The Stovebolt Site Forums The Shop Area Paint and Body Shop Floor Pan Installation?

I need to replace the floor pans in my 54 GMC 1/2-ton and I would like to get some input as to the best way to do it. I already got some new floor pans off ebay and I want to get started right away. Should I butt-joint the floor pans or use a flanged 1/2" lap joint? I know that the butt-joint is supposed to be better for corrosion reasons, but is more difficult. I have a panel flanger and I think that this would be a lot easier. I plan on seam-sealing/priming/paiting both sides either way. My truck will never be outside of the garage in the winter and might see a little rain at most, so I am thinking the butt-joint may be over kill. Has anyone had any issues installing after market floor pans in their trucks? I noticed that that not all the holes have been drilled in the replacement floor pans and I will need to transfer gas pedal mounting bracket as well. Thanks for any input.

Have you got the floor pan supports too? Careful with alignment too. I got mine a too far forward and had to relieve the floor with a hammer to clear the clutch pedal arm.
http://www.chuckthetruck.com/page3.html

Chuckthetruck, I checked out the link you gave and you really had to deal with some serious cancer on your truck! I believe my floor pan supports are OK, but will know better after I cut out my floor pans. I also thought my floor pans were OK until I sand blasted them! I could not tell from the photos whether you butt-welded or lap-jointed your panels.

I butt welded in my partial floor pan but also used a reinforcing strip on the bottom side. I used a 1.25 wide by 3/16 thk steel strip which is available at Home Depot, Lowes, Sears. I fitted the panel in place, then tacked the strip to the bottom of the existing floor sot hat half the width extended into the repair area. This gave the rear floor panel I was installing some support in an area where not existed before. With the panel in place I tack welded it around the perimeter and then to the support strip. I could then weld up the seam ont he inside of the cab. As extra insurance I used seam sealer on all the floor welds and seams.

Hello,
Nothing wrong with flanging and lapping joints. If you have a jewelers torch, steady hands and good eyes hammer welded butt joints are the best.But if your using a mig I would use a flange tool and lap joints. buy some 3M weld thru zinc primer, sandblast the backside of the patch panel(for best adhesion) coat it and the flange area your welding to with this stuff and weld away. I have done this for many many years with good results. Of course most of the trucks I have redone are work vehicles and not perfectly restored show trucks.... Good luck

Well I have the passenger side floor pan all fitted in place and I decided to go with lap joints for most of the panel w/ a butt-joint to join the two floor pans together. One problem I found with these replacement pans is that they are not wide enough and there is a 1-1/2" gap where they are supposed to meet just in front of the seat in the transmission cover area. I am not sure if the front is going to be OK or not, since I now need to remove the old floor section on the drivers side before i'll be able to tell. I will have to add a small piece of sheetmetal to fill in this gap. Has anyone found this problem when you replaced your floor pans. My truck is a 54 GMC, so I wonder if there is a difference in the same year Chevy floor pans. My original floor pans are different from the new replacement pans in that my original pans used a two piece transmission cover and the new ones only use the one large transmission cover. I think this was the way the original Chevy floor pans were. Here is a picture of my original floor pans w/ the two piece cover removed:

http://community.webshots.com/photo/109000222/471261579JmHIAz

From the picture it looks like your truck is a hydramatic truck. That's one reason the floor pans don't match. I don't understand the 2 piece cover though. I have two '54 GMCs, a 3 speed and a hydramatic and both have a one piece cover.

Cletis, Why do you say my truck looks like a hydramatic? When I purchased this truck it seemed pretty much original except that it has a 261 Chevy engine instead of the 248 GMC engine. It also came with a SM420 4 speed. Another thing I forgot to mention about my original floor boards is it also had a third access plate where the brake and clutch pedals go through the fire wall (see the picture I posted above). From what I have been able to find out about my truck I believe it was built in the Oakland, CA plant. I have not seen another floor pan setup like mine either, it's really too bad that I have to replace them.

The hydraMatic trans cover opening cuts more into the toeboard to give access to the bolts holding trans to the engine. The 3 and 4 speed covers are not cut up that high. Cletis has a website that shows both side by side with much good info.

This picture shows that the two after market floor pan sections do not meet in the center:

http://community.webshots.com/photo/109000222/472151436awbuhs

There is no way to move these panels together w/o cutting off the outer edge which fits over the rocker panels in the door opening. Has anyone else had this issue with after market floor pans?

This pictuer shows the floor pans fitted before welding:

http://community.webshots.com/photo/109000222/472151673IHZVAi

Does anyone know a source for rectangular metal pockets that hold the brake and clutch shaft seals in place on these new pans?

cujo, I had the same gap on my floor pans. I just mig welded a strip under the gap,spot welded the top and seam sealed it.Manfighter16

manfighter16, Where did you get your floorpans from? Just wondering if some floorpans/patch panels are better than others. Thanks.

I replaced the floor pans in my 1953 6400 series with pans from Chevs of the 40's. The quality was good, everything fit fine except for the gap in the toe boards. For some reason this must be a common problem. I thought possibly the problem with mine was that I was working on a big bolt, but that doesn't seem to be it. I ordered a lot of sheet metal from Chevs of the 40 and found everything to be of good quality. Everything always seemed to fit in place without a lot of problems. For some items they have a standard piece and one they call "superior". I always ordered the superior, and was always pleased. I'm sure other suppliers have good products. I just got started with them, found everything satisfactory and stayed with them. Allen

do you need to brace the cab before cutting out the old floor pan?

cujo, I got my panels from a small outfit close to my home that sell alot of repo. parts. we have a couple of them close by. I have seen several different panels and they look like the same manufacture across the BIG pond.The panels I got from Chevy duty also looked and fit about the same but were a different color.I did not brace the floors but did cross brace the door openings by spot welding 1/2" square tubing.

I do not believe that bracing is necessary when you replace the front floorpan sections, since the area being worked on is still held in place by the floor section from the front side of seat frame to the rear of the cab and in the front by the firewall. I am going to have to make my transmission cover a little wider due to this gap issue as well.