60,000 to 120,000, depending on the engine type and manufacturer's recommendation. It is a belt that will break totally disabling your vehicle. When it breaks on some engine types, it can also do damage to the valves or other engine components. Listen for grinding noises when braking. It is best to have them inspected with each oil change.
Safety is the main concern.
However, if the pads go to metal, they will damage the metal brake rotors, which will have to be replaced adding a major expense. Rotors are the part of the wheel that the pads make contact to stop the vehicle. Rear Brake Drum Service and Brake Shoe Replacement. 15,000 best for cleaning and inspection. Replace shoes as needed, intervals can vary depending on driving habits and conditions.