What can cause the right rear wheel to wobble on a 1987 Chevy Caprice if the wheel itself is straight and balanced?

sounds like a bad wheel bearing.

you could aslo have a loose lug nut or one of them have been stripped happened on my friend's 87 caprice

could also be a bent axle shaft.

Answer

id go to a junk yard and get a used one off another Chevy i had a cutlass did

that nd sure enough tire came off along with the shaft....something to think about huh?