Yup. I did. And two years and 4000 miles later, it's still holding strong.

Most will bust your chops for even considering it, but it does work. However, it's supposed to be used for "non structural" components. Most of the Mustang's shell plays some structural role.

In convertibles, the cowl does little to nothing. The heavier rockers and floor reinforcements and torque boxes do all the work on them. But, on coupes and fastbacks, some load goes through the cowl to the A-pillars and into the roof.

So, I can't say how well it would work on a non-vert. It might do just fine. Prep is everything. The parts need to fit perfectly and the surfaces must be rough but clean. You'll also need LOTS of clamps to put it together.

As with most panel repairs, I used some screws for alignment and clamping. They can be located under the fender, etc. They help with the load-carrying, too. I did place a few tack welds here and there, too.

I completely agree with doing underdash work while the cowl is out. I did the same. But there's no reason to wait until after paint to do wiring. Do your underdash work (including heater installation, etc), then put your cowl on. Then get it painted.

Tip: Paint the lower cowl body color before putting the hat on. Also cut a piece of heavy plastic to protect that paint from overspray when they're painting the car. Extend a "tail" of this plastic down through the driver's side vent hole so that you can grab it and pull it out after paint. A few pieces of masking tape can be used to hold it in place.

 

Most will bust your chops for even considering it, but it does work. However, it's supposed to be used for "non structural" components. Most of the Mustang's shell plays some structural role.

In convertibles, the cowl does little to nothing. The heavier rockers and floor reinforcements and torque boxes do all the work on them. But, on coupes and fastbacks, some load goes through the cowl to the A-pillars and into the roof.

Well, you're right, and wrong. Most of the Mustang is structural, because there is no frame. However, the cowl is not decorative, it is a huge torque box that joins the A pillars, and thereby each side assembly, together. Unless you were willing to underwrite some liability for possible failure, I'd weld it as it was designed. Modern cars are often designed to be glued together, but the Mustang was not.

 

Crash, thanks man! Great info. I know the traditionalist won't like the idea, but it seems as if the adhesives are very strong and some even can be used in structural areas.

Are you the Crash on dfwstangs that does the pinstriping?

I am in Dallas. One reason I want to do the wiring after paint is that we have put a 2JZ into this 65 coupe and will have the motor with harness out of the car for painting the engine bay, and the way we have the ECU mounted under the dash is way easier to get to with the cowl out. Not doing the heating, etc right now, will add that in later, probably vintage or classic air setup

 

I wouldn't hesitate in using the available panel bonding adhesives for this job. I've always used 3M 8115 and it is stronger than the surrounding sheetmetal.

 

My body man keeps pushing me to do it with the cowl top. I still may just do it.
He keeps saying the adhesives he uses are stronger then welds when he has seen vehicles he has done come back for other wrecks and the parts he glued held up stronger then the welds around them. Food for thought.
My paint supply house also said the same thing, and people have used it with success. The only nay sayers will probably be the old school and or uneducated guys on the subject that think the old way is best.
Lynn

 

I have even thought about doing a combo of both. May be glue the area under the windshield and a few other areas and do a few spots welds on the corners and middle sides and on the long stretch under the hood.
Lynn

 

Thanks Everyone.

I did find this test. Panel bonding adhesive, vs. bolts, vs. welds.

Welding or Bolting vs gluing panels on, a science project...

 

The question is: Are you comfortable driving around in an experiment? If you are, go for it.

 

I wouldn't be afraid to have... YOU try it!

There is a lot of surface area for bonding. And it was only spot welded to begin with. If you can get all the surface areas to lay flat enough to mate well, I wouldn't be a bit surprised if it held up fine.

 

It's going to be stronger than the surrounding metal (And spot welds). I see no reason not to do it.

 

I agree with johnny.
I saw a demo of the 3m stuff at a paint shop. The metal tore before the panel bond. D it. Plus you won't eff your paint with heat.

 

My concern would be more with "How's it holding up in 10, 20, 30+ years?"

 

Question: what happens when the next guy wants to take that bonded cowl apart? How does that work?

 

You never build it for the "next" guy. I always get a laugh when some one says this, you build it for you and what works for you to get the job done.
Lynn

 

Done correctly, the next guy won't have to take the cowl apart. The only reason to take it apart is rust.

One reason that manufacturers have gone to bonded structures is because the amount of surface area that is bonded is greater than a series of spot welds. This improves structural rigidity, joint strength, and lowers harmonics. Manufacturers such as Aston Martin and Audi completely bond their entire structures with no welds or fasteners. You could actually buy Dow 2096 from an Astin Martin or Audio collision dealership in ratchet gun cartridge form if you wanted. It's what they use for collision repair of structural components on a DB9 or A8 without welds. Sans that, the 3m stuff is easier to find. I used it on my race car to bond it's cowl, roof, and floor in.

