Frequently Asked Questions

KEY POINTS - FREQUENTLY ASKED QUESTIONS

- 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 to providing quality brake service.
- Q: Why is it necessary to use a dial indicator to check runout?
A: Both the bench lathe and the on-car lathe will yield EXCELLENT results, but NO LATHE guarantees that the "installed rotor" will meet GM's lateral runout specification. This is why GM insists on the dial indicating of all rotors.
- Q: When should the measurement be taken using a dial indicator?
A: ALL rotors are to be dial indicated after resurfacing and mounting on the vehicle hub, regardless of whether the technician uses the bench lathe or the on-car lathe.
- 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 needed to get below rust grooves, eliminate all run-out and resurface the entire disc in a 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 "finish cut" is needed. Failure to follow this procedure will shorten tip life. The Pro-Cut tips will last between 7-12 cuts per corner. With three usable corners, a pair of tips is good for at least 21 cuts.
- Q: Why does GM recommend the use of single-pass (referred to as "positive rake") bench and on-car brake lathes?
A: GM Service and GM Brake Engineering have performed competitive evaluations on a significant number of bench and on-car brake lathes. These tests measured critical performance characteristics such as flatness, surface finish and the ability of the lathe to repeat accuracy over many uses. In each test, single-pass lathe designs out-performed the competitors. Single-pass brake lathes are more productive requiring less time to perform the same procedure.
- Q: Is it OK to leave the caliper/pads installed while cutting rotors using an on-car lathe?
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 can lead to other brake concerns and comebacks.
- Q: What is the best way to correct for excessive lateral runout on vehicles with hubless rotors?
A: Regardless of the type of lathe used to resurface hubless rotors, on-car or bench lathe, the preferred method to correct for excessive lateral runout is the Brake Align Runout Correction Plate System. This warranty policy for correction of lateral runout applies to ALL model vehicle, therefore it is essential to inventory a FULL assortment of Brake Align Correction Plates, and a full assortment of sizes, (.003",.006", and.009").
- Q: Is it necessary to measure for LRO on new OEM rotors?
A: All new GM rotors must also be dial indicated after installation. New rotors are NEVER to be resurfaced on any type of lathe.
- Q: What labor operation can be used to claim the time for measuring and/or correcting for LRO?
A: Applicable labor operations include the time for performing a final LRO measurement in the base time allowance. Refer to the "Warranty Information" section of this bulletin in instances where additional time for correcting LRO to meet specification is necessary.
- Q: What information needs to be documented on the customer service order?
A: Any claim that is submitted using the labor operations in this bulletin, must have the Original Rotor Thickness, Refinish Rotor Thickness and LRO documented on the customer service order. For more information, refer to the "Customer Service Order / Warranty Claim Required Documentation" section of this bulletin.
All Warranty customer service orders paid by GM, are subject to review for compliance, documentation of lateral runout measurements and the use of Brake Align Plates and may be debited where the repair does not comply with this procedure.