Older brake pads or shoes may contain asbestos, which has been determined to be a cancer causing agent. Never clean the brake surfaces with compressed air! Avoid inhaling any dust from any brake surface. When cleaning brake surfaces, use a commercially available brake cleaning fluid.
See Figures 1, 2 and 3
Fig. Fig. 1: Rear drum brake components-except Sonata
Fig. Fig. 2: Rear drum brake components-Sonata
Fig. Fig. 3: Rear drum brake components