I am not sure this is your problem but it is something to check. I have had an issue where either my caliper seized or my brake line degraded on the inside creating a suction holding the caliper shut. This happened to the front passenger wheel. I only noticed it when my vehicle violently jerked st hwy speeds. I busted out my laser thermometer and found the center of the wheel to be 600 degrees.
anyways, drive it a little and check temps to see if one wheel/rotor is significantly hotter than the other.
second thing to check, see if any caliper pins or bolts have slipped or something has broken on the caliper mounting. I have had this happen on an older mustang. Reverse worked fine but driver fought me, just happened to be the way the caliper rotated in relation to the direction the wheel spun.