Truck Repair: Front disk brakes, disk brakes, flex hose

Question
I have recently obtained an 88 S10 4x4.  The left front caliper will not release the brake pad from the rotor after applying the brake. If I open the bleeder screw the pressure releases and the pads let go. I have replaced the caliper, pads, and rotor because of the damage this conditon has caused, but with the same results. Could this be caused by the combination (porportioning) valve or is it more likly a brake line problem?  

Answer
Hi Kenneth,
Almost 100% sure it is the flex hose from the frame to the caliper.
Crack it loose there at the frame, and it will probably not release the pressure if the hose is plugged.
I have cut them apart, and the rubber will deteriorate inside the hose, and stack up where the metal sleeve is that clamps the hose to the knuckle.
Van