Hi jfritsch. You're the second person to ask this question this week, so there must be something unusual about it. Most mirrors have an obvious screw in front. Instead, look for a small plastic tab that you must press. If the trim cover looks like it could be slid up the arm, there might be a set screw hidden under it. If you're replacing the windshield and aren't worried about the mounting button breaking off, you can try tapping upward lightly on it.
If this helps, holler back with what you found. If it still doesn't come off, you might have to ask at the dealer or a winshield shop.
Saturday, March 20th, 2010 AT 6:46 PM