97 Mitsubishi Diamante Rear Brakes not releasing

Since both disks are binding, its not something at the rear disk end. There's two issues I can think of.

1) something in the handbrake cable system has a problem. Cables rarely break, but can rust solid. Does the handbrake handle feel "correct" or is it loose? Did you run over something that might have snagged the cable(s)? 2) there's s hydraulic problem. Does your car have ABS? If the brake pedal return spring that holds the pedal up has come adrift (look under the dash) the pedal can sink enough to cause the brakes to drag, but this usually happens at the front, as the front brakes get applied first.