To replace or not to replace: roof skin on 77 Trans an - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-15-2017, 08:51 PM
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To replace or not to replace: roof skin on 77 Trans an

I purchased a 77 firebird donor car specifically for the roof. I determined it to be the factory door on the car and for $500 it was mine. Once I got it home I realized that through one of the perforated holes in the under lying roof structure I could see what looked like to be fairly bad rust on the underside of the roof skin.


I decided to cut the he roof off. If nothing else I need the inner structure anyway. My current car has t-tops in it, so the underlying structure is cut up. I have since cut the roof off and am working to decide if I need to replace the skin and I am very much on the French about it. The window lips actually look decent. I took a strip disc to the roof skin and it seemed that there was rust imbedded deeper than just the surface. These are the shiny parts of the skin below that have brown "dots" in the stripped metal.


The really shiny spots in the metal are where I took a 36grit roloc disc to very quickly. I did the same thing to the underside where the rust was on the underside of the skin. I took a very quick pass over the rust that looked so bad in the first pic and it came right off revealing good strong metal underneath.


I feel a lot better after a lot of assessment this evening, but I'm still not sure if it's smart to put this on a $100k car.

My options are to use this roof as is and repair the a-pillars' bases (oh yeah, they're rotted too), use this roof structure and put a new skin on, or buy a complete roof for a 70-73 and modify the skin where it meets the quarters around the rear window since that area is different from the early and late second gens. The benefit of doing this is that I get all new a-pillar skin, a-pillar structure, and under roof. It is a bit of a risk as even the stamping people like AMD don't seem 100% certain that all the other contours are the same.

My main question is what do you guys think of the skin on the donor roof? Would this be safe enough to paint over and do a really nice restore with? If not, what's my best option??

Here are some more pics of other inner portions of the skin.







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Old 03-15-2017, 09:18 PM
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Don't they make repop roof skins? I HATE reproduction parts but this is one I would be thinking about.

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Old 03-15-2017, 10:20 PM
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I vote replace.
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Old 03-16-2017, 04:17 AM
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Well the car will be that much when finished hcompton. I'm doing a pro-touring build.

Yes, they make repop skins. That's what I call "option 2" if you read through the original post. Option 1 being don't do anything, and option 3 being to buy a whole new complete roof with inner structure from an early second gen and modify it to fit my late 2nd gen.

Looks like you guys are saying option 2- replace the skin.


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Old 03-16-2017, 10:24 AM
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In already to heavily invested in this car. Looking back I should have spent more money initially, got a better body, and I would have been farther ahead.

Total fiberglass body doesn't interest me. Maybe doors, but even those I would get in carbon fiber-not fiberglass.

There is a lot of people making pro touring cars out of the second gens and loving them. They're using LS which I plan to do someday. For not I am using a heavily built Pontiac 400. I may move it back into the firewall.

Looks like everyone agrees that the skin needs replaced.


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Old 03-16-2017, 11:36 AM
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I wouldn't give up on it that easy. A good soaking with rust converter would knock down 99% of the spots. Sealing it up with an epoxy primer would do the rest. If it's straight and will work for you use it, no one is going to see it anyway once the body work is done. I did this same thing to my '73 when I pulled the vinyl roof off it in 1979. Cleaned it up, did a little lite sand blasting and buried it primer surfacer. It still looks good to this day. If it's prepped right you will have no problems with it.
The thing you don't want to do on a build like this is get caught up in the "everything must be perfect" whirl pool. Everything doesn't have to be perfect and trying to get to that point will bury you. If it's never going to be seen in the finished product, make it presentable/usable and move on.
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Old 03-16-2017, 12:23 PM
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I think I am in be "everything must be perfect mindset." Did you peel your roof skin up and clean under?

I don't mind the rust being there IF it isn't going to cause problems. I worry that I'll put a $6k paint job on this and in 10 years there will be bubbles on the roof where the rust has finally eaten through. Something like that on the roof would obviously be catastrophic. Is there a product I should use to spray over the surface rust I see on the underside of the skin from inside the cabin to neautrslize it? There aren't very big openings to spray into. Who know what may be in areas where I can't see, but the spots I shown in pictures that look so bad are actually not. The metal is very solid underneath the surface rust, and if I could get to it I am 100% positive I could wire brush it off to a mirror finish and save the roof. Be it as it may, I don't think it will be easy to remove the skin and save it. At that point I may as well use a new skin.

I already have the 400 built. I have about $10k in it and it should make 600hp- it's a standard butler 461 stroker build with KRE aluminum heads and that's what this build makes.

Are you calling he transmission tail support the "K-member?"

