Cracked windshields are not only illegal in most states, but are not safe on the road. Damaged windshields also let in moisture which, according to Auto Media, causes corrosive rust to form on steel surfaces and to compromise the adhesive bond of the windshield glass. To replace a windshield on a 1978 Ford vehicle, you will need a few tools, a powerful bonding agent and an assistant to help guide you. Contact your local Ford manufacturer to order replacement glass that fits your '78 model.
Wear safety glasses and utility gloves to protect yourself against hazardous glass.2
Dismount the rearview mirror. With a small Phillips screwdriver, remove the screws that secure it to the glass. Slide a small flathead screwdriver underneath the mirror's base and begin to pry upwards. If the adhesive is too strong, slide a thin razor blade underneath the base so that it will cut at the adhesive. Set the mirror aside once you have removed it.3
Use a trim removal tool to remove the car's top trim piece that lines the outside of the windshield. Insert the hook of the tool inside the gap between the base of the windshield and its weatherstripping. The hook must reach all the way inside the trim until it stops at the trim clip. Once the hook reaches inside the clip, pull upwards on the clip so that it will loosen the trim. Once the trim is loosened, you can remove it manually.4
Use a carpet knife to cut the window's inside molding from the outside of the Ford. Make the cut smooth, slicing around the perimeter at a steady pace.5
From inside the vehicle, push on the glass with both hands to dislodge the windshield from its frame. Have an assistant catch the glass from the outside of the car so that it will not fall and break.6
Use mild soap and a rag to clean away the sticky adhesive buildup from inside of the frame before replacing the windshield.7
Apply a bead of urethane caulk on the inside of the window frame. With your assistant, set the glass in the bottom of the frame first, and then lift the upper portion of the glass up and inside the frame. Press your body weight on the glass so that it creates an airtight seal.8
Allow the urethane caulk to set for 24 to 48 hours. Remount the rearview mirror with a mirror adhesive, which you can buy from an auto parts store. Follow the remounting process as directed on the product label.