Replacing all 4 floor pans in my 1974 with pictures

[lunarkingdom]

Hey!

I finally am doing work on my project car and I though I would share, this was a barn find with a great body but with some inside rust problems from a very leaky front window and no back window or sunroof insert for the last 20 years. I decided to start the work today and so far I am pleased with my progress. I want you guys to know before you look that this is a runner, not a show car but also know I am doing this to the best of my ability with what I have and whatever I need from Harbor Freight. I started on the worst floorpan, the passenger front and it was a total loss so I got to cutting. Once I was through cutting I started cleaning up all 4 edges to be ready to accept the MVP floor pans and so far my experience is that they are a little wide so I have to trim them and use the hammer a bit. I then trimmed them in slowly, my biggest concern is that the transmission tunnel was damaged all along the bottom. Lucky they make them a little taller than they were from the factory. So far I finished fitting the pan then ground all the rust and finally sand blasted everything with the cheapest sandblaster from H.F. and some 80 grit glass balls. After all that I decided to cover everything in rust converter to get whatever was left. I will update as I continue tomorrow and weld in the pan and move on to the other sections. Enjoy and please remember that I will be doing the best I can with what I have, it should last a couple decades once I seam seal it all up. I did start grinding the passenger rear and sandblasted the edges where I am going to cut and weld the rear pan in but I am not going to cut until I have the front pan welded in first for strength so I just treated the entire thing to see what happens when I grind and cut it tomorrow so don't judge me lol. I did the worst one first, the others I will probably just butt weld them in and not do the entire panel, it was brutal to do it that way but I had to on that one. I will be replacing all of the "holes" from the other floor pans as well with the MVP fake holes so they look good but never leak from below. Mine were all rotten to some degree ands were starting to leak.

Some pictures for you:

Edited December 26, 2023 by lunarkingdom

[lunarkingdom]

Day 2.

Finished prepping then welded in the front passenger floor pan. Went pretty well I am happy with the result. Started prepping the passenger rear and got as far as welding in 90% of it. I am really enjoying the but connecter clamps from Harbor Freight, they really helped with everything. Will continue tomorrow in the morning. Updates will be posted tomorrow evening.

PS Do not weld over rust converter, I had to grind it off of the welding surfaces. I googled it last night, lol!

Edited December 27, 2023 by lunarkingdom

[bergie33]

I have to do this on my passenger front pan, using a Walloth Nesch pan. What kind of welder are you using? On the frame rail part, did you drill out the old spot welds and then drill through from below into the new pan, then weld through the holes? I've been wondering about this part of the project and have very little welding experience. 

[James Laray]

@lunarkingdom good job man.   Thanks for giving us step by step updates on everything.  Nice to see some one do these repairs correctly.  I hope you grind down your welds for posterity (I see some cars where they don't grind welds that are out of sight).   

 

 Interesting noting some nightmarish fabrication and repairs on 2002 floors over the years.  There is an inka orange 72 2002 that just sold on BaT with the metal repair panels pop riveted to shock towers that just sold.   Lordy.   

 

 

 

@bergie33 Looks like he drilled out the factory spot welds on the bad floor pans to remove it.   He drilled new holes in the new pans that match up to the frame rail (note where he removed the new pan paint).  Use a MIG welder to run your wire tip into the drilled holes.  This is a rosette weld.  Just fill up the hole, then if necessary grind.   Practice if necessary on spare metal if you need to.  Not hard when you practice and have a fairly decent welder.   You would not drill up through the rail and weld into the pan.   Do it like the factory did.  You weld the pans to the frame rails.   The toughest thing for those new to replacing these pans is measuring and cutting to fit the new pans so you get that tight seem for your butt welds.  

 

 

Edited December 28, 2023 by James Laray

[Dudeland]

6 minutes ago, James Laray said:

@bergie33 Looks like he drilled out the factory spot welds on the bad floor pans to remove it.   He drilled new holes in the new pans that match up to the frame rail (note where he removed the new pan paint).  Use a MIG welder to run your wire tip into the drilled holes.  This is a rosette weld.  Just fill up the hole, then if necessary grind.   Practice if necessary on spare metal if you need to.  Not hard when you practice and have a fairly decent welder.   You would not drill up through the rail and weld into the pan.   Do it like the factory did.  You weld the pans to the frame rails. 

I used Cleco's to pin the pan in place.  Getting the pan to sit flat on the frame rail is a bit of a trick.  I supported the front subframe and hammered on the floor pan until I got it close.  Not my best product but stronger than the factory. 

