You probably have to clone objects before you change some stuff. Be creative. You have one Object 'Car'. Clone it. You have 2 Objects 'Car'. On the one car you delete all polygons that belong to the door. On the other car you delete all polygons around the door. Now you have 2 objects: One car without door. And one stand-alone door. Now You can turn and move the object door how you like. With the hauler it is nearly the same.
This thread is not for asking questions about the basic use of 3dmax. This thread is for posting finished scenes.