There was a fair bit of rust damage in the front corners of the floor board area. This seems to be a spot where water accumulates due to the cup shaped design of the support structure under the floor. There are five different pieces of metal in and around this corner that are rotted out, and I will be attempting to repair.
We are looking at the floor area just at the front edge of the door. The floor pan is sitting up at an odd angle because the new 5 speed transmission doesn't fit underneath (the floor pan will be rebuilt for a custom fit, but we are getting off subject).
This is the same area from a different angle, and with the floor pan removed. There are several rust holes visible here, the largest of which is just below one of the three bolt holes near the center of the image. Some of these holes actually had bolts in them when I first got the truck. When I tried to turn them, the bolt heads easily broke off, as the bolts themselves were rusted completely in half. It turns out that this cab was originally mounted on four wooden blocks. One of them was directly beneath this rotted metal, with these three bolts going through it. It seems that the wood gets wet when it rains, absorbs the water, and then holds the moisture against the metal all winter.
This is the same general area just in front of the door, viewed from outside the truck. You can see spots where the metal is rotted clear thru, and much of this metal is so bad you could poke you finger through it. There are actually two pieces of metal here, an inner (which you cant see) and an outer. The two form a pocket for dirt and debris to fall into, which again, gets wet and holds the moisture against the steel. We wont be attacking this piece today, but we will get back to it eventually.
Back inside the cab, the next rotted metal is this floor piece, from the edge of the door on the right, to the firewall on the left. This part is spot welded in place, and forms the mounting flanges for the floor pan. The top half of this piece is in good shape, but the lower half looks like it has been sitting in a puddle for decades. This is a fairly complex piece and it will be difficult to reproduce. But for right now, I just need to get it out of the way.
I drilled the spot welds and just chiseled through some of the rotted metal to get this out. Now you can start to see the dish shaped metal bracket that was underneath. This is the main support for the whole front of the cab. It is heavily rusted, but because it is thick metal, there is still quite a bit left. Good thing, because it would be a challenge to replace.
Next, I will cut off the bad floor extension. I drew a line at a point where I am going to cut, getting rid of all the bad metal, but stopping before we get into more complex bends farther to the left . Everything to the right of the line will be replaced. The metal to the left is in pretty good shape.
I made this cut as straight as I could. That will help me later when I fit the new piece. This is 1/16 inch steel. My pneumatic cutoff tool works great for this.
Now with that out of the way... these are the "bolts" that went through the wooden support block. These used to be 5/16 inch bolts, so that is some pretty heavy rust damage. As bad as this bracket looks in this picture, there is still a fair bit of metal left, and I cringe at the thought of replacing this. So all I am going to do with this is replace the corner that contained the three nuts.
And what does the 75 year old wooden block look like?
Surprising that there is anything left at all really.
Ok, so lets replace this corner. The lines are drawn along some bends in the metal, which dont show up well in this picture. I have treated the rest of this bracket with SEM Rust Mort, which is why it has a white color now. Rust Mort is actually supposed to produce a black finish, but because this is so heavily rusted, it seems to be acting a little weird.
I start with a piece of 1/8 steel the same shape as the original. (Or at least it would be the same shape if I had flipped it over for this picture.) The rusty metal actually measures a bit less than 1/8, but it was probably 1/8 when it was new.
The easiest way to mark the hole locations was to drill out the old bolts (which are rusted into the old nuts), and use the old part to directly mark the hole locations on the new metal.
I love this photo! I was trying to make the holes show up by backlighting the piece, and it came out looking like it is floating in space. It is actually sitting on a ratchet socket (see the shadow on the right) and I am backlighting with a small flashlight from the left.
I then clamp the old and new pieces together and use a drill to mark the hole locations. The holes are then drilled out oversize and I will weld nuts onto the back side.
I didnt really know what the wooden blocks were supposed to look like, but fortunately, they are easy to find on automobile restoration web sites. This set from Jim Carter Truck Parts came with blocks for right and left sides, and new bolts. In hind sight, since I am replacing the metal on both sides of these blocks, I should have used the blocks to reference the hole locations, not the old metal.
I did use the wood blocks to align the nuts. This is a good place to point out that I did not necessarily do all the work in the same order that I am documenting here. The replacement floor extension has already been fabricated, and was used in this stackup along with the new bolt and nut, to align the nut for welding. We will get to the floor extention in the next article.
I did some spot welds with the MIG welder to lock the nuts into position. I need to keep the welds as quick as possible to reduce the heat, and prevent scorching of the wood block underneath. I did a few more, hotter welds after removing he wood.
Then it is just a matter of welding our new piece back into the truck. I did grind the rust off of old metal the best I could, both top and bottom. The clamps I am using here are meant for sheet metal work. I have never used them before and wanted to try them out. They are not ideal, but they got the job done.
With some cleanup work it looks pretty nice. Along with some good metal treatments, maybe it will last another 75 years.
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