Park your car in an area where the windshield will be in direct contact with full sunlight for at least three hours. This will heat the exterior of the glass and begin to soften the adhesive that holds the mirror bracket mount.
Hold a portable hair dryer about 16 inches away from the interior side of the windshield. Turn on the dryer, and wave a steady stream of warm air back and forth over the mounting bracket and the surrounding glass to heat it evenly. The inside of the glass should be nearly as hot as the outside to avoid cracking the windshield during removal.
Cut around the circumference of the base of the mounting bracket in short, slicing motions with the razor blade. You are trying to separate the softened glue from the glass. Stop when you have created a deep, circular groove between the glass and the mounting bracket.
Heat the glass and the mount with the dryer again, aiming the flow of heat at the base of the mount where the razor blade was used. Use the same back and forth motion when heating the glass.
Use a crescent wrench to grasp the mounting bracket and twist it off with a rotating motion. The unit should come off easily. Moisten any remaining traces of glue appearing on the windshield with a cloth soaked in alcohol to make them less likely to reattach as the glass cools. Remove the last fragments of glue with the razor blade to clean the glass.
Read more: How to Remove Rear View Mirror Mount | eHow.com How to Remove Rear View Mirror Mount | eHow.com