Tech Tip: Brake Noise or Pulsation
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Tech Tip: Brake Noise or Pulsation

Beginning with some models, GM has introduced a new brake rotor technology called Ferritic Nitro-Carburizing (FNC). Simply put, it is an additional step in the manufacturing process of the brake rotor that creates a hardened outer layer on the surface of the rotor.

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2009-2011 Buick Lucerne Super with 18" Wheels
2011 Buick LaCrosse
2009-2011 Cadillac DTS
2011 Chevrolet Impala, Malibu, Volt

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Beginning with some models, GM has introduced a new brake rotor technology called Ferritic Nitro-Carburizing (FNC). Simply put, it is an additional step in the manufacturing process of the brake rotor that creates a hardened outer layer on the surface of the rotor. This hardened outer layer reduces the rotor rusting and it also allows the rotor to wear slower. Because this new technology protects against excessive rotor corrosion, it not only aesthetically looks better through open spoke-type wheels, it helps reduce thickness variation, which creates pulsation specifically due to “lot rot” corrosion.

Diagnostic Procedure
1. Describe the customer’s concern on the repair order (i.e. squeak, growl, pulsation, vibration, shudder, etc.).

2. Can the noise/pulsation be heard/felt (duplicated) while the vehicle is moving with the brake pedal applied?
-Yes – Proceed to Step 3.
– No – This concern is not caused by the brake rotor or pad. Do not proceed with this bulletin. Refer to service information for diagnosis and repair.

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3. If the concern is noise, proceed to Step 4. If the concern is pulsation, can the concern be felt through the steering wheel or pedal? Use the parking brake to determine whether this is a front or rear brake rotor issue. Describe/document on the Repair Order what is being felt and at what speed (with brake apply) and if it is a front or rear issue.

4. Perform a visual inspection of the brake rotor(s) and pads. Describe on the repair order  any unusual wear or corrosion. If the brake pads are NOT worn, proceed with Step 5. If the brake pads are unevenly worn side to side and/or inner to outer, determine cause, correction and describe on repair order. Proceed with Step 7.

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5. Burnish brakes by performing 10-15 moderate stops from 56-64 km/h (35-40 mph) with cooling time between stops. Did this correct the customer’s concern?
-Yes – No further action is required.
– No – Proceed to Step 6.

6. If the customer’s concern is noise related, proceed with Step 7. If the customer’s concern is pulsation related, proceed with Step 8.

7. Replace the brake pads. Did this correct the customer’s concern?
-Yes – No further action is required. Proceed to Step 9.
– No – Proceed to Step 8.
Important: Only clean-up/refinish rotor(s) determined to be the cause of issue.

8. Clean-up/refinish the rotor(s). Before and after refinish, rotor thickness measurements must be documented on the repair order.

9. The following information must be documented on the repair order: detailed condition, cause, correction information and rotor measurements, per the above steps.

Courtesy of ALLDATA.

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