[lunarkingdom]

2 hours ago, bergie33 said:

On the frame rail part, did you drill out the old spot welds and then drill through from below into the new pan, then weld through the holes?

Yes I did, I made good penetration when I welded from the top BUT when I looked at the bottom it looked crappy as it did not fill the bottom holes in all the way so I went down there and welded a little more. Overkill but it is all going to get slathered in seam sealer anyways once I grind all the welds down.

Welder is a Lincoln electric 100 from 20 years ago with no gas and a half roll of flux core from 2007 and it works amazing if your gaps are not too wide. Settings were B and 2 for the sheet metal and after doing the first two I started welding a lot better. Once I grind it down I am sure I will have to touch up the welds but I am ok with that.

Edited December 28, 2023 by lunarkingdom

[lunarkingdom]

Day 3

 

Finally feel like I am getting in my groove, The drivers front was a lot less work and the rear was comparable to the other side. I started by cutting them both out since the frame rail was still attached. I took care to take out the cut sections in as close to one piece that I could and used the cut pieces to scribe the new pans. I ended up nailing both of them and only had to touch them up a little bit. Pro tip, I had a bottle jack with a rectangle hole for the handle so I used a chisel in the cordless drill to move it up and down to hold the plug piece of the pan into the hole for trimming. Once they got closer to the hole size I just used butt weld clamps for everything. Those things are super clutch for this job, I went and got another set so I could do both front and back at the same time, it helped me weld a lot faster as I could do 3 spots on one then while it was cooling to the other one. Back and forth. I am pretty tired but feeling accomplished, tomorrow I will grind all the welds inside and out then touch them up and seam seal the lot off them up. Hope I get it all done but I will post my results tomorrow.

PS if anyone knows where I can get a new piece for my gas pedal I would appreciate it, I need a new one mine was pretty far gone. There are a few extra pictures of its position so I can put it back as close as possible.

Enjoy the pictures! 😉

Edited December 28, 2023 by lunarkingdom

[JsnPpp]

Nice progress! Looks great!

 

Jason

[Mike Self]

2 hours ago, lunarkingdom said:

if anyone knows where I can get a new piece for my gas pedal I would appreciate it, I need a new one mine was pretty far gone.

Don't laugh, but my Snapper riding lawn mower has a couple of those ball sockets in the linkage for (I think) the throttle--or maybe the cable shifter--it's been awhile.  They have threaded ends that screw into sockets, but could easily be welded onto a piece of bent metal that duplicates the rusted out piece on your car.  

 

mike

[lunarkingdom]

Day 4 (final day)

I started out grinding all of the welding I had done previously on the four floor pans, took about 4 hours and boy oh boy those welds were strong as hell! I had no idea I was overkilling the welds when I put them down and I am glad because as a result those floors are solid as a rock. After grinding the inside I had to do the bottom of the pans and I was dreading it, my hands were still vibrating from all that grinding so I was super sketched out at starting it but as soon as I did, I realized it was only about an hour and a half of work so I burned on. At some point I went to NAPA and picked up some of their "NAPA 4200  brushable seam sealer", 2 cans of black rattle can primer flat black and one can of rubberized undercoat. I then cleaned up my mess and started brushing the sealer on and once I got the hang of it I went to town. It actually looks smoother when you paint it like a crazy person LOL! Once I finished off the inside, I went for it on the bottom. It took about a quart for the entire thing. I slathered it in all the cracks and went double over all the little pin holes. Went back topside when I was done and saw that I had pushed material through all the holes so I grabbed a paper towel and smooshed them all down. Next up was painting the primer on the inside, it went smooth with no issues and the sealer was already dry enough to paint so I finished it in short order. I threw some cardboard down and then hit the bottom with undercoat.

Not bad if I do say so myself, I now have a very strong and well sealed floor pan in my car! Total time for the project is right around 40 hours.
Now to rest before I have to go back to work on the 2nd.

If anyone knows where I can score a gas pedal metal piece to weld to my new floor please let me know.

I hope this helps those that need to do a similar job, its a lot of work but in the end is worth it to do it your self.

Cheers!

Edited December 29, 2023 by lunarkingdom

[lunarkingdom]

A little slideshow recap on all the work with a short video of the inside at the end.

 

[JsnPpp]

Soo much better. No more flintstone-mobile. Nice work!

[tech71]

Yep, I’d sign that off as roadworthy, well done.

Ya know,  add some descriptive text and you would have a great technical article . Hint

 

[joebarthlow]

nice job. thankfully the PO of my '74 replace the floor just before selling to me. I recently paid for a replacement front panel on mine. I wasn't cheap. You saved yourself a lot of money.

[Georges]

Good work!