Smooth Firewall - Cut out or over the top?

[Simmo]

Sorting out my firewall is the next job on the list.

I have read many success stories with guy's using the likes of the ABC panels etc to smooth their firewalls over top of the existing firewall...in the back of my mind I still have an issue with it regarding rust developing underneath it, particularly the welds where most primers will burn off. Climate is not particularly dry here either, want to do this correctly...and one time only!

I have to raise the tunnel for the T56/mod firewall for VA unit and bulkhead/relocate wiper motor amongst other things so hacking things up doesnt bother me in the slightest.

If I cut the original out, will it require bracing? If so where would be most beneficial?

I'm a novice sheetmetal fab guy so advice/opinions of those who have seen it all before would be appreciated.

[scherp69]

When I did mine, I cut out the original and replaced it with a bit heavier gauge steel. When I cut out the old one, I drilled out all the spot welds. I then drilled holes in the new firewall where it met up against the stock bracing and plug welded it there. I have pics on my build thread, somewhere closer to the start of the thread.

[Simmo]

Hi Mike, yeah I read your build thread start to finish the other day...part of the motivation to get back into the shed!

I think I'll go with 16 gauge as well an hopefully it'll be good...I like the way you did yours so I'll most likely use that as a guide, thanks for the step by step guide!

[scherp69]

Thanks for the kind words Chris. I found it was an easy way to do it. I also wanted to eliminate any chance of rust building up from the old metal behind. I was also worried that if I welded over top, I'd end up with an annoying squeak somewhere from the metal rubbing. I'm really happy with how it turns out. Can't wait to see some progress on yours.

[67goatman455]

i would assume no bracing would be needed. since what is being cut-out is just a one layer sheet of metal, there is no actual structural support there. All the support should come from the a-pillars.

[Simmo]

Thanks for the motivation boost Mike!...some progress would be nice, as I'm sure you can appreciate it can be challanging getting everything out of the US and home without being crippled with tax!

Thanks goatman, it's still on the frame so it's "held" together from the mounts too...I think you're right, I'll just wing it and see!

The 68-72 A body is a bit different how the top of the firewall is formed, it's folded 90 degrees to form a crease where it's plug welded together vertically, so I'm either going to have to pic it off an have a new smooth one formed with the lip (bit beyond my skill level at the moment!) or cut out a panel and just butt weld it. I can see why most just go over the top...I'll keep looking until I find a suitable solution

Some more Googling is in order!

[cspecken]

I just had mine started yesterday. Decided to go over the top, had a piece of 18 gauge metal cut out using a template. We used air craft rivets to hold it together and give it a bit of style. The top seam will be welded up where it meets the top of the cowl. My friend who is doing the welding does not think the bottom of the new firewall needs to be welded, but I feel that in order to give it that stock look it should be.


New Firewall

[TheJDMan]

Chris,
In your first post you mentioned primer. When welding, always use weldable primer. Check with Eastwood they carry several types.

[5spd540]

[mikes2nd]

if worried about rattles, I would back fill with auto filler, not the "space" filler from Lowes. Real stuff for cars. It also adds alot of strength.

I am going to fill my boxed frame and possibly my rockers/other areas with the auto filler.

[woody80z28]

if worried about rattles, I would back fill with auto filler, not the "space" filler from Lowes. Real stuff for cars. It also adds alot of strength.

I am going to fill my boxed frame and possibly my rockers/other areas with the auto filler.

Are you talking about a structural foam type filler? I have been thinking about that for mine as well.

[67 455 Bird ragtop]

If anyone is cutting out their firewall to smooth it please see my thread about a small area I need to patch my stock firewall.

https://www.pro-touring.com/showthre...t-gen-firewall

[Simmo]

Thanks for the input guy's, appreciated.

[Bmf5150]

Good ideas

[Bmf5150]

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