Roof repair vs Replacement

[scotts74birds]

I dont think I posted this on FBBO before, if I did, I'm sorry. But it is finally time to start this job. The car is a 74 Roadrunner w/ sunroof. It had a flop into a ditch by the PO and there is roof damage. The car is going to the shop next week only to get checked out to insure the car is straight before i start. It only appears to be sheetmetal and some tweaked braces. Doors shut square, glass isnt cracked, none of the pillers appear tweaked. I have a spare roof for it, but am unsure on whether to strip it, replace the roof braces and re-skin it with the new roof. Or an entire replacement. If the popular opinion is replacement, then I'll need advice on how to reinforce the unibody during removal. I've seen some of the talent and knowledge of the members here and I think I'm in good hands. Thanks for any advice, Scotty

 

[Donny]

You can unskin the roof, but, it's a lot of work, and about 200 spot welds to cut thru. Check my thread called Donny's 1969 GTX, there are pics there on this subject, good luck!

 

[69HEMICORONETR/TCONV]

I have done both, Repair/Reskin and Replaced, .....I would ONLY Replace if absolutely necessary,... A Reskin is a LOT more work, You get to eliminate the alignment issues and save some stress and headaches, but the Finished product is much nicer and that's what it's all about. Reskin if you have NO structural damage and can get by with it.

 

[scotts74birds]

As I said, the pillars are good and straight, front and rear. The 200 spot welds to remove sound daunting, but doable. Guess i could de-skin the roof, [btw, its a sunroof car] and remove and replace one brace at a time to keep it square. The roof braces, front, middles and rear, have bends and tweaks to them. But nothing that seems to have affected "square". I'll try to post good pics this weekend so you pros can give me a true opinion.

 

[Donny]

The roof skin is NOT attached at all to the roof braces.

 

[scotts74birds]

Understood, the braces just have a bead of adhesive on them.

 

[Donny]

Actually, most everything I am doing on my GTX is far beyond what I've ever done before, and likely will not do again unless I get another hair up my yahoo. The roof skin will just slide off when all the spot welds are cut out. Get about 6 spot weld cutting bits, spray can of cutting fluid, and go to work! Be careful when you take the roof skin off that you don't 'torque' it as it's a big piece. My suggestion, get a friend to help you take it off, it will stand up nicely on the rear section.

Here's a pic or two of mine;

[/IMG]

[/IMG]

[/IMG]

[/IMG]

 

[scotts74birds]

Thanks Donny. I anticipate mine will look just like yours in a few days. So I guess I should also de-skin my extra roof and separate the new braces and ribs for use on the car if needed? Replacing them one at a time should keep me square, right? BTW, it appears you are pilot drilling the holes first. I've started with a spring-loaded center punch and a Blair cutter. Goes through both sides too easy sometimes, dont it! I have a cheap gas mig set-up. Any advice on wire size and type?

 

[Donny]

The bit I use requires a 7/64 pilot hole to be drilled first, get about 10+ bits, you'll need 'em, I hate dull bits! You need to watch penetrating the other side, or you'll have nothing to back up your welds...it's inevitable, you will but thru some of them, but be careful.

When you say cheap Mig set up, don't know what you have, and right off hand I can't recall the wire size I'm using, but it's a standard size wire, I have an gas cylinder, and I don't have a cheap welding unit, mine was about 1300 bucks -- if you're going to use this welding machine more than this one time around, I'd buy a good machine, this way you have something to grow into vs. disposing of after a few months of use.

It's all a balance, if you want to do your own work, you better have adequate tools, and time to do this work. Also, you gotta have cash to buy this stuff. Some shops will take this kind of work on for about $65.00 per hour, at least here in San Antonio I know of a few that would tackle this job for you...something to consider if you're a one-timer. However, there is much joy and satisfaction in doing it yourself, as I get from my labors...but at times I feel I am getting nowhere due to the thing called 'got to make money'!

Again, good luck!

 

[RGAZ]

Thanks Donny. I anticipate mine will look just like yours in a few days. So I guess I should also de-skin my extra roof and separate the new braces and ribs for use on the car if needed? Replacing them one at a time should keep me square, right? BTW, it appears you are pilot drilling the holes first. I've started with a spring-loaded center punch and a Blair cutter. Goes through both sides too easy sometimes, dont it! I have a cheap gas mig set-up. Any advice on wire size and type?

