Cowl Vent keeps falling

[Chappy]

I have a 48 sedan, when I got the car, there was a cotter pin going through the middle pivot. I replace that with a 1/4" bolt and nylock nut with slight tension on the bolt. Also the one rod was not connected to the back of the radio, so I connected that as well. But while driving it still falls. I read a few other threads about different model years that there is a spring, mine does not have one, is there supposed to be one?