If a crack is longer than three inches, or if a chip is larger than a standard coin, the structural bond of those laminated layers is likely broken beyond repair. Furthermore, where the damage is located is a huge deal. If a crack reaches the very edge of the glass, it has compromised the "seal" that holds the unit to the car's frame. In cases like that, the normal vibrations from the road will eventually cause that crack to spread across the entire surface, making a full installation unavoidable for your safety. auto glass replacement