Check and see if the caliper is stuck, If it doesn't retract and the pads are always in contact then you have instant braking. Also check the caliper sliders and make sure those are greased to allow the caliper to move when you take pressure off the peddle.

Also check the rear drums and E brake cables, if the E break is stuck dragging the rear shoes on the drums replace or repair the cables. The same thing can happen if the shoes are dragging on the drums from being to tight. You should be able to spin the rear tire (On jack stands in Neutral) and feel some light dragging on the brakes. If they are hard to turn then they need to be adjusted or repaired depending on why they are dragging.