Questions about smoothing firewall

[BirdsThaWord]

Hi all! I have the front end off my 'Bird and plan to smooth the firewall soon. I will have no wiper motor (car will never see damp pavement or leave the garage if threatening rain) and will have the a/c lines that I will be adding exit on the pass side under the fender. I've seen a few companies that offer complete firewall sheet metal that is smoothed, as well as a forum member who had one custom cut. My question is this. Should I have the existing firewall cut out and weld the new one in it's place, or have it welded in over the old with beads of adhesive between old and new (this what the member who had one custom cut did)? Also, if I do weld the new one over the old one, will it interfere with the fender alignment (added sheet metal spacing) as the fenders have one bolt that goes into the firewall itself. Lastly, if I go with a Wilwood booster, would you remove the existing threaded (4) bolts that the stock booster bolted on to, or would you remove them (leaving 4 holes for mounting) and have the master bolt through into nuts on the interior? Just trying to plan and want to learn from those already in the know!

[elitecustombody]

cut out and replace,do not cover it up

[absintheisfun]

I cut out the lip around my stock AC evap opening and welded a new sheet over the old using panel bond adhesive between them....I did a butt-load of research on the matter, and found out a couple things that helped me with my decision:

1. Panel bond is actually a pretty damn strong substance. Depending on which one you get and what you are using it for--There are some that are crap, but there are also some that have a tear strength that is greater than welded metal!
2. Panel bond is used extensively in mondern automotive manufacturing. (do a YT search for Fuzor)
3. If you do panel bond, you need to make sure it is BARE metal to BARE metal--any paint or debris will weaken the bond.
4. Prior to putting them together, the factory seam that connects the top and bottom portions of the firewall need to be completely cleaned of the old seam sealer and 40 years of crap that has collected in there. Also, any rust needs to be completely removed or cut out.

I decided to go with the panel bond with a perimeter weld and plug welded every 6" or so. because it suited my goals for the car better (based on my research).

I watched a few builds where the firewall was cut out in patches and new metal was put in. The end result was that to "smooth" this mess, the builder slathered poleyester filler on it and sanded it smooth. Now, on a car that may only be driven on and off a trailer---fine. I knew that my car was going to be driven and driven hard! I didn't want to put all this work into it only to have a crack in my bondoed firewall due to the stress caused by vehicle flex.
In the end, there are a few places on mine that have dots of bondo (plug weld holes) and there are inperfections that prevent it from being perfectly flat, but with the engine in it isn't as noticeable as you might think.

As far as the question of panel alignment, I haven't found any problems with mine. I took the car apart 5 years ago so I don't remember if it had any panel spacers in there or not, but now that I am putting it back together I am using a single spacer on each fender (on top of the 14-gauge sheet added to the firewall.)

In the end, I did what I thought was best for me given my skill level and ultimate use for the car. Do some seaches here, lat-g and anywhere you can to see how others have done it and how it has held up.

Also--with the wiper delete: Keep in mind that in many places it is illegal to drive a vehicle on the road without them and if you have a state safety inspection, you will be failed.

[ErikLS2]

This is what I did, kind of half smoothed I guess. I made a patch piece to put in the hole where the heater core was and butt welded it in. It need some metalworking due to some minor oil canning
but after that and a skim coat of filler this is what it came out with. I'm going to have a wiper motor and a brake booster so I didn't do much with the driver side except weld up all the holes I wasn't
going to use. Sorry but I can't help you on the booster question other than to say make sure you know what you are going to do before you paint it. Ask me why I mention this!

[BirdsThaWord]

Absintheisfun: Funny you replied because you are the one I was refering to when I mentioned a forum member who had a piece custom cut. It really sounds like you've done your homework on this and you mention some really good points. I def don't want a bunch of filler in there that can crack! I'm in Florida, so no worries about inspections. Not sure about the laws on it, but I'll roll the dice on the wiper delete. Thanks a bunch for the great input. You've helped me make up my mind.

ErikLs2: Thanks and nice looking paint!!! Nice smoothing job. I definitely can't see any oil canning in that shot. I wonder if I have striations rolled into the back of the metal if it would help avoid oil canning? That's what they do with flat metal used in metal roofing.

Elitecustombody: Thanks!

[ErikLS2]

=BirdsThaWord;807042
ErikLs2: Thanks and nice looking paint!!! Nice smoothing job. I definitely can't see any oil canning in that shot. I wonder if I have striations rolled into the back of the metal if it would help avoid oil canning? That's what they do with flat metal used in metal roofing.

