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.
Windshield and backlight installations...
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...
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.
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...
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...
2: The windshield's base molding is installed to provide a solid foundation for glass installation.
3: Antique Auto Glass begins...
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.
4: Using a soft plastic homemade...
4: Using a soft plastic homemade tool, Frank Dohs pops the rubber gasket lip over the windshield, beginning at the bottom. Instead of using a rope to pop the rubber lip inside the body, Frank pops the outer lip instead, using the plastic tool to get there. The inner lip is already inside.
5: Frank firmly presses the...
5: Frank firmly presses the windshield in place, which seats the glass and squeezes sealer around the edges. He suggests firm pressure, but not too much.
6: With the glass firmly...
6: With the glass firmly pressed in place, Frank runs a bead of sealer around the perimeter between the glass and rubber gasket. Lacquer thinner and a razor blade are used to clean off the excess sealer.
7: Sealer is applied between...
7: Sealer is applied between the rubber gasket and body as shown. This ensures water won't leak between the rubber and body. This is the vintage Mustang's most common leak area.
8: The sealer between the...
8: The sealer between the rubber gasket and body is spread to fill out the space and keep water out. Sometimes, the molding will breach this seal, causing leakage. If this happens, you have to remove the molding and seal again.
Closing The Gap Mustang windshields...
Closing The Gap
Mustang windshields leak mostly in the upper corners because installers frequently fail to fill the huge voids with sealer. Water tends to collect there, finding its way down the A-pillar to the dashboard and kick-panel area. This area must be filled with sealer and properly spread in all directions before the molding is installed. Water needs to be channeled away from this area, down the outside of the A-pillar to the bottom where it safely passes away from the interior. When it does, your feet stay dry.
Be Careful Out There We often...
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.
1: Antique Auto Glass installs...
1: Antique Auto Glass installs backlights the same way as windshields, with the rubber gasket going in first. Plenty of sealer is used between the gasket and body, and the glass and gasket. The base molding is then installed. The glass is seated in the base of the gasket first.
2: The rubber gasket's lip...
2: The rubber gasket's lip is popped over the outside of the glass as shown. This is a cleaner approach to glass installation. When rope is used, as Ford suggests, windshield sealer gets all over the place.
3: The rubber-gasket lip...
3: The rubber-gasket lip is popped around the glass perimeter as shown.
4: Inside, the rubber gasket...
4: Inside, the rubber gasket needs help. We pop the lip around the edges while someone presses from the outside. This way, everything seats into place.
5: Sealer is added between...
5: Sealer is added between the glass and rubber gasket once the glass is seated.
6: Sealer is then applied...
6: Sealer is then applied between the rubber gasket and body to keep water away from the interior.