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To replace or not to replace: roof skin on 77 Trans an

13K views 255 replies 8 participants last post by  idrivejunk 
#1 ·
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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#6 ·
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.
Mark
 
#7 ·
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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#8 ·
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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#10 ·
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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#11 ·
............ 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.
 
#13 ·
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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#17 ·
I don't think it's futile. I think there are real gains. Were the gains large enough to justify the work? That's probably the debatable part, but the efforts were definitely not futile. Gains have been made with success- so far.


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#18 ·
Perhaps I should rephrase that. I had also typed "I get what you're doing." but backspaced it. Even if part of the work may outwardly appear to be senseless to some, you have satisfied your quest which is simply to know what you're driving. I get that, and its not as unusual or crazy as you may imagine. You've obviously come to view welds as simple fasteners, as they should be IMO. That takes away the boundaries of what is feasible and leaves you wide open on your car, to decide how. The things to bear in mind are all the remaining untouched seams on the car. As always, its your call on your car. Enjoy the project!
 
#20 ·
Well fellas I'm trying to prep these two pieces for the SPI epoxy primer I just got in. I've started stripping with a DA sander, 2" die grinder strip discs. 2" die grinder 80 grit roloc wheels, 4.5" grinder strip disc, and 2" roloc strip discs. After about 2 hrs this is where I am on the inner roof structure and underside of the roof.




I'm already wondering if there is a better way. Are there any chemical strippers I can use that will not affect my SPI epoxy primer? Can I carefully and lightly sand blast the inner roof structure without warping it? The blasting is what I'm leaning to. I plan on grinding and using all the methods I mentioned above to remove the paint and rust from the actual underside of the skin because I think blasting something like that would inevitably warp since there are no ridges or anything to make it sturdy.

Also note the black, embedded rust on the underside of the roof skin that I have already made passes on with the 4.5" grinder stripper disc. Is this the type of rust that requires an OSPHO assault?


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#21 ·
I wouldn't hesitate to blast the inner structure at around 70-80 lbs pressure. There are enough beads and bends to hold that from warping.

I know Barry doesn't like rust converters under his epoxy. Others have removed the pits with Ospho and wire wheels before the epoxy. I haven't been brave enough to try any acid based cleaning under paint, as I have no experience with acids and very little with paint. I did blast and SPI prime/seal the bottom of my floor pan before paint and it all seems to have worked well.
 
#22 ·
The dark red primer might wipe off with a thinner rag easier than sanding. If I were you, I would use 40 grit on a 6" DA to start. Do the heavy work with that, then switch to 80 grit. Also worth mention is the pattern your DA has. Using one with a coarse (big) orbital pattern will strip faster than one that has a finer pattern. You want a rattly harder to hold DA for rough metal stuff and a buzzy smooth sanding one for finish work such as primer and paint.

As TMP said, the inner structure is screaming blast me! I'll leave the rust treatment advice alone but the inside of the roof skin looks like it might be OK with thorough sanding, cleaning, and just epoxy. Moisture can't land on upside-down stuff.
 
#23 ·
Gosh I love this forum. I get anders almost as quickly as picking up the phone and calling someone!!

Anyway, yea, I think I will blast the inner roof structure. I think I'll have to strip the underside of the roof skin with various grinding and sanding pads. While DPI doesn't really "like" ospho under their epoxy, they say that if you use it, reactivate it after it dries, and then rinse it off with water you should be fine. I of course err on the side of not taking risks, but being as this is the under side of the roof and in a place where not even I will see it, much less anyone else, I think I would try the ospho treatment. That being said, is this kind of rust where one would use OSPHO? I see threads about people using it on "surface rust," but I don't know what that ever is and how severe it is. So the question stands; is this dark rust, that seems to be below the surface, something that I should destroy with OSPHO? Yes, grinding and wire wheeling would probably take care of it, but being as these skins are 20ga (.033"-.037"), I hesitate to keep grinding more and more meat away.

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#33 ·
Being that its on the roof I wouldn't even worry about epoxy priming the inner structure if you use ospho, that alone will not only remove the rust but it'll seal it up and keep it from rusting again. As you can see it never had any primer at all from the factory and it lasted quite a while. The deeper rust will need going over a second time after it all dries with a wire wheel and ospho reapplied a second time. rust wont come back and you can weld through treated metal easily.
If you really want to epoxy it then a good scuffing with a red pad will be good enough just wipe it good after wards with a water born W&G remover Rinsing with water is a good idea for other areas of the car but not that part
I don't know who you talked to about the primer reactivating the ospho THATS a new one one on me and makes no sense at all.
 
#24 ·
Thanks for the product suggestions. It seems when doing this kind of work knowing what products to use is 2/3 of the battle.

When I said I was using the 2" roloc discs I was using them on a die grinder by the way, not on the DA haha. Anyway, I'll try the brass wire wheel. I have a cup exactly like that from harbor freight but it's in steel. I'm also going to talk to SPI and see why they say about chemical stripping. I'll report back here.

I do need to buy a box of the maroon Scotch brute pads. They're mentioned so much. I know I could use some. I've been getting by with the small stripper discs for the die grinder.


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#26 ·
What type of sand do you guys suggest to use on blasting panels? In the past I have just used typical cement mixing sand from my local concrete distributor.

Also, I notice when I look for ospho that some is green and some is black. Is there a difference between the two? Which kind do I need to neutralize the rust?

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#29 ·
Is the use of normal sand bad for the part or is it not recommended due to the danger of inhaling silica? My next question is; why is inhaling silica a concern? Can't I just wear a dust mask? Problem solved- I would think


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#30 ·
Silica in your lungs is like asbestos over time. It doesn't break down or go away. It is known to cause cancer.
A dust mask will prevent the larger particles from entering. You would still be inhaling the minute ones.
A painters mask will be much better.
Sand isn't as hard as black diamond type particles and doesn't penetrate as well. Sand will work. The job will be quicker and the outcome will be better with a harder particle.
 
#31 ·
Thanks for he info. As usual, expense is making me steer away from the good stuff (black beauty). It looks like it's $1/lb. I have to drive further to get it too. With how well sand works I'll just stick with it and take precautions so as not to inhale it. I'm glad I found out about the dangers of it. I've sand blasted a couple times and never taken any precautions to avoid inhalation.


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#34 ·
Deadbodyman, I'm slow, so ur post confused me a little bit. Let me just iterate what I plan on doing: I have sanded, brushed, and ground the surface primer and rust away. I will ospho the surfsce, let it dry, reactive with more ospho, rinse, wire wheel/sand the area, do another coat of ospho, let it dry, reactive with more ospho, and rinse it off. At this point I will epoxy primer with my white spi epoxy. Do you guys think that's a dolid, rust - preventative plan? I plan on the final surface just being the white epoxy. I will probably seal it with the reduced epoxy too. When I get to painting and learning all that stuff I'm sure I'll be posting here a lot. Bits of the underside of the roof skin may show thru the inner roof structure since I'm not positive I'll had a headliner in the car. I'll have a cage, and guy say you can get a headliner in and out with a cage, but I'm not sure I believe that. Point being, I want it to look finished and nice in case it shows.

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#36 ·
Me again. I have a couple questions now that you have your rust treatment decided.

Will you apply this process to the remaining hidden areas of the body and bolt-on panels?

Are you including your labor in the $100,000 estimate? If so, at what rate?
 
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