So, in summary, I have no problem using this roof if I know it won't rust out from under the paint in 10 years, and I don't know if I can guarantee that. The car will be garage kept and all. Of course I'll properly prep and paint he outside but the underside of the roof skin in between the roof structure is the problem.


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Old 03-16-2017, 05:09 PM
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I actually do have it on a rotisserie, and I love the idea of getting a rust converter in there. You had my hope up! Then towards the end of your post you're suggesting the skin replacement again! Darn it.

I should probably just bite the bullet and replace the skin, so I have peace of mind and nothing to worry about.

Here's another problem with replacing the skin: the a-pillars are part of it but they're not part of the replacement repop skins. This means you have a weld seam on the apillar where you marry the new roof skin to the old apillar skin!! Since this seam has apillar structure behind it you can not dress the weld. This is also another big hold up for me because I see these as being vulnerable to rust too.


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Old 03-16-2017, 06:41 PM
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Btw, when u say k member are u talking about the entire subframe or the 1 portion/bar that holds the engine up??

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Old 03-16-2017, 10:04 PM
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Thanks for the info. I am familiar with BMR. I was confused why you meant since the k member is part of the subframe. No, these k members do not come out. You can get really nice aftermarket subframe, but supposedly the geometry on 2nd gen subframes is a lot better than on the first gens. I upgraded the control arms to tubular, got coil overs, bigger sway bar, etc. and am going to run this slightly modified sub frame. If I do an earlier 2nd gen build some day like I plan to I will buy an aftermarket subframe from speedtech.

Anyway, I guess I might just buy a new skin to be safe. As far as butt welding he new skin to the skin in the a-pillars with weld thru primer goes; I do not like this. Every time I have used weld thru primer it gives me ****ty welds that just weld cold and contaminated. I can't weld thru, on, or near it as advertised. I think if I'm trying to butt weld 2 pieces of 18-20ga steel together and both edges have weld thru primer on them I'll be screwed and the weld will suck. This really leaves me with no options to protect the back of this weld on the a-pillar.


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Old 03-19-2017, 07:27 AM
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............ This really leaves me with no options to protect the back of this weld on the a-pillar.


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You'll be dead by the time humidity moisture and condensation rusts thru from the back side of that weld.

That's what all the surface rust on the roof bottom is from.
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Old 03-19-2017, 07:53 AM
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You'll be dead by the time humidity moisture and condensation rusts thru from the back side of that weld.

That's what all the surface rust on the roof bottom is from.
Exactly, that roof is 40 years old, was bare metal when built and it now only has light pits. I would clean it off with 80 grit, clean well and epoxy prime it. Just for assurance, you could overcoat it with a single stage to be certain no moisture will penetrate it, but like Pugs said, you and the rest of the car will be long gone before that rusts thru.

The concern about rust should be focused on what is on the outside. That will need to be dealt with in detail to be certain it won't grow and bubble under the paint, but the new epoxy primer/sealers seem to be doing an amazing job of not letting old rust in pits grow again.

And since the thread is already convoluted from the original question, keep the 400. You already have a well respected, expensive and powerful engine, why replace with a belly button engine everyone has and are going too ? The car is a Pontiac, keep it true blood.
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Old 03-19-2017, 08:47 AM
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Thanks for the replies guys. I managed to split the roof from the skin. I did so in such a way where I actually think I'm going to be able to reuse the skin. Turns out the rusty spot I posted pics of was the worst spot. I could have cleaned it through the little hole in the roof structure and been fine. Had I done that though I would have always been unsettled and worried about the rust in areas I couldn't see. Now I'll be able to patch the base of the a-pillar skin that's rusted and dress the back side of the welds. I've also taken the a-pillars from my old roof to patch the rusted out a-pillars from the donor roof. I've split the a-pillar stampings since I'm already this deep, and in going to epoxy on the inside. I cut the posts in a spot where I can see both sides of my weld, dress, and paint.

I know you guys probably think this is all totally unnecessary, and I agree! But me just knowing there is an undressed, I coated weld somewhere on the car drives me bonkers, and makes me feel like I did something half way. I can't have it. I've never seen a roof swap done this way, and I am proud- even if the measures I've taken are unnecessary.

I started the swap by drilling all the welds out from the base of the pillar where it mounts to the car instead of just hacking through the pillar like everyone does. This method makes you weld around the pillar so there is undressed weld on the inside and you lose factory geometry- even if it is by just a couple millimeters. Yes, I know that's being awfully anal. Anyway, here's where I'm at and what I found this weekend.



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Old 03-19-2017, 09:04 AM
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Your anal-ness is to be commended.
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Old 03-19-2017, 09:35 AM
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Your anal-ness is to be commended.
LOLOLOLOLOLOLOLOL


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