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Hot Rods Making An Interior Firewall Insulator For '37 LaSalle Coupe

Discussion in 'The Hokey Ass Message Board' started by Carl Hungness, Sep 25, 2021.

  1. Carl Hungness
    Joined: Jul 16, 2018
    Posts: 149

    Carl Hungness

    I have a '37 LaSalle opera coupe and note a new firewall insulator is about $325. They say it is made from ABS plastic with insulation.
    Seems to me I could buy a sheet of approximately 1/8th" ABS cut and heat gun my own firewall cover, and put insulation on the back-side.
    Thus looking for suggestions. I have the old insulator which appears to be made of Masonite and a jute style backing, so I already have a great pattern. I'm concerned about
    interior appearance of course as one can see a goodly portion of the firewall from inside.
    Not sure what type of ABS plastic to buy and have no knowledge of the stuff and my initial internet search seems to show it is available in many thicknesses.
    As far as insulation/sound deadening material goes, there are so many choices available today for interior insulation it's hard to decide. Pricing on the stuff also seems pretty high
    so seeking advice from those of you who have been there and done it. I want to cover the floor and possibly the inside of the doors. The original 'insulation' is still in the car and it
    looks all the world like tar-paper.
    The vehicle is now powered by a '76 Eldorado 500" engine and is in final stages of the build. Here's a before photo. I drove this thing through college and just got it back.
    Here's a photo of the intake (Bulldog) I've smoothed and now powder coated.
     

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  2. Marty Strode
    Joined: Apr 28, 2011
    Posts: 8,798

    Marty Strode
    Member

    Carl,
    On my COE I used grey sound board and jute on the firewall insulator pad. For the back of the cab, I used 1/16" ABS with insulation. I can't find photos of the firewall pad, but here is the back of the cab. Good to see you got it back ! IMG_7299.JPG IMG_7523.JPG
     
    Last edited: Sep 25, 2021
    302GMC and pprather like this.
  3. BamaMav
    Joined: Jun 19, 2011
    Posts: 6,709

    BamaMav
    Member
    from Berry, AL

    That insulation that looks like tar paper probably is. I know Ford used tar paper, asphalt saturated roofing felt actually is what it is, until at least the 1970's in some cars. I had a 1974 Maverick, that's what the trunk divider was, a sheet of regular 50lb roofing felt, or tar paper if you prefer. You could still see the nail lines painted on it! It was also used on inner quarter panels and floors as well.
     
  4. Carl Hungness
    Joined: Jul 16, 2018
    Posts: 149

    Carl Hungness

    Very nice installation..I wasn't thinking about 1/16th stuff until I see what you have done. I can probably use some of it in the interior. Thanks
     

  5. rockable
    Joined: Dec 21, 2009
    Posts: 4,429

    rockable
    ALLIANCE MEMBER

  6. stuart in mn
    Joined: Nov 22, 2007
    Posts: 2,406

    stuart in mn
    Member

    If you have an art supply store in your area they sometimes carry large panels made of various materials, you may find something that will work. Sign shops use a product called Coroplast (it's what that political campaign signs people stick in their yards is made from) - that's another possibility.
     
  7. 1971BB427
    Joined: Mar 6, 2010
    Posts: 8,717

    1971BB427
    Member
    from Oregon

    When I put the SBC in my Austin gasser I knew heat would be an issue inside the cabin. So I used foil backed self adhesive foam directly on the inside firewall. Then I built standoffs that were 1" tall, and made an inside removable firewall cover from 3/8" plywood. I covered the backside of that with more foil backed foam, and then carpet on the opposite side. It attaches with screws, and I have access to wiring behind it if I ever needed it.
    My interior stays cool in all sorts of hot weather, and even without AC my car isn't getting any engine heat transferred.
     
    302GMC likes this.
  8. Tape up your old insulator, lay up a couple layers of glass & mat, trim the edges, pull off the old insulator, stick some new insulation on the firewall side, and glue naugahyde on the interior side. Did something similar in the past; worked good.
     
  9. chopolds
    Joined: Oct 22, 2001
    Posts: 6,208

    chopolds
    Member
    from howell, nj
    1. Kustom Painters

    I love using 1/8" ABS for interior panels, making panels to finish off a trunk, etc. It heats and bends easily, keeps it's shape and is waterproof. For insulation, there is an insulation that is a bit hard to find, but looks like black vinyl or leather. That would be perfect for a visible firewall, over the ABS! I used some on the 61 Olds I did, for underhood insulation. 2016_10300010.JPG
     

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