[sick472]

I'm going to say the bracket closest to the pull knob needs to be closer to the vent door. Maybe it's been screwed down in the wrong place.

OR, I'm not familiar with that style of pull knob. Is the forward tip of the knob supposed to stop at the bracket (like shown in your pic) or "pop" up and over the curved portion of the bracket? Can the knob be rotated back so that the leading edge can push past the curve in the bracket?