00-05-22-002N Disc Brake Warranty Service and Procedures - (May 31 2013) Disc Brakes - part 11
A groan type noise may be heard when stopping quickly or moving forward slowly froma complete stop. This is normal. On vehicles equipped with ABS, a groan or moan typenoise during hard braking applications or loose gravel, wet or icy road conditionsis a normal function of the ABS activation.KEY POINTS — FREQUENTLY ASKED QUESTIONSQ: How do on-car lathes react to Axle Float- Does the play affect the machining of therotor, either surface finish or LRO-
A: Because the Pro-Cut on-car lathe adjusts in a live mode while spinning the hub/rotor,the dynamics of a floating axle are effectively eliminated. Once the lathe is compensated,there is no difference in the cutting/surface finish and LRO arejust the same as with a non-floating axle.Q: Which lathe is essential for performing brake work, the bench or on-car-
A: Dealers must have a well maintained bench lathe and well maintained on-car lathe.These lathes need to be calibrated on a monthly basis. BOTH lathes are essential toproviding quality brake service.Q: What is the expected tip life for an on-car lathe-
A: The geometry and composition of the Pro-Cut tips are designed for “single pass” cutting.When using the Pro-Cut the cutting depth should be set to take all material neededto get below rust grooves, eliminate all run-out and resurface the entire disc ina single pass. Cuts of 0.1016-0.381-mm (0.004-0.015-in)will provide the best surface finish and the optimal tip life. No “skim cut” or “finishcut” is needed. Failure to follow this procedure will shorten tip life. The Pro-cuttips will last between 7-12 cuts per corner. With three usable corners, a pair oftips is good for at least 21 cuts.Q: Why does GM recommend the use of single pass (referred to as “positive rake”) benchand on-car brake lathes-
A: GM Service and GM Brake Engineering have performed competitive evaluations on a significantnumber of bench and on-car brake lathes. These tests measured critical performancecharacteristics such as flatness, surface finish and the ability of the latheto repeat accuracy over many uses. In each test, single pass lathe designs out performedthe competitors. Single pass brake lathes are more productive requiring less timeto perform the same procedure.Q: Is it okay to leave the caliper/pads installed while cutting rotors using an on-carlathe-
A: On-car lathes should never be used with the pads and calipers installed on the vehicle.The debris from cutting the rotors can contaminate the brake pads/calipers which canlead to other brake concerns and comebacks.