylon brushes. They do a really good job of removing paint, and light rust. After the final wire brushing, I use tthe grey one to go over the whole area again.
The Nylon rotary brushes get the floor ready to prime. Now, I take a shop vacuum, and clean up some dust and other debris. Then blown out with an air hose, and vacuumed again. Then wiped with a paper towel, very wet with the reducer you are using in the primer, and before it dries, wipe with a second dry paper towel. When either paper towel gets dirty, get a new paper towel, keeping the first wiping towel wet. If you leave wet dirty reducer on the bare metal, it does no good in cleaning the metal,because when the reducer evaporates, it leave the dirt behind.
Finally I primed the floor with PPG DPLF, mixed with activator, and reducer. Again, I just used a brush. This is not a visible panel, on the outside of the truck, I just want rust protection. All this was done a week ago, and las night, I did a second coat of primer on this area of the floor yesterday.
That was just the front half of the floor, driver side. During the week, I did the same process to the passenger side of the floor, but I also dug out seam sealer, with rust under it, from the back side of the passenger side of the cab. That area got primer on it yesterday, too.
I got a second coat of primer on the front part of drivers side of the floor yesterday.
I got the passenger side of the floor primed, first coat yesterday.
I am still digging seam sealer out of the rear of the cab where sheet metal pieces come together.
It looks to me that when Datsun spot welded these cabs together, they did not put primer on the metal before seam sealer. After 40 years, the seam sealer cracks, or degrades, and that allows water into the seam, and rust starts. The problem with rust is the red rust takes up more space than the metal does, and that forces the seam apart, or forces more seam sealer out of the joint, and exposes more metal to rust. Also, once rust starts, it feeds itself, and makes the good metal rust even faster.