you have to loosen the lock nut and then turn in 1/4 turn increments as previously stated, as far as it turning its self, your lock nut may be worn out or loose, if it isnt then i would look into a replacement...but now the main question is this....."is it manual or power steering?"...if it is manual then you should be able to set it fairly easily, i had no problems with my 73, if it is power steering, i would take it to the dealership and have them adjust it...that way if they cause it to lock up they have the repair there work or pay for any damages done to your truck in the worst case cenario that you do get involved in an accident because of there services.....power steering i would say if you want to try it your self, i would try 1/16 inch increments it would take a lil longer but better to take your time with power assist steering boxes...lol..i have a repair manuel for the dent sides that has a segment in it on addjusting the steering box if you need it i can post it for you...