1972 Pinto back right tire spins with a wobble?

Hello I have a 1972 Ford Pinto, and the tire spins awkward, when driving the car I didnt feel any effects but when you see the tire it seems like is going to fall out, this caused me to loose one of my hub caps, Any sugestions to what might be the problem, I rotated the tires so its not a bent rim or the tire. Any help will be apritiated thanks