Hi Andy, I replaced the original antenna on my '39 CS 15 years ago so my memory is a bit faded but, the open & closed cars antenna's are the same but different. As I recall, there is a spring mechanism in the base where the antenna pivots and locks in the up or down position. That "spring" applies pressure which keeps the antenna locked in either position. When down, the antenna should rest against the plastic clip on the windshield divider. As I recall, there is n adjustment for tension on the antenna. Sorry for the long winded explanation without providing a surefire solution. If all else fails, take a hammer to it.
