GM 18020612 Drum,Rear Brake

Whenever the disc brake pads are checked for wear, it is also necessary to look at the state or condition of the discs or rotors. Thus, ligth scoring or grooving are expected but deep grooves or severity erosion are not permitted. Some models have a specific channel, the so-called squeal groove, which should not be confused with damage. The existence of a vibration when the brake is applied has also been attributed to disc run out. To check for this, a dial gauge or feeler blades may be used between the disc and any fixed point. It was established that the disc should be turned at a slow rate in order not to exceed the runout of 0.004 inches. Thickness variations that are above the 0.0005 inches may also imply that the disc will vibrate during braking. Discs usually have wear limit and refinish thickness dimensions moulded on them. On the other hand, if a dealer fails to refinish a disc to certain standards of the set tolerance, a new disc has to be fitted. When a brake drum is pulled on a particular scheme for a lining inspection, it is necessary to look for cracks, 'scoring,' and out-of-round conditions. An out-of-round drum results in pulsations felt through the brake pedal during the application and the internal diameter has to be checked at various positions using an internal micrometer. Drums may be refinished internally; however, the wear and refinish sizes that may be cast into them must not be exceeded.