Need good details on welding floor pans

I just finished this project last winter. I only cut out one side at a time because when you remove the floor, that is some of the supporting structure of the car. I just set the new pans in and held them down to the existing floor as hard as I could. Then I marked around them. (I cut some of the new floor out because in them places, the old part of the floor was still good. I only cut out the rusted part but got into the good metal by about 2 inches. ) I cut about 2.5 to 3 inches above the mark because some places you will need that much. Put the pan in again and fit it. Just start trimming a bit then fit again, trim, fit, etc until you get about 3/4 " overlap all the way around. Take your time with this so you don't trim too much! On the rocker side I used a hammer and chisel to remove pan from the rocker panel. I measured a bunch of points off of the floor to the bottom of the other pan, then made sure the new side is the same to the floor. Also check to make sure your doors still open and close correctly otherwise you'll have to put a jack under the rocker panel to gently raise the middle of the car to make sure everything is good. Then I went around and just tack welded everything in. Then double and triple check your measurements, doors, etc and that the bottom part of the pan is tight against the front frame rail. (EVERYTHING!) Then just start welding about 1 to 1.5 inches at a time then move to a different spot to keep the metal from warping. It still will warp a bit but I just kept pounding down the metal to keep it tight as possible. (oh that's another thing, you probably will have to tweek the metal a bit with a hammer or by bending a bit here and there when you are fitting just before welding. You want the metal to be tight to the old part of the floor) After welding the top in and tacking anything on the bottom, I welded up the bottom seam also. Kind of a sob to do and probably wasn't the best job but I figure it couldn't hurt. I POR-15'd everything. Then I put the seat risers in the same way and por15'd them. I seam sealed the seams inside and out with a brushable seam sealer and seam sealed like the bottom side by the rocker with a seam sealer in a caulk gun. Then I sprayed on a couple of coats of underbody coating on everything. There, job done! Now wasn't that easy???

what jasonn said pretty much sums it up. Do one side at a time, take your time. It may be my paranoial but make sure the car s properly supported before you cut. The only thing I would change form what was said is I would not overlap the new pans with the old floor. Butting the two edges together is more difficult and time consuming but is a "better" situation in the end. Lap joints CAN trap moisture, doesn't mean they will, but they can. If you weld up both sides then the moisture has nowhere to go.

I dont know if this is a possiblity for you but an alternative to making alot of measurements down the rocket panel side of the floor is to cut the old floor leaving a 1/4 to 1/2 inch lip along the rocker panel. My floors were totaly gone but there was still about that much of good material along the rocker panel after it was sandblasted. All I had to do was trim the new floor pans so it would lay on top of the lip and it gives tons of welding area and perfect alignment. I might also add that it is easier to trim more off than it is to add some of the new pan back so take your time.

THe only problem I had was I couldnt turn my welder down far enough and I ended up having to place 1/2 tack next to 1/2 tack...welding for any distance longer than that would cause a massive blowout.

When I was done I seam sealed inside and out and used tons of undercoating on the underside of the car. And it looks good!

I only cut one side out at a time also. I dont know if its true but I have heard stories of cars going limp once their floors are cut out. I didnt want to find out if it was true or not

oh P.S: if you are worried about the possiblity of water gettin in the lap joint you could try putting weld through primer on both surfaces.

67coupe351w said:

THe only problem I had was I couldnt turn my welder down far enough and I ended up having to place 1/2 tack next to 1/2 tack...welding for any distance longer than that would cause a massive blowout.

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Make sure you are running the thinnest wire you can get, use shielding gas, do not use flux core wire. Weld through primer in my experience doesn't work unless you are running a higher amperage setting on the welder.