Windshield install... sealant or no?

been away for a long while, project is stalled the way projects go sometimes, but moving forward now. Windshield was installed dry with new gasket after painting... I think I need to go back around with sealer around the gasket inner and outer channels to seal it up properly, right?

I fear the trim around the windshield on my convertible is gonna kick my ass too, but not there yet. if anyone has any tips for that I would be all ears...

Why was it installed without the normal "goop"(technical term)? A sure way to get leaks. I suggest pulling it out and doing it right but if you are not willing then by all means use sealant on the outside edge between the seal and the metal. Be VERY liberal. The metal the seal is resting on is not flat at all and anything that gets by that outer sealant will leak into the car. Use a urethane sealer like used in modern installations between the seal and the glass.

Dry is bad. Re-do

Also make sure that you an extra large dollop of sealant around each of the trim clips that hold the stainless trim around the windshield. The slight spring tension crated when the trim is installed is enough to lift the clip and allow water in behind the clip and then you have a leak.

Butyl caulk (3M Bedding and Glazing Compound) is what you need on all pre-69 windshields

As far as I know butyl rubber (tape) and Bedding and Glazing compound (caulk in a tube) are two completely different things. I would NOT use urethane sealant in a rubber gasketed windshield. I once contacted 3M's tech support online and they allowed as how you could use urethane but really recommended to use the bedding and glazing compound just like Ford said to do. To seal it correctly you would put a thin bead of sealant inside the rubber and put it on the glass. Then a bead inside the rubber again on the other channel and install the whole thing. Although folks have pulled up the rubber and "injected" sealant in there after installation to try and resolve a leak, I don't think you'll have success sealing the entire windshield that way.
When I put a windshield in without sealant, it leaks. My '67 is that way now. Basically because I need to store the windshield somewhere anyway and it only takes me five minutes to pull or install it with no sealant or trim in place. The car doesn't go outdoors though.
So the correct way (according to the people that made the car and the people who made the sealant) would be to pull and replace the entire glass. Sorry. On the bright side, I've pulled and replaced my front and rear glasses several times and the rubber seems to be holding up fine. So odds are yours will be OK too. If/when I get to the point of installing my glass permanently I plan to buy new rubber whether I seem to need it or not.

As to using urethane to seal the front edge of the gasket to the glass like virtually all modern glass installations...


If it's the way one of the best mustang builders in the country does it, it's good enough for me! I can tell you it makes for a very clean install as well. The urethane adheres very well to the rubber.

He makes that look TOO easy!!

Horseplay said:

As to using urethane to seal the front edge of the gasket to the glass like virtually all modern glass installations...

If it's the way one of the best mustang builders in the country does it, it's good enough for me! I can tell you it makes for a very clean install as well. The urethane adheres very well to the rubber.

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The Youtube video you linked to is part 2. If you look at Part 1,
you will see that the "best Mustang Builders in the Country" use the 3M product I referenced to seal the gasket to the pinchweld. Though he uses urethane to seal the glass to the gasket, there are professional differences of opinion on the use of urethane for a vintage Mustang windshield. Remember that modern windshields are actual structural members of the car and the urethane is an adhesive. On the old Mustangs, the windshields floated in the opening and were not structural members so they need to be sealed from leaks and that is why the factory used the glazing compound as sealant when they installed windshields on the assembly line. The glazing compound has been referred to as liquid butyl. When I referred to it as butyl caulk I was not referring to butyl tape or rope caulk though I see from a CJ Pony youtube that the rope caulk is their sealer of choice for the old Mustangs.

Not sure if you thought I was disputing your advice but if you check my first post here I too advised to use "the goop", as I so technically put it, between the gasket and pinch weld. The urethane reserved for gasket to glass. Flex between the glass and gasket is not required and I would argue even potentially detrimental. The gasket can absorb all the necessary movement to flex with the car body in itself.
As I have referenced here on the Fix a number of times over the years, I have an advantage over many at times in that the company for which I work is a leader in many areas, one being adhesive structures. I happen to be friends with a number of chemical engineers and such on staff and often consult them on projects. It was with their blessing I proceeded to use urethane for my windshield installation just as I advised in this thread. When it comes to professionals, trust the guys who make the stuff to know where it can/cannot perform more so than the guys who use it. Simply because they know WHY it works.

msell66 said:

Dry is bad. Re-do

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That's what she said.

3175375 said:

That's what she said.

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Well, dry it is if I get to do a re-do.

"When it comes to professionals, trust the guys who make the stuff to know" To be sure. That's why I contacted 3M directly. Anybody else can too, they're quite nice.