One of the more frustrating aspects of vintage Mustang ownership and restoration is leaking windshields. It's frustrating because no one wants to see their carpet-or feet-soaking wet. Classic Mustangs used rubber gaskets for windshields and rear glass through 1968. Beginning in 1969, Ford started gluing in the windshields, yet stayed with rubber-gasket backlights through 1973. Glued-in windshields have been a blessing because, unless you're really careless, they will not leak. Rubber-gasket installations take a lot of practice to keep them from leaking. Rare is the rubber-gasket windshield that doesn't. If your toes and carpet are wet, you're in good company because a lot of us wrestle with the same problem.
We're going to explain how classic Mustang windshields and backlights are installed, and how to prevent them from leaking. Because this is an inexact science, we offer no guarantees. Sometimes, you can painstakingly install a windshield, thinking you've covered all the bases, and still wind up with water on your floor or in your trunk. We hope this useful information will lead you to a dry interior.
Neatly And Cleanly
Windshield and backlight installations must always begin with clean surfaces. Both the glass and body must be pristine and clean. When cleaning the goop and poop off the body, take extra care not to damage the paint. Scratching the paint down to the primer and bare steel leads to corrosion and rust-out. | 
Windshield installation should begin with clean surfaces and new molding clips. Always apply windshield sealer between the clip and body to ensure proper sealing. Water tends to sneak around the clips because they provide an air gap. By using a sealer between the clip and body, the air gap is eliminated. | |
Unconventional Method
We invited Antique Auto Glass to visit our shop and install a windshield. These guys use a different approach than the Ford shop manual instructions, which tell us to run sealer around the inside pocket of the gasket as well as the outside pocket, then install the gasket on the windshield. Antique Auto Glass follows the Ford shop manual's instructions to apply sealer to both pockets before installation. Then, they install the rubber gasket on the body first. Once the gasket is installed on the body, they follow with the windshield. Instead of using the rope trick we've all been taught, Antique Auto Glass' Frank Doha lays the glass on the rubber and works the rubber over the glass with a tool.
1: Installation begins with the rubber gasket. Sealer is applied to the inner and outer pockets as well as the body to ensure proper sealing all around. The gasket is installed next. | 
2: The windshield's base molding is installed to provide a solid foundation for glass installation. | 
3: Antique Auto Glass begins glass installation at the bottom by setting the glass in the gasket pocket. The glass is laid back against the rubber gasket. |