Brake problem

I have an '85 Silverado. When I bought it the left front brake was locked up and the wheel wouldn't turn. I replaced caliper and pads, bled the system and everything seemed to work fine. I took it out and drove it and right a way the same wheel locked up again. I can't understand why it worked fine in the driveway but as soon as I drove it the brakes locked up.

I have heard that the actual rubber brake lines can collapse inside and prevent fluid from traveling back out of the caliper. I suppose that could be the problem but is there any way of verifying that before I replace the line? I wasn't sure if the proprtioning valve could cause a similar problem.

Jack the wheel with the problem, spin the tire then step on the brakes the caliper should release immediately.

My 95 did the same thing, and it was the rubber brake line.

Just an update on the brake problem I was having. My front brake was locking up completely on one side even though all brake parts were brand new.

I replaced the rubber brake line connected to the caliper and that took care of the problem. The brakes work great now.