What causes the front disc brakes to get hot and smoke on a 98 neon Iv'e replaced the calipers because the old one had the same problem and it seems to be only the driver side?

my daughter has a 98 neon and it had the same exact problem. What i found was that the left front rubber line was so old that it was collapsing when the brakes got up to operating temp in essence making the brake drag until it almost locked. She got it so hot it melted the hubcap. I replaced with new rubber line and haven't had the problem since.