Removing trunk floor - where to cut rear of floor against the tail section?

[340challconvert]

Cutting out spot welds and removing the trunk floor.
The replacement floor would have a lip where it would go under the tail light panel.

I plan on trimming the back of the panel so that it can be spot welded to the top of the rear brace that goes across the back. This way it would butt up against the tail panel
I do not plan to take out the tail panel and will use a two piece trunk floor.
Would this be a good way to handle the install of the new floor panels?

Additionally, I was going to grind down the welds on the bottom only for the trunk lid latch
brace. Can I tuck the new floor under this brace without removal?

I am also planning to reuse the gas tank braces, do the originals go under the tail panel. I want to be careful in not damaging them for re-use.

And; where are the trunk extensions welded to the main trunk floor?
I ground down the sloppy welds that were on top between the main floor and extensions.

Any words of wisdom on this are appreciated since I have not done this before!

 

[Adam]

If I understand correctly, you are going to trim the lip off the rear of the new panels and weld it to the brace; so how would the bottom of the tail panel connect to the trunk floor?

I think you may be able to leave the latch support in place; but I would use a spot weld cutter bit to drill out the existing spot welds, then just weld them back up when the pans are in place.

I do not believe the gas tank straps are attached to the tail panel..

The trunk extensions are welded to the flanges on the sides of the trunk pans.. I temporarily left my extensions in place to ensure proper placement of the pan, and thus the extensions would be correct when they were replaced; good measurements would have also worked.

 

[Adam]

If your existing pan is in good shape along the tail panel, and around the latch support, I would seriously consider leaving it and trimming the replacements to fit.

I would trim the new pans with about a 1/2 inch overlap back there, with the new pans laying on the old metal; and when everything else is where it is supposed to be, I would scribe the new pans with a carbide scribe or other sharp instrument, to produce a nice contour line. Remove the new pans and trim it with a jigsaw or body saw... I wouldn’t use tin snips, it would deform the metal.

When the panels fit in place, edge to edge-with a small gap, I would tack them in place from the top. (Butt weld)
I would then weld it up from the bottom wherever possible to minimize the grinding/cosmetic work needed on the top.

When welding sheet metal I do not try to run a bead, it burns thru easily, and warps the metal. Instead, I do a small 1/4 inch long weld in one place then move to a different area, keeping the heat down. Back and forth a zillion times until completely welded. I also use a wet towel to occasionally quench the area. Doing this I can usually run my fingers along side the weld and feel little to no warpage..

 

[Adam]

Alternately, you could just trim that rear vertical lip off the new pans and use body panel adhesive, along the tail panel, laying the new metal over the old, but cleaned metal. (That stuff is crazy strong) covering the edge with seam sealer.

 

[340challconvert]

Adam, thanks for your thoughts and input.
The back of the trunk floor pan beneath the tail panel where it is welded to the underfloor horizontal brace is very solid. I trimmed the original floor pan in the back up to that brace.
I like your idea of trimming the new pan back and butt welding in the panel. My original thought was to trim the lip off the new pans and spot weld it over the existing lip and spot welds. I would rather not remove the trunk lid brace if possible, but I will start to test fit everything soon.

I have rookie welding skills and will definitely take the process slow.

 

[gzig5]

I've pretty much done it as you have laid out on my '73 Cuda. I cut the trunk floor at the rear cross brace. I had to replace a 14" section in the middle past the brace that goes into the tail panel. Unlike you, I'm a masochist and am fabbing the trunk floor from 18ga sheet. It is a placeholder until I have the time/space to do the whole back end correctly. I've only got $60 in materials into the job but probably 5x more hours than if I had modified a two piece pan. But, I'm learning a lot, I like doing the fab, and this helps get my skill set toned up for the real job in the future. I'm interested in seeing how yours turns out. Right now I've got 70% of the hole covered and need to address the areas above the frame rails on each side, the extension to wheel house interfaces, and the raised section where the filler neck goes through into the tank. The pan was formed by hand on my bench, no brake available.

 

[340challconvert]

You are doing a lot of work fabricating the panels. Nice fab work and certainly spending less money. Would like to see how your trunk turns out!