The Floor Replacement
“I’m not sure this floor is entirely stable”
- C3PO, The Phantom Menace
My trip to St Louis had me bringing a lot of parts home, including the floor out of a 1965 4 door Falcon. What a lot of people don't know is the floor pan for a 4 door sedan, 2 door sedan, and 2 door hardtop are the same floor! Because of this, my poor Chicago car has the ability to have a new floor grafted into it, removing the holey, rusty remnants of its floor that have been beaten on by Chicago winters.
The replacement of a car floor is only a handful of simple steps, but a lot of elbow grease! Be prepared for this project to take time if you are replacing floor sections on a rolling chassis or complete car.
This section is also in My Car section as it is more of a personal fix, and I really didn't research the "correct" way to install a new floor. So please refer to the warning on all of my restoration tips.
What Did I do?
First off I pressure washed the replacement floor. This floor came off of a Raleigh, North Carolina car, and was covered with years of grease and dirt from the road. What was amazing was after the pressure washing the car never had the thick factory sealer applied, but sported it factory primer - the floor looked brand new!
After getting the floor home, I began to remove the subframe members. These cars are all unibody, and the subframe members are all welded onto the floor with a lot of spot welds.
I used a spot weld cutter bit along with regular bits to pry the subframe off of the floor pan. Take your time with this, it can really wear on you. As it did to me.
After the subframe pieces were off, I Cut the new floor to size and trimmed off the remainder of the subframe members with my trusty grinder, "Tito", and eye and hearing protection.
The resized floor was ground down to fresh metal on the edges for good welding adhesion. Now its time to get the car ready....
I checked the weather report and drove the car over to the driveway to cut the floor out. Before cutting, realize that you are removing a VERY important structural part of your car. Your car can literally BEND in HALF if you don't brace the car. As soon as you start cutting, keep the doors closed, or build bars that bolt inside the door jams to keep the car straight. I went as far as locking the doors, duct taping around them, AND placed bottle jacks under the rocker boxes to help reinforce. Also mask off any parts of the car that could be damaged by flying sparks: mainly dash, plastic, and GLASS - don't forget to cover ALL glass!
Now cutting can start. If you have a running car, measure, measure, and measure! Pay attention to where brake lines, gas lines, and subframe pieces are. My car had an "interesting" backyard fix to rig the transmission mount. Instead of using/modifying the stock trans rear cross brace, a previous owner used angle iron and bolted the trans to it, while anchoring the angle to the subframe with bolts running through the subframe, and bolted onto the passenger compartment's floor.
I got a stock transmission mount for a 65 Falcon and modified what was needed to fit. I used grade 5 stainless bolts to secure everything up.
After the floor was removed, I used the grinder to clean up the edges and remainder of the old floor so I have something to weld to. Then, since the floor pan was too big to fit into the car, I cut the pan and fit the pieces in separate sections.
To clarify, I laid the new floor pans on top of the old. This way I have more material to weld to, and I can duplicate the subframe spot welds to the new floor as well, giving me even more strength. If you go the welding route, spot weld every 1 - 2 inches, and move along the floor after every weld, don't weld sequentially in a line. If you do, there is a good chance you will warp your floorboards.
Use your old floor pans you cut out as a practice board. That way you can dial in your machine to weld the new floor. MIG welding is not too hard, but I still strongly suggest you take a welding class. I took one at my local Community College, and learned very valuable information on technique and most importantly, SAFETY.
After the welding with my new Lincoln Electric SP-100T using carbon dioxide, I used a good seam sealer along the seams where I welded, and POR 15 and epoxy paint on the underside of the floor to seal the floor from nasty weather.
Mike in Chicago