Check the nut, cotter pins, positioning plate on the brakes whether it is complete, lose or not, lever and spring is free of cracks, pin bolts on the wheel and the brake washer is loose cushion, or complete; if it is reliable when the brake is open. The opening of the movable tiles should be less than 1.0mm and the distance across the gap between the brake drum should be equal, each axle pin may not have stuck phenomenon.