To replace a car's back window glass, also called a rear windshield, begin by removing the existing glass using a windshield knife or windshield wire and grips. Use silicone lubricant to moisten any weatherstripping that holds the glass into place. Know that rear windshields installed with adhesive often break, so you may have to remove the glass in pieces.
To install a glass windshield with adhesive, clean the edges that hold the windshield in place to remove any old adhesive or other debris that could prevent the adhesive from adhering fully. Ensure the new windshield is a perfect fit by sliding it into place. Remove the new windshield, then place a bead of windshield adhesive around the opening where the old adhesive once was. Lower the new windshield carefully into place, allowing space for any trim that fits between the glass and the metal car opening. Let the area dry, and install any trim.
To install a glass windshield surrounded by weatherstripping, apply the weatherstripping around the edge of the new windshield, and insert a nylon cord into the other channel on the weatherstripping. Ensure that the ends of the nylon cord are long enough to grip easily and that the ends stop at a corner. Coat the weatherstripping liberally with a silicone lubricant. Put the windshield into place.
Slowly push the weatherstripping into the channel around the car rear windshield opening while carefully removing the nylon cord. Work with a couple of inches at a time, using a helper in the car to support the glass if necessary. Continue until all of the weatherstripping is completely inserted.