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Thread: Replacing floor boards, firewall & welding exhaust

  1. #1
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    Replacing floor boards, firewall & welding exhaust

    While I wait to get my stuff to together to starting working on the frame of my car, my mind has been drifting to other parts of the car...most complex being the floor pan and the firewall.

    Here is what i have and my skill level:
    I do have a 220v MIG welder(Lincoln) and TIG welder (Miller MaxStar150 and small argon bottle), but only have real basic knowledge of welding.

    Firewall wise, I'm really interested in one of these...
    http://realdealsteel.com/i-20900998-...-firewall.html
    http://realdealsteel.com/i-20145067-...-firewall.html

    I guess my question here is doing a replacement of the whole firewall vs trying to fill in the holes is a better way to go for a beginner fabricator. This started to come up in my mind when thinking about how to mount the steering column & replace the master cylinder. It seems many need to fill in the steering column hole in the firewall from the tear drop shape to a circle for the mounting. My car also had a treadlevac so I have a Star Trek symbol like outline of bolts on the firewall from the backing plate (not to mention the firewall was rattle bombed black years ago and peeling). The intention is to later install raingear and have hidden A/C / heater lines so there are more parts to fill in or have holes.

    I really like the recessed smoothie firewall, but wonder how easy it would be to screw up as well...I really want to do this myself as well but wonder if this is a job is too advanced to try to tackle. Being the fact that this would be so visible is another concern...

    The other firewall they make sounds "easier" as they mentions installs at factory spot welds.

    The floor pan, from what I remember is primarily the bad area under the rear seat.
    This is the part I'm looking at...
    http://realdealsteel.com/i-20145093-...th-braces.html

    I guess I'm thinking how to go about this. Mounted to the frame? then cut out the old floor, brace the door jambs then weld the new floor in? Writing it out like that makes it sound easy....Being a beginner I really have no clue on the details of putting something like this in. Can someone fill me in?

    Exhaust -
    I will be working with 304 stainless. I was planning to fusion weld it only where I needed to. Ie flanges for the header, hangers and some of the bends needed to go up and over the differential. Would fusion welding be sufficient? The piping I have is 16 gauge. Should I use filler rod?

    What's everyone's thoughts/suggestions?
    - 1957 Chevrolet 4 dr hardtop Bel Air Sierra Gold/Adobe Beige - Purchased July 5th, 2013
    - 1957 Chevrolet 4dr sedan 210 Larkspur Blue/India Ivory Sedan - Purchased Aug 6th, 2012 (not running)
    - 1957 Chevrolet 4dr sedan Bel Air Canyon Coral/India Ivory Sedan - Purchased June 30th, 2013 (not running)
    - 2017 Chevrolet SS Sedan - LS3 - TR6060 - Nightfall Grey Metallic - Purchased April 2017

  2. #2
    Registered Member chevynut's Avatar
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    Quote Originally Posted by hurddawg View Post
    Here is what i have and my skill level:
    I do have a 220v MIG welder(Lincoln) and TIG welder (Miller MaxStar150 and small argon bottle), but only have real basic knowledge of welding.
    I think you'll do best by sticking to the MIG for sheetmetal work. I recommend that if you haven't yet done so, start practicing butt welding and plug welding with the MIG until you're comfortable with it.

    I guess my question here is doing a replacement of the whole firewall vs trying to fill in the holes is a better way to go for a beginner fabricator.
    Personally, if you're wanting to keep a stock-looking firewall and yours is in good shape, I would just plug the holes you don't want. It'll save you $650 and the new stock firewall is probably harder to install than it looks. You can use small round plugs for anything over about 1/4" and it makes it easier to plug them. If you prefer the looks of a smooth aftermarket firewall, just go that route. It's not that hard to install one if you can master the welder.


    The floor pan, from what I remember is primarily the bad area under the rear seat.
    This is the part I'm looking at...
    http://realdealsteel.com/i-20145093-...th-braces.html



    I didn't know they made a floor for a 4DHT...that's a good thing. You're smart going with a whole floor imo.

    I guess I'm thinking how to go about this. Mounted to the frame? then cut out the old floor, brace the door jambs then weld the new floor in? Writing it out like that makes it sound easy....Being a beginner I really have no clue on the details of putting something like this in. Can someone fill me in?
    I would use the frame as a jig and bolt the floor to it. I would brace the body, and leave the outer rockers on if you can. Remove the inner rockers and clean everything up as good as you can for welding. Repair anything else that needs to be repaired. Drill plug weld holes where you need to, being careful to make sure you can weld from that side. Deburr the weld holes. Set the body on the floor and check for fit everywhere. Once you have it where you want it put some screws, clamps, and vise grips in strategic locations to hold everything in place. When you're satisfied with the fit, start plug welding and keep going til done.

