Follow thru as to what that plastic arm should to when the plunger moves it. If I remember it turns something to make it open. Also see if the plunger is coming out far enough to move the plastic arm the correct amount. Had mine apart several times and it works OK now but I still have to pull it back out to set the change the lock tumblers so they match the door key. My lock came from a wreck and of course it wasn't set for the same key my door is. Jerry