Jim Smart
May 24, 2007

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.

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.

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Be Careful Out There
We often see mistakes made in windshield-molding installation. Windshield shops sometimes use mallets to install the stainless molding, a procedure that can chip paint and dent moldings. Frank suggests firm pressure on the molding using the heels of your hands. The objective is to pop the molding under the clip. You don't need a mallet, just firm pressure with your hand.

Mustang body leaks aren't always rooted in the windshield and backlight. Cowl vents are the reason for leakage more times than windshields. Check your Mustang's cowl-vent dams for rust-through. Cracks in the lead seams at the roofline and A-pillars can cause a water leak. The same can be said for lead seams at the sail pillars and trunk area. Examine your Mustang's body thoroughly for leak sources. There are many, including rubber grommets around wiring harnesses, accelerator pedals, brake lines, and antenna leads. The rubber seal between the trunk lid and body will leak if exposed to substantial amounts of water. Quarter-panel end caps, taillights, side markers, and even trim pieces can be leak sources. Check them out.

Classic Mustang rear windows install the same way as windshields. Probably the most unforgiving rear window, also known as the backlight, is in the fastback. It leaks because it lies so flat, which makes it easy for moisture to collect around the perimeter and leak inside. That's why lots of sealer is needed around the fastback's rear window, especially around the outside between the rubber and body. Molding installation follows the same protocol: with a firm, soft hand.