    That's probably over-simplified but it gives you an idea. You're lucky that you have these assembled floors to use.

    I will be working with 304 stainless. I was planning to fusion weld it only where I needed to. Ie flanges for the header, hangers and some of the bends needed to go up and over the differential. Would fusion welding be sufficient? The piping I have is 16 gauge. Should I use filler rod?
    Unless you can do all your fitting to PERFECTION, you won't be able to fusion weld it all. I would use some small 1/16" or smaller 308 filler rod with a 1/16" TIG electrode. Some guys use .040" rod and electrodes. Keep the heat low.....like 40A or less. Be sure to practice a lot before trying to weld your exhaust.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  3. #3
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    Lots of questions to answer from your post.

    Let's start simple. Do you have rust damage to the entire floor? You say it's "primarily" just under the rear seat. How is the rest? I wouldn't replace the whole floor to only repair under the rear seat. Or is the rear floor just the worst of it?

    Same question with the firewall. Is what you have in good shape, just needing holes filled and some modifications? You may just want to fill holes and modify what you have.

    Your mig welder will work well for the floor and firewall no matter what you choose to do.

    Tig or mig will work on the exhaust, tig would be preferred there for the stainless. You'll need need filler rod for tig (mig by definition uses filler).

    Sounds like your welding skill level is low. You need to practice by doing. I'd avoid welding any panels that cost hundreds of $ until you get some practice. So start with the simplest stuff and work up from there.

    Edit: looks like Cnut tree'd me. He didn't say anything that I'd disagree with, except that I'd underscore that if the floor isn't damaged everywhere, you can just repair what's wrong.
    Last edited by Rick_L; 03-18-2018 at 05:17 PM.

  4. #4
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    floors

    I would sandblast the floors first to see the extent of the true damage. If it is anything like mine it might look good until blasted then you could have a Swiss cheese floor which would require more than a patch here and there. If you do the full floor brace the heck out of the body before removing the floor. Ask me how I know. Then raise the body up after bracing and cutting out floor and mount the new floor to the frame and move it back under the body and reassemble. I would probably do the floor before anything else. Good luck.

  5. #5
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55chevysedanX4 View Post
    I would sandblast the floors first to see the extent of the true damage.
    Even then you may not see it. The rear long brace is often the first thing to rust out. These floors had nothing to protect the sheetmetal inside the braces. You could blast the floor and the braces may look good, but be on the verge of rusting out. IMO I would replace the entire floor in all but very few cases where you know everything is solid. Plus, it's often hard to make a good-looking butt-weld when replacing a floor pan, and I would not do a lap weld. I don't know, but to me a floor is cheap insurance so you don't have to mess with it again. All my braces are coated inside with Rust Bullet. Personally I'd get a floor with e-coat on it if possible since it will be inside the braces too.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  6. #6
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    welding to e-coat.

    where to buy rust bullet and can e-coat that is on my new floor board be welded through or do I need to clean the area to be welded when I get to that point? I am sure the originator of the thread will want to know as well.

  7. #7
    Registered Member chevynut's Avatar
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    I don't know where you can buy Rust Bullet now but you can probably do a search. However, I'm not sure how you'd use it on an assembled floor. When I did mine assembled floors were $2700 plus shipping and were only available in two halves from one source so I put mine together myself (still cost over $2000), and I was able to put the Rust Bullet inside the braces.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  8. #8
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    I'd think the most challenging part of putting a new one piece floor in a 4 door hard top would be getting the rear door mounting post back in the correct position.

  9. #9
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    Amen to that on the 4 door hardtop.

    Isn't Rust Bullet just a competing product equivalent to POR15? Personally I'd stay away and go with epoxy primer.

    You can't weld through POR15, Rust Bullet, e-coat, or most anything but "weld through primer". And I'm suspicious of the results of that. Just my opinion.

    And just how long and under what conditions do you expect your restoration to last through? Most restorations won't ever be driven in the conditions that led to original rusting. Not even close.
    Last edited by Rick_L; 03-19-2018 at 07:18 PM.

  10. #10
    Registered Member chevynut's Avatar
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    Rust Bullet is a moisture curing urethane similar to POR-15. It's a super-hard and durable finish. POR-15 is supposedly not to be used on clean, bare metal but Rust Bullet can be, per their specifications. I don't typically like using rust converters but Rust Bullet works well inside doors, inside tailgates, and anywhere else you can't get all the rust off. I coated the inside of my doors and tailgate with it and let it run down into the pinch welds. Since I had it, I used it inside the braces too and just brushed it on. I think it's better inside the doors than epoxy.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

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