The oil canning comes from the heat of welding and it wasn't bad and easily shrunk back. You can keep it to a minimum by making small tack welds, cooling the metal after each one and a little work with a
hammer and dolly. You have to go real slow, you don't just weld that whole patch panel in there all at once. Here's a good discussion about it.

http://www.lateral-g.net/forums/showthread.php4?t=30163

[BirdsThaWord]

Thanks Erik. I'm no welder, but will make sure who I hire to do this reads the thread you've posted. I love being able to learn from guys like you who have "been there and done that". Should make for a quick & clean job!!!

[chops101]

Huh?
I never take mine out either if the roads are wet, or threatening rain, and I've been rained on several times.
With zero percent chance of rain, been hammered with frog stranglers.
Might want to rethink that, that is if you live in FL.

[BirdsThaWord]

Huh?
I never take mine out either if the roads are wet, or threatening rain, and I've been rained on several times.
With zero percent chance of rain, been hammered with frog stranglers.
Might want to rethink that, that is if you live in FL.

I had my no wiper Vette for 10 years and treated it just the same. Never got rained on or ran into any frogs. Rain X works great too!

[67speedfreak]

I would cut the area out and replace rather than cover it up.
Here are a couple pics of how I like to do them.

[wmhjr]

Huh?
I never take mine out either if the roads are wet, or threatening rain, and I've been rained on several times.
With zero percent chance of rain, been hammered with frog stranglers.
Might want to rethink that, that is if you live in FL.

I completely agree. I have smoothed firewall, and eliminated heater but retained wiper motor. No washer, but wiper motor. I painted it to match the firewall. I am extremely glad I retained it. I never go out if rain is threatening but I have been caught a number of times. At least twice, no amount of rain-x would have allowed me to continue driving. Rain was too darned heavy. Also, just condensation at night can be a problem. And as someone else said, in many states (such as mine) it is illegal to operate a car without working windshield wipers.

[The WidowMaker]

i put a piece over the top of the existing. mine was the entire firewall though, and most only touches around the outside. i solid welded the outside and placed plug welds on the inside where i could. most of the plugs you see were just welded up holes becasue im an idiot and thought more would touch.

[XLexusTech]

I would cut the area out and replace rather than cover it up.
Here are a couple pics of how I like to do them.

Is that the DSE plate? I have one but havnet installed it yet... if I can do it like yours i will..

[67speedfreak]

No not DSE, it's one of our plates. Thanks

[67 455 Bird ragtop]

I went against the norm I guess and made a cover and welded it over the existing fire wall. I also moved my wiper motor to the outside fender. I live in Fl also and know in the summer it can rain at any time. HEre's how it turned out. Still needs a few touchups.

[John Wright]

Wonder if using a bead roller to make an X on that huge flat area would help give it a bit more rigidity?(similar to the smaller one on the driver's side.)

[evostilo]

I used the DSE, Plate looked nice but i had the body shop fill in the top so the fire wall would be completly smooth not too much filler hope it dosen't crack on me dout it will tho.

[BirdsThaWord]

I think DSE is who's stuff I was looking at. But since I will have no wipers, and since I'll be running a/c line with a bulkhead connector, I think I'll go the route The Widowmaker did. That's about as smooth as smooth get's!!! Thanks for all of the comments. All of you guys do nice work.
67SpeedFreak: Once I get the piece cut, I may come see you to install it. Is that too small a job for you guys?
67 455 Rag Top: Did you make those cradles your jack stands are sitting on? Looks like a great idea!!! Ever have any issues with slippage? Also, what are the two AN elbows that look like they come from the front of your intake manifold?

[67speedfreak]

I think DSE is who's stuff I was looking at. But since I will have no wipers, and since I'll be running a/c line with a bulkhead connector, I think I'll go the route The Widowmaker did. That's about as smooth as smooth get's!!! Thanks for all of the comments. All of you guys do nice work.
67SpeedFreak: Once I get the piece cut, I may come see you to install it. Is that too small a job for you guys?
67 455 Rag Top: Did you make those cradles your jack stands are sitting on? Looks like a great idea!!! Ever have any issues with slippage? Also, what are the two AN elbows that look like they come from the front of your intake manifold?

Not at all ! we can fab the Panel too if you like.
Let me know if we can help.
Thanks,
Brian

[BirdsThaWord]

Not at all ! we can fab the Panel too if you like.
Let me know if we can help.
Thanks,
Brian

Thanks Brian. Should be a few short months until business breaks for me here. Then I can let loose and start buying what all I need and getting stuff like that done. I look forward to seeing your shop!