Brake cables especially Wheel cables have 3 main problems...
1. Core "freezes" w/ rust dirt etc inside the jacket.
2. Jacket breaks at the mounting end(s). Pull on jacket and watch both ends. Jacket pulls out of an end then cable is F'd.
3. Core literally freeze w/ "water" in winter.
Likely have 1 2 or both dragging on release.
Push caliper level a little to release core "button."
Remove button so can't load the level.
Push level down hard then carefully release pressure, level should move.
If that works likely need 2 wheel cables at minimum.
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave