Due to leaking seals, lack of protective coatings, etc, the cowl / firewall area rusts out on almost all classic mustangs.
This car really need a full firewall. The toe boards were rusted out, and the top flange of the firewall where the cowl mounts is damaged from the previous owner drilling out the spot welds, and the flange is rusted out in several areas as well. The firewall on these unibody cars is what connects the front subrame to the car and I did not want to mess with having the front subrame disconnected from the rest of the car.
As usual, Matt was along side doing a great job helping. Holding things in place, grinding, keeping tools organized, etc.
The thing that makes repairing the flange difficult is that it is 90 degree angel, and has a compound curve to it. So here is a closeup of the corner.
The firewall is thin, so we are using 22 gauge sheetmetal. Cutout a piece the right length and the right witch to math the size of the factory flange.
By doing 6-12" at a time you can matchup the height and curvature of the factory flange. You can see the cut line drawn by laying the patch panel in place and tracing it out.
By cutting reliefs in the vertical part of the flange, the horizontal part of the flange can be shaped to match the factor contour. This is important in ensuring the cowl fits back in place properly.
Flange is partially welded. Once this is complete further shaping of the edge can by done before the reliefs are welded up.
Here is the piece welded into the front corner. The corner had some lower so an od shaped patch was made.