Good evening all. I finally started tearing the interior out of my 79 F250. Other than having two layers of carpet there weren't too many surprises. The drivers side floor pan had a little surface rust that came right off with a wire wheel. I was not so lucky with the passenger side. After cleaning it up a bit the hole is about the size of a orange. The cab mount underneath it is pretty bad as well. After reading thread after thread on floor pans and cab mounts, I ordered them from Dennis Carpenter. This will be my first attempt at putting a new floor pan in. I will be doing this with the cab on as taking it off is not an option for me right now. My question is the sequence. I believe I should remove the rusted area from the floor pan and then the cab mount. Then install the new cab mount followed by the floor pan patch. Is this correct? Or, should I patch the floor pan before putting the new cab mount on?

Thanks,
Will

 

I think youre on the right track. Ive done floor pans in my 72 f250 but didnt have to do cab mounts. I would do it like you said though just to make it easier locating where to put the cab mount exactly in same position.

 

Step one is to make sure and brace/block/shore up the cab (between the cab and frame) on the bad cab mount side. You do not want it to settle when you go to remove it. As far as the floor pan, I'd cut out the orange size hole and weld in new metal and leave as much as of the factory as you can. But since you have to replace the cab mount, I would do that 1st and leave the floor pan replacement or repair for later.

 

Thanks for the insight. I have read hundreds of your posts. I think I may use this as an excuse to buy a decent hobby welder. Right now I have one of the cheap HF inverter ones. Its okay, but I don't want to settle for just okay on this truck. My neighbor is a fabricator who welds my more important stuff who gives me hell for using the HF welder.

 

Does the cheap one weld? Strong versus pretty? Might be a simple adjustment to the settings, a change of wire or stick, material prep, and more practice with what you have. A new welder is like a new GF, you never know how it is going to work out until you give it some use.

What about having the fabricator neighbor teach you a few welding things and let you use his welder? A persons welding only gets better with...well.....welding.

 

simple version

Support the cab so it doesn't move when you remove the body mount bushing. Remove the body mount bushing and any shims. Cut out all the bad metal. Fix the floorboard first. Bolt the new cab mount panel to the frame with the old bushing/shims, if there were no shims, add a couple, weld body mount panel to floorboard/cab. Remove cab supports and see if anything moved, you may need to remove the body mount and adjust shims to fine tune the panel alignment, but it'll probably be fine.

 

Thanks gents. I think I will drag my el cheapo welder over to the neighbors and have him give me some tips. I will definitely need to practice before welding the thin pans in.

 

That is how I would do it.
Floor first all welded up.
Then slip out the old mount and slip new one in and lower the cab and weld it in place.

As for the welder dose it use gas, i am thinking not.
Part of the problem not using gas is the flux core wire.
You have a lot of cleaning up after the welding but the big one is wire size and what you are working on.

Any sheet metal like body patch panels and floors you want the thinest wire you can and you can only get wire for gas.
The thinner wire you dont need the heat turned up high where you will get burn / blow thru leaving holes.

I would say if the welder you have now is not gas and you were ready to pull the trigger on a new one then go with gas and then have your buddy help you "fine tune" you. Better yet pick out a gas welder or 2 and run them buy him and see what he has to say or tell him you have a budget of xxxx amount and see what he can come up with.
You may need to reel him in a little as this is just a hobby for you and you dont need top of the line welder like he dose as his job depends on getting the work out the door.

I have a Lincoln 135 120 volt MIG with gas and love the welder.
I have used it on a lot of things but the last was floors, rockers, cab corners and more on my 81 F100 Flare Side cab off frame 4 year rebuild.

Here is the right side cab mount with the floor removed

I used a air hole punch to put holes around the outside of the panels and then plugged welded them to look like factory spot welds.
Yes I over lapped the floor as this truck is a driver and it was easier to weld.
I did 2 coats of seam sealer top & bottom then 2 coats of roll on bed liner top & bottom to make sure the over lap is sealed.



Dave ----

 

Dave, I'll use any excuse I can to upgrade tools. The biggest problem my neighbor says I have is that the welder does not have gas.

 

Well there you go time to upgrade the MIG welder to be a real MIG welder the G stands for Gas LOL.
As said with gas you can run the thinner wire needed for sheet metal work.
I believe most if not all gas MIG's can run flux core wire you just need to swap the wire leads inside the machine and leave the gas off.

My welder came with gas kit but a lb of flux core wire so I used that first when doing sheet metal work, lot of clean up was needed.
I then used Co2 gas and the welds came out a lot better, cleaner and was happy with them.
Then I moved and got this pick up and knew it needed a lot of welding and I also have a project car that also needs panels so I went with a Argon mix gas and the welds are even more clean & better. I have the Co2 as back up but will go Argon when ever I can.
I do have a roll of flux core for when needed like welding outside and it is windy as the wind blows the gas away and the welds turn out like crap.

One day I would like to get a TIG machine to play with but for now the MIG dose what I need it to.
BTW get a good auto darking helmet, I have a Speed Glass I use.
Dave ----

 

I prefer flux core for panel replacements, with good fit up beads lay nearly flat, did it for a paycheck for years. picked up one of the green hf welders recently, runs great albeit short duty cycle. Have tig at home too, I have a lot harder time with warpage with that, but it is a lot easier to metal work after.

 

MIG will always be better than flux core, as far as finished work goes, but flux core is fine for floorboards/sheet metal, just takes a little more cleanup if you want it to look nice. Get .030" flux core wire, makes a huge difference on thinner stuff. Flux core is also better for outside work when any breeze will just blow away the shielding gas or on anything you can't get 100% clean/rust free.

My buddy bought a HF welder that wouldn't lay a decent bead no matter what we did. I opened it up and found one of the 120V input wires was only soldered on by a couple strands of the wire, which were all blackened. I re-soldered the lead fully on and that thing started laying decent welds after that.

 

A scraper does quick work of a little flux core spatter, anti spatter spray exists too. Mig is at least double the grinding in my experience if you want seamless repairs.