Corvette V8-6.2L (2008)
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.
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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.
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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.
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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.
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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.
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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.
Brake Warranty
BRAKE WARRANTY
Brake Rotors:
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Brake rotor warranty is covered under the terms of the GM New Vehicle Limited Warranty. Reference the vehicle's warranty guide for
verification.
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Rotors should not be refinished or replaced during normal/routine pad replacement.
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Rotors should not be refinished or replaced and is ineffective in correcting brake squeal type noises and/or premature lining wear out.
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Rotors should not be refinished or replaced for cosmetic corrosion. Clean up of braking surfaces can be accomplished by 10-15 moderate stops
from 56-64 km/h (35-40 mph) with cooling time between stops.
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Rotors should not be refinished or replaced for rotor discoloration/hard spots.
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Rotors should be refinished NOT replaced for Customer Pulsation concerns. This condition is a result of rotor thickness variation, usually caused
by LRO (wear induced over time and miles) or corrosion (Lot Rot).
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When rotor refinishing, only remove the necessary amount of material from each side of the rotor and note that equal amounts of material do not
have to be removed from both sides on any brake system using a floating caliper.
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Rotors should be refinished for severe scoring - depth in excess of 1.5 mm (0.060 in).
Important
If the scoring depth is more than 1.5 mm (0.060 in) after the rotor is refinished, it should be replaced.
