Most GMC brake rotors and discs are found only on the front of your truck. The reason being is that the drum style of braking system is still being used on the rear of many work trucks. Recently, that has started to change; however only for upgraded or deluxe models. The brake rotors have a flat, disc-like surface where the brake pads apply the pressure they receive from the hydraulic calipers on the braking system on the GMC truck. This force is what brings the vehicle to a stop. If the pads become worn and the backing plate they are mounted to begins to rub on the brake discs, then damage occurs in the form of grooves. With the presence of grooves in the otherwise flat surface of the brake rotors then the stopping ability of the GMC is impaired. If the load is too great and an excessive amount of heat is generated, then either no braking could be the result or the wheel could lock up causing the truck to spin out of control. An audible indication of this condition would be when a metal to metal grinding noise is heard when the brakes are being applied. A brake job is now required on the vehicle which should include the packing of the wheel bearings with grease. Any and all grooves in the GMC brake rotors and discs must be removed for the longevity of the new brake pads being installed. This is accomplished by turning the brake discs on a lathe. If the grooves are too deep or the rotors have been turned before they may be too thin and replacement of this braking component is required. If that is not done, the braking system could heat up beyond its tolerances and cause a failure of the braking system again causing an unfortunate accident involving the GMC truck.