I have a 2011 FLTRUSE. The left lower vent keeps closing on me. I found a little nut under the glove box liner that attaches to the 'twist knob'. I tried tightening that but it seems to have had no effect. This only happens on the left side -- ride side seems to stay put. Is there any adjustment short of jamming something inbetween the sliding vent and the glove box itself?
The nut is the only adjustment, and you need to be very careful when tightening it. The stud it attaches to is actually a carriage bolt with a smooth head that you can't grip, and it's only held by the plastic of the vent. Very, very easy to strip out and then be unable to remove the nut.
I'd suggest that your first course of action should be to take it to the dealer and get it documented and let them be the ones to try to fix it and screw it up. They screw it up, they get to pay to fix it. You screw it up, you get to pay to fix it.
I'm attaching a drawing that will show how the whole thing goes together, but basically there is a toothed plastic piece that is spring loaded and it should hold the vent in position. In reality, a lot of them don't work as designed for various reasons. A better design would fix it, but that would make too much sense.
Jerry