1977 Other Chevrolet Models Door locks

Interior problem
1977 Other Chevrolet Models

The passenger side door lock will not unlock from the outside, it's like the key can't turn far enough to unlock the door. Then on the drivers side u can use the key to get in BUT you have to open the door and then remove the key because when u turn the key back far enough to remove the key it relocks the door. I've changed the actual locks but no change so i'm assuming it's in the linkage, help!