Floor to firewall Repair Question.

Remington · Jun 22, 2016

Im working on installing a new full length floor pan on the drivers side but before I do that I need to repair some rusty spots on the toe board/floor to firewall extension. I was considering buying the floor to firewall extension for 68-70 and fabing it to fit my car. While researching this part I came across this video

that suggest cutting out the metal that covers the front torque box so that you don't have that metal to metal space that can hold moisture. The metal on my car covering the torque box is the most rusted area. I just wanted to see what yall thought about this.

Mister 4x4 · Jun 22, 2016

Mine was in a similar state, so I wound up just cutting out the torque boxes along with the front clip [frame & aprons].

They didn't have any replacement metal available, so I wound up using the lid from an old PC on mine as a patch.

QCode351Mach (Scott) made a similar suggestion about using the sheet metal from another torque box as a patch, since the contours and whatnot are the same.

You can do that, or if the repop metal from the earlier models is 'close enough' for your purposes, I'd go with that.

Keep in mind, the e-brake cable will need to exit the passenger compartment between the floor pan/firewall junction and the torque box. If that whole area were sealed (like on the passenger side), then their suggestion might not be a bad idea... but keeping moisture out of that area with the e-brake cable running through it is tricky anyway. Just make sure all surfaces are protected with your favorite epoxy coating, and all should be good.

timsweet · Jun 22, 2016

Having just recently replaced the rear foot wells in my '73 with replacement panels and fabricating a panel for under the rear seat, I had a similar concern.

I took a 3rd rear foot well panel and created the patch for under the rear seat (they don't make a separate panel for that) after it was welded I took Eastman's seam sealer and used it on the gaps. So other than the welds there really wasn't to much metal to metal. But for good measure I sprayed the entire floor with truck bed liner inside and underneath. That might be overkill for dry AZ but better to be safe then sorry.

Safe to say I won't be doing an TV shows any time soon!!!

Tim

tony-muscle · Jun 23, 2016

Check out my floor thread. I had a similar issue. I ended up using a piece of trunk drop off piece. I used that piece because it was the smallest piece I can find with ribbing. However, the ribbing was not a perfect match, but I made it work. I did try the same floor extension you refer to from CJP, the 67-70 one. The ribbing was wider than the 71 so it was not an exact match. I ended up returning it and getting the trunk drop off because I thought it was going to be easier to modify. Keep in mind that the 67-70 floor extension is thicker than your current firewall, which may be a good thing depending what you have in mind. However, being thicker it will be a little harder to bend and adapt to the contour.

To try countering the issue with possible rust due to the two pieces of metal being against each other, I methodically epoxy prime each side and let it cure before welding the next piece. I used seam sealer above and below, plus underfloor spray with the hope to minimize water intrusion.

http://www.7173mustangs.com/thread-muscletang-needs-new-floor-pans-advice?pid=252300&highlight=trunk#pid252300

http://www.7173mustangs.com/thread-muscletang-needs-new-floor-pans-advice?pid=244168#pid244168

Mister 4x4 · Jun 24, 2016

As I was fabricating my PC Cover Patch, I used hammers, dollies, etc., and smashed my own ribs into the same shape as the ones on the torque box, by literally using the torque box as the receiving end. They came out pretty close - but would fail a concourse inspection for sure. :whistling:

Using a trunk drop-off as a patch is a great idea - it's the right gauge metal and the ribs are an added bonus. ::thumb::