 

I don't see a problem. OEM's are holding parts together that are stressed more than our cowls with such stuff. One thing I never liked about welding in stuff like cowls is that you have an amount of metal overlap, places difficult to rustproof that tend to accrue moisture. And if you try to protect such areas with a coating when you weld them most of that protection burns off. Even the "weld-thru" stuff. With adhesive you can epoxy paint and seal every thing as much as you like and final cowl assembly won't harm it. Plus the adhesive itself seals moisture completely out of the overlapped joints.
You could install floor pan patches with overlapping joints with adhesive and effect a solid but totally crappy repair. Such patches need to be butt-welded in for a quality repair, adhesive is entirely the wrong tool for such a job even though it would "work". But adhesive is about ideal for repairs like cowl replacement.
As for long term durability, people don't seem aware that this stuff wasn't invented for cars yesterday. It was handed down to us from the aerospace industry where they've been using it for years and the FAA is a little more picky about such things than the DOT. If you've flown a commercial flight in the last 20 years or so you've participated in the "long term testing" of such structural adhesive . Fairly new to us antique car folks, but Boeing started widely using related structual adhesives on 747's made back in the days of the Vietnam war. And some of those planes are still on flying duty.
Then again, if you choose to spot weld the cowl back in just exactly as the factory did then that's great too.
Almost didn't post this. Even though I mentioned twice about it being wrong I can imagine some ding dong with rotten floor pans with a lightbulb going on over his head. "Hey, even though I don't have a welder or any welding skills I can still patch my floors. Hey, maybe like everything on my car." People do enough damage with overenthusiatic use of Bondo and fiberglass already, picture idiots loose with epoxy. Eeek.

 

Eeesh, use a torch to loosen the adhesive. Most adhesives cure at room temperature but cure can be accelerated by temperatures up to 350 F or so. For removal, heat with a torch to around 700-900 F. Possible to do with a hardware store propane torch but a bigger torch works better. Body shops usually invest in induction heaters which allows them to debond plastic parts from steel and reuse the plastic (urethane/PVC/etc) when a torch would burn or melt it. Such heaters are also ideal for just separating steel from steel but exponentially more expensive than a torch.
So I guess the next objection would be that if you car catches on fire pretty badly that all the glued panels could potentially come unglued and detached. I'll cede that point. But if your car is burning bad enough to raise temperatures that high you can pretty much assume everything else in range of flame that hot is being ruined also.

 

Thanks, GypsyR. So it actually sounds like separating the bonded panels could end up being *easier* than drilling out all those spot welds if future access is required.

You have laid out some strong arguments for the bonding, and I appreciate the info. Would you help me understand why you think it would be a bad choice for floors?

 

I'm finding this "How's it going to hold up in 10 years" thing pretty laughable, actually.

I have things sitting here that were epoxied many many years ago, and they haven't turned to dust yet?

I'm willing to bet, (without proof of course), that the adhesives will be around far longer than the car will.

Edit: I'm going to go far out on a limb and say the adhesives are probably a BETTER choice than spot welding.

 

Many years ago air planes were constructed of dissimilar metals so they used a zillion rivets. Failure was often at cracks starting at the holes. They developed bonding which was better and longer lived. Space program high temp ceramics and other materials bonding was the only way. Of course now high perf aircraft uses carbon fiber and titanium parts bonded together. Modern grand prix/Indy cars are largly carbon fiber and titanium. Even modern racing bikes are largely carbon fiber.

IMO welding, especially spot welding is becomming obsolete like the buggy whip!


Slim

 

A lot of aircraft being produced today (Cessna, Piper, Beechcraft, Mooney, for instance) are still riveted. Some light planes have used bonding with varying success. The Grumman AA-5 series (Cheetah, Tiger) used a lot of bonding, and there were some problems with delamination along the way, and owners complain of expensive repairs, but I suspect the challenges of bonding aluminum sheets are different from bonding steel.

There are also many light planes with primary structure made of composites (foam and fiberglass, with a bit of strategic carbon fiber), Cirrus probably being the most well known production model, but there are many.

Then, of course, there are those of us who spend a lot of time cavorting about the sky inside steel frames covered with nylon fabric, with the 3'rd wheel in the back where it belongs... :shocked:

 

I was helping a friend replace the complete floor in a Chevy Nova II and the bodyshop owner across the street stopped by. He stopped us, ran across and got his Plexus gun, came back, and we bonded the complete floor into the chassis using 16 screws to hold it in place until the plexus set. 4 along each rocker and 4 front and back.

 

My problem with floor pan patch panels may be purely aesthetic. A properly welded in patch panel will be butt welded to existing solid pan. Ground down and finished ideally the finished repair will be undetectable. To do the same repair with adhesive you'd need to overlap the patch on to existing metal forming a flange. You could flange it to be about undetectable from under the car or under the carpet but not both. Patches that look obviously like patches I find ugly. Even if they are hidden from normal view, they're still there and scream "patch job".
I remember a demonstration some years back where they used adhesive to install a lower door corner patch. Worked great and looked great. Until you looked inside the door shell where it looked like a hobo's butt. With gobs of tar on it.
The difference is with the cowl replacement under discussion is that the parts are being replaced in a entirety. Like the factory did just using a different method of attachment. Replacement, not patchwork.
A skilled welder can repair/replace about any sheetmetal to look as original. Something patched with adhesive will always show as a repair one way or another. Something installed with adhesive just looks like someone did a good job of removing all welding marks and neatly applying seam sealer.

 

Notice design and method of manufacture go hand in hand. Imagine discussing the pros and cons of spot welding the sheet metal on a wood frame 20s GM car body VS screwing!

 

I was also thinking of bonding around the wheel well lip when I put the next quarter panel on. I hated welding and grinding down that lip on the full quarter I did.
Lynn

 

Interesting thought. I'm about to finalize the install of two 1/4s.

I haven't drilled the plug welds in the lip yet. How tight does the panel bond adhesive need the panels to be? Mine line up fairly well but need to be clamped pretty hard to actually touch.

 

I would only weld the cowl in. It is true a lot of the new cars that we work on have some parts that are bonded on. But keep in mind these new cars were designed that way, I think even if they had the technology back then it still would have been welded in.

 

I'm sure if they had the technology back then and if it saved them money on the car doing it, they would have bonded it on and then some.

Adhesives weren't even used much back then, the pins used to attach all the emblems and metal staples used about on the car to hold weather proofing and such is proof of that.
Lynn