Like the title says my rear brakes keep getting locked up. I recently just upgraded them to disc brakes from a gsr. The car ran fine when I took it around the block a few times for a test. When I turned it on earlier today the rear wheels were wouldnt move. I then loosened the parking cable nut completely and it still was locked. Then I left the car alone for a few hrs and when I came back they were no longer locked. As I took it for a drive again they locked up again on me. Any ideas what could be wrong? What do you guys recommend I check? Thanks.