Compounding the air brakes means fully applying both the service brakes and the spring brakes (such as when setting the parking brakes) at the same time. Each service brake can exert a force of up to 3,000 pounds, and each spring brake can exert up to 2,000 pounds, for a total of up to 5,000 pounds. This large force can damage slack adjusters, S-cams, brake chamber mounting bolts, brake shoe rollers, brake shoes, and brake drums.