Factory auto glass installation has changed a lot since the mid-1960s. On today's new cars, windshields, backlights, and side glass are glued in for two reasons—safety and ease of factory assembly and aftermarket replacement. Glued-in glass won't pop out in a crash. It is also easier to remove and replace. Classic Mustangs have rubber gasket windshields and backlights. Rubber gasket glass tends to pop out in a collision. It is also labor intensive to service. The greatest problem with rubber gasket windshields and backlights is leakage. Poor installation and deteriorated rubber both contribute to the problem.
Rubber gasket glass leaks due to irregularities in glass, body, and gasket along with improper installation. And sometimes you can do all the right things and it will still leak. We looked to Terry Simpson and Richard Bramlett at The Restomod Shop in Stockton, California, for advice on how to properly install windshields and backlights. They took us through the process on the toughest install—a '65 fastback.