How do I un-jam my seat belts? Help!

Passive restraint, The spool lock is supposed to be inertia reaction. So long is spool rotates at a low speed the lock does nothing. In a accident the spool would start to rate very fast with passenger movement. Spool lock activates. I'm sure you have noticed that you have beeter luck pulling the belt out very slowly. Of course the spool does rate faster as the belt lap diameter gets smaller
Anyway... pull the retracter, play with it and see how it works. Plus you will see it is loaded with hair, dust, lint, etc... The belt carries a lot of stuff to them. All I ever needed to do to those in our 73 Valiant and 87 Gran Fury, is thoroughly clean them. Only 1, right rear of the Valiant, still had a little attitude after reinstall.