I recommend a 0.030" wire with gas shield. I use an argon/Co2 mix, but local shop can tell you what they can do.

Trick for drill-through: Find/get a nice size piece of copper and a bucket of water. I have a 1/4" thick by 3" piece of solid copper I use to backup my welds and with a nice clamp the holes fills up easy as pie. Drop in the bucket between welds to cool it. Where did I get the copper? I work in an electrical plant and we have copper bus scrap all over the place. I just bought some off our recycler.

Good luck,
Randy

BTW-My car has tree damage and I am considering changing the skin too. If I can tweak it back in with the body hammer I will, but i want to see who your comes out.

 

[66_B_Body4ever]

The gauge of steel you are welding is 22 thou, you should use .023 AWS ER70s-6 wire. The copper trick that RGAZ mentioned works pretty good and C-25 gas as he mentioned as well. Don't forget the weld thru primer!

 

[Donny]

On this weld-thru primer, how does it work? I've never used it, but I should!

 

[scotts74birds]

UPDATE..........Still drilling.

 

[66_B_Body4ever]

On this weld-thru primer, how does it work? I've never used it, but I should!

It's a zinc rich primer (cold galvanizing) that is applied only in the pinch weld seams over bare steel that aids in corrosion protection. It does incresase the difficulty level of welding a little, and generally requires a slight increase in the heat (voltage) setting to compensate for the zinc. Of note, that is the only real purpose for Weld thru primers, they have a low adhesive factor, and should never be top coated over as well.

BTW, we should always use this material no matter how much of a pain it can be...their is a variation on the material that uses copper instead of zinc which is easier to weld through, but it is not a sacrificial metal and doesn't provide the same anti-corrosion characteristics that the weld thru will. If you have a lot of welding to do, invest in a P-100 fume respirator while working with these materials...your throat and lungs will thank you and extend your beer drinking days considerably...

 

[66_B_Body4ever]

On this weld-thru primer, how does it work? I've never used it, but I should!

Here's a pic showing where I will use the copper based material, these seams will be completely sealed up so the copper based stuff works here...I will use the zinc based material in the seams on my floor pans to the frame rails that will not be sealed and more exposed to the weather, heaven forbid precious see's a wet day...lol

 

[scotts74birds]

Ok, working my way around the A pillars. How will I replace the leadded joint? I heard body filler will always crack in these joints.

 

[Donny]

Thanks. I'm going to get some of that zinc stuff then! I do have lots of welding to do; floors, rear frame, inner and outer wheelhouses, qtrs, trunk extensions...etc.

 

[66_B_Body4ever]

Ok, working my way around the A pillars. How will I replace the leadded joint? I heard body filler will always crack in these joints.

Well, the first option is to re-lead them, not an easy task these days as lead is a banned substance and a huge health issue, be careful removing the old material! Secondly, you may spray a good coat of epoxy over the prepared seam, allow to cure, scuff with 80-100 grit sandpaper, then apply a coat of fibreglass reinforced body filler. This material will not be as likely to crack and actually has more strength than the lead...the lead solder however will actually suck into the joint through capillary action to aid in strength...like an adhesive.
Third, you must thoroughly clean up the old solder and weld the joints in solid, which is my choice but not a factory style method...but then again neither is a plug weld vs. a spot weld.

Other choices could be adhesive bonding, but...I have seen the bonded seams reappear as a ghost line down the road. Very strong, best corrosion protection but not great in a high visibility area such as a sail/windshield pillar.

Of course there is oxy acetylene brazing...but not a path I would go down. MIG Brazing is an option, cooler than steel welding and now recommended by many manufacturers in place of steel MIG, but, you need 100% Argon sheilding gas and of course the wire...

Hope this helps...Jeff

 

[66_B_Body4ever]

Thanks. I'm going to get some of that zinc stuff then! I do have lots of welding to do; floors, rear frame, inner and outer wheelhouses, qtrs, trunk extensions...etc.

I prefer 3M's weld thru primer although there are many other good quality brands. Make sure you shake the material thoroughly before use...I mean shake it for another 30 seconds after you tire of the initial shaking and everytime you pickup the can...the zinc settles rapidly! Practice welding thru the material before you attempt your welds on your baby...One good medium wet coat is all that is required...just for coverage.

 

[66_B_Body4ever]

Hey Donny, Scotts74...hows the projects going?