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These are various house, car, and bike projects i've done. And more!

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Floor pan rust repair

Posted on May 17, 2021

The previous Battery box repair was just the first step of rust repair i wanted to tackle while the engine was out, and it was a good way to practice some skills forming and welding metal. Since most of the interior is also out of the car, i wanted to tackle the floor pans as well.

I saw some rough metal from under the car, but the top side had been covered up by some galvanized sheet, screwed in at the edges:

floorpan before, covered

It's a nicely formed piece of metal, but a shoddy repair. Removing it gave a better view of the rot:

floorpan before, uncovered

Hard to see the surface vs through rust? A little backlighting helps.

floorpan before, backlit

Other patches included this hunk of steel and 1/2" of silicone. There were a couple more of these, including one covering the hole where the tach cable should have gone (it was going through the oil pressure line hole in the firewall).

floorpan ugly patch

This was the worst section i cut out, but went back further back from there.

floorpan rust

I ended up going just behind the seat mounts, since one of the captive nuts for the seat track had already broken off. This way i'm getting all fresh fasteners. At the footwell, i also replaced the vertical firewall piece up 2-4", since that corner was mostly rotten.

Fully cut out, it looks very bare in there.

floorpan out

I didn't get a pic of all of the parts, but ended up with 2 patches at the toe end of the footwell, plus i replaced the end cap for the rocker panels, which was mostly rusted out too. I also replaced both splash panels, since the lower 1/2-1/3 was gone for both, with other patches of through-rust on the passenger side. 

The hardest part was deciding where to stop, because i was finding small pockets that arguably should be patched in the lower front fender and around the end of the rockers, but i focused on just stabilizing what's there (with cleanup and rust converter) and patching to make it more solid and better sealed to keep what's there in decent shape. I feel confident that it'll be solid for a good while, and that i didn't make it too complicated for whoever decides to do a body-off restoration in the future.

After a lot of fiddly patch fitting and cleanup, i was able to get the welding done. It's mostly plug welded, with several good tacks along edges to reinforce. 

left floorpan welded

The right (passenger) side had a lot of surface rust and some pitting, but not nearly as many holes, and generally more decent metal. Again, it seemed like primarily wet carpet/padding, concentrated in the corners, and the bottom side of that metal was in perfect shape. Everything that stayed got a good rust converter.

right floorboard cut out

This shows the main section tacked in, and the toeboard/firewall patch, similar to what i did on the left side.

right floorboard patches

I painted the bottom of everything before welding and used a weld-through primer at all the joints, then seam sealer on each joint and a good coat of rustoleum on everything.

floorpans done

I removed the driver door and floor high beam switch for better access, so those are going back together now that the paint is dry. I also painted the engine bay (red, to match the main body), which was another big side project but i think will help a lot with the fresh engine in there. 

I'm expecting to pick up all my parts from the machine shop this week, so the next update should be all about the engine assembly.