Firewall rust repair

[littleren]

Cut the battery box out of my 73 Z today and also ended up having to cut about a 6" x 3" section out of the firewall where the battery box butts up against it. My question primarily involves repairing the firewall section. Have the wire harness really close to the cut out section on the right and have a lot of the firewall insulation to deal with as well. Is this an area where, instead of welding in a new piece of sheet metal, I could utilize something like JB Weld to hold a piece of sheet metal in place? I plan on welding in fabricated sheet metal for the battery box but I'm concerned about having to remove the insulation and wire harness to keep from damaging them should I have to weld the firewall section.

Hope this makes sense. I'd love to be able to utilize something like JB Weld since the firewall section is pretty inconspicuous and doesn't really bear any weight.

As always, thanks in advance.

[a7dz]

I do not how you came to the idea that the firewall is not structural. Yes you have to replace the metal and yes you need to weld it in. I even welded a gusset to the back side to back up the pieces. The frame box and inner fender well are all interdependent on the firewall. The firewall acts as one side of the triangle to transfer loads as you move the car.

[littleren]

Thanks for the reply. Obviously I need to replace the metal so if it was somehow inferred from my post that I wanted to simply leave a 3" x 6" hole in my firewall then my apologies (although I don't know how that could be inferred). All I really was interested in finding out is if one could use jb weld to secure this small section of sheet metal as opposed to using my mig welder which will be used on the battery compartment. Guess not.

[a7dz]

The main reason you want to weld in the new metal is to relieve the stress points you created by cutting out the metal. The corners of the cut out will crack. That is why you see rounded corners in all the cut outs. The other thing is JB weld is brittle once it dries and it does not do well with the vibrations. I did not think you were going to leave a hole just cautioning you on the effect of these uni-body cars.

[a7dz]

Here are some pictures of how I did this one. Note the wire harness pass through hole is missing. I too welded it up. Fabbed pieces to redo the fender well and moved on.

[littleren]

Thanks for the info and the pictures. These pictures will help out a great deal. I think I'm going to try to tackle it this weekend so I'll let you know how it turns out.