I am replacing my floorboards and it appears that the flange that goes up the side of the cab is completely gone and I believe I need it to spot weld the pans to. What’s the best way to weld in a new one? I’m not sure what it’s called but the part of the cab that’s below the flange looks rusted out as well (indicated by arrow)

 

You will have to cut out the rust, then use a press brake to bend a new piece of metal that goes up the quarter panel/kick panel piece. Not too difficult but will have to fab out of cardboard before you start. If you buy pre-made floor pans, then just add kick panels to them and rivet/weld them together.

 

I have had lots of luck using parts of other scrap panels to assist in this sort of modification. Once I cut out the cancer........i just look at the area to be replaced and envision what the piece would look like that I need. For example: I can see that any piece of body metal that has a 90-degree bend would work. If you have a collection of junk parts, like I do, you can find what you need with a little bit of imagination. In this case I would use the top of an old ford truck fender (67-79), old inner fender, or even an old rusted out hood. These have long 90-degree sections that would be perfect. Find a junk fender, inner fender or hood and your all set. As far as attaching the part with a welder......i would remember that this area will be above the carpet line, so a quality straight weld is demanded to avoid an eyesore. Id stick with straight lines and use an edge to edge "butted" fit. This will allow for a surface that you can grind flat and hopefully avoid the eyesore that most people create because they just don't ask for help.

I have also discovered that working each section (as made by the factory) separately, then welding together is best for my skill level: completing the kick panel first, the floor pan secondly, then joining with a weld after you have straight lines and proper fitment.

My rules:
1. Get rid of all cancer. You should only be working clean white steel.
2, Cut everything to be welded so that you are working with straight lines whenever possible.
3. Remember you are working with very thin steel, and it is not forgiving.

best of luck!!!!!

Lastly......don't be afraid to ask for help from someone with the right knowledge and/or skill set.

 

As said sometimes you just have to envision what the factory had and how you can make it happen with the tools and skill set you have.
Here is the rear cab cross member on my 81 F100 to rocker tie in (cab corner not in place yet). You can see there was a gap were it rusted away that i had to fix to tie it back into the rocker and to the right of that the lower rear door post.

I took scrap and punched holes around the outside and used them to "spot weld" the part in place.

To make sure it was going to be strong I also added to the bottom side to tie it into the rocker.

That area on mine is a little different as the cab support is outboard more to the rocker / kick panel

Almost finished welding

I did over lapping welds by punching holes around the outside of the panels to spot weld them in place to look almost like factory.
Both sides were done the same way and the lower inner & outer left door because of rust.
I then did 2 coats of seam sealer, first coat in picture, over all joints and then 2 coats top & bottom with roll on bed liner.



I rebuilt the truck as a driver, 40 miles to work each way when I want to drive it, not a show truck and use it to take the trash to the dump on weekends.
Only took 4 years on & off and did all the work, even paint myself.

Take your time and ask question it will turn out great too
Dave ----