Sticking seat belt help needed

I had the same issue with the 75 shoulder belts I got for my 73. From what I remember you have to loosen the collar screw ( silver band ). It should be just loose enough to allow the plastic inner to move freely but have enough friction to kick in when the belt is yanked. Mine still lock up if it' really cold out and I'm in a hurry, but I KNOW that they will still work in the even of an impact
To get an idea of what the mechanism is doing, pull the belt really slow to see what kicks the stopper in.