No matter how careful you are when driving and working around your car there's always that stray rock or debris that can ruin your glass, and your day. No matter how your glass gets damaged, repair is not a tough job to perform in your own garage and requires only a little assistance from a second person. Good, original glass is hard to find, but if you're not worried about factory date-coded glass you can buy new pieces. We had a long-standing crack in our window and a scratched back glass from some old bodywork done by a careless body shop, and decided it was time to call Classic Industries and replace the damaged glass in our daily driver.
Windows are installed using two basic methods: butyl tape or polyurethane.
Polyurethane is a rubber-like adhesive that is squeezed out of a tube loaded in a caulking gun. It's the method used on newer cars. Newer auto glass has the dark-colored band of enamel baked into the glass referred to as a "frit." The frit gives the polyurethane adhesive a surface to bond to, which is critical. Old glass doesn't have a frit band for polyurethane to adhere to so you're stuck trying to bond to a smooth surface, which isn't great for a lasting installation. A previous windshield installation on our project car was done with polyurethane, and within a year of hard driving, the glass had broken its bond to the adhesive around 80 percent of the perimeter and was causing major water leaks. Some critics will say the installer must not have cleaned the glass before installing it, but I watched the initial installation so I know it was cleaned properly. There's no way to control the polyurethane and make a clean install. You simply glob it on the window channel and press the glass onto the adhesive and it squishes out like ketchup on a good burger. The messy and ugly adhesive can be seen through the glass after the installation is finished. The frit on new glass hides the messy polyurethane.
A glass installer in California told us that he can't legally use anything other than the polyurethane. If you want to install your window in an ultra-clean way and use the factory installation method, you're probably stuck doing it yourself. The benefit of doing it on your own is that you can address any rust issues and repaint the area.
Don't forget to wear your safety glasses before cutting or lifting out the glass. Also realize there can be sharp edges present and you can get cut, especially if you're working with broken glass. It's a good idea to wear some heavy-duty leather gloves when doing the install.
Most auto glass installers don't care about the quality of their work located behind the trim. To remove your glass, they use a 90-degree razor knife with a handle. While cutting out the glass, their knife cuts into the window channel and chips the paint and leaves a hidden place for rust to start breeding. Our old Camaros have problems with rust around the windows without the help of somebody else, so we operate under the premise that if you want something done right, you have to do it yourself. There's a product called pinch weld primer, which is a heavy-duty sealant and bond promoter that you brush on a scratched window channel to protect from rust and increase adhesion.
Window trim warning
Before laying one finger on your window trim, you should know that original trim is fairly strong but reproduction trim is very flimsy, and it bends easily. If you have reproduction trim you're going to have to be careful removing it because it dents if you even stare at it too hard. If I didn't know better, I'd think it was made of thick tin foil. Original trim is much more forgiving, and it fits better.