back brake grabbing

I have a 1990 olds cutlass ciera, and the back brake is grabbing and locks up when stopping. No air in brake lines. Took the rear drum off and the brake shoes, drum and assembly look ok. With very little force on the brake pedal the rear passenger drum will lock up. Any ideas??

could be a problem with the drivers rear brake. If its frozen up it would put all the pressure on the other wheel. It worth a look.