This is usually caused by the slider pins in the brake calipers being seized up. You will find un-evenly worn brake pads and possibly warped disks from this. Uneven brake pad pressure will heat up one side of the disk more than the other causing warpage.
Un-seize the slider pins by whatever means necessary and remove completely. Clean out the caliper housing and clean the slider pin of all rust and corrosion. Then re-lubricate with silicon grease or red grease not copper grease. After re-assembly the slider pins should be free to move by hand.