Key Points - Frequently Asked Questions

KEY POINTS - FREQUENTLY ASKED QUESTIONS

- Q: How do on-car lathes react to Axle Float? Does the play affect the machining of the rotor, 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 are just 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 to providing 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 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 okay 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 information needs to be documented on the Repair Order?

A: Any claim that is submitted using the labor operations in this bulletin, must have the Original Rotor Thickness and Refinish Rotor Thickness (if refinished) documented on the repair order. For more information, refer to the "Repair Order Required Documentation" section of this bulletin.

All Warranty Repair Orders paid by GM, are subject to review for compliance and may be debited where the repair does not comply with this procedure.