probably siezed up. you need to remove brake drums to see whats gone wrong. remove wheels, tap off centre cover, undo 32mm nut from centre of drum. you may need to whack the drum a few times on the side thats stuck and possibly slacken handbrake cables to get drum off. to slacken cable undo exhaust heat shield at rear of exhaust tunnel and slacken 13mm nut on cable. then check brakes both sides to see what needs replacing.
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