While most vehicles have gauges on the pads to warn you when the brake pads are getting thin it's a good idea to have a four wheel brake inspection each time you rotate your tires. A comprehensive brake inspection will include checking all hydraulic units including: Master Cylinder, Calipers, Wheel Cylinders and Lines & hoses. Brake fluid should be checked for condition and if contaminated the system should be flushed and bled. Rotors & drums should be checked for thickness and damage whenever the lining and hardware are examined. A before and after test drive for brake operation is always in order.