Brakes - Pulsation/Vibration in Steering Wheel When Braking
TECHNICALBulletin No.: 12-05-23-001
Date: December 04, 2012
Subject: Pulsation or Vibration Felt in Steering Wheel During Moderate Brake Apply at Highway Speeds
Models:
2013 Cadillac XTS Limo (RPO V4U, W30) Hearse (RPO B9Q) Armored Car (RPO B05) Models
Condition
Some customers may comment on a pulsation or vibration mostly concentrated in the steering wheel during downhill descent as specifically described. This condition will most often begin as an increasing rumbling noise coming from the underbody or the front of the vehicle. This condition may also be exhibited in mountainous regions.
Note
Use care to ensure the following diagnosis and repair are only attempted if the conditions and concern match those listed, and if the concern can be duplicated under the same conditions.
This condition occurs ONLY under the following conditions:
- When the brake is applied at a moderate rate, while driving at highway speeds of 80 km/h (50 mph) or more.
- The condition starts as the brakes get hot (during application).
- Typically a rumbling noise will be heard first, building in intensity, followed by increasing pulsation, or vibration, felt in the steering wheel, then typically felt in the floor panel.
Cause
This condition may be caused by interaction between the front brake lining material and the front brake rotors.
Correction
Important
DO NOT attempt any repairs on the vehicle until you verify the specific condition is present by following the steps below:
1. Warm up the vehicle by driving approximately 8 km (5 mi).
2. Drive the vehicle at highway speed, where possible. Make sure that the brakes are not heated prior to the observation.
3. With a speed limit of 64 km/h (40 mph) or greater, with the side windows down, while in Drive, apply the brakes naturally, only as needed, to maintain the speed limit. Observe for noise, followed by pulsation/vibration, as the brakes are warmed up by brake application.
Note
If the front pad kit listed is used to correct any condition other than the condition described in this bulletin, the vehicle could experience higher mileage corrosion-induced brake pulsation.
If the condition described HAS NOT been verified, or if the condition observed IS NOT most noticeable through the steering wheel, the observed condition may have a different cause, such as a tire/wheel or rear brake issue, etc. Refer to SI for any further related diagnostics.
If the condition described has been verified, and if the condition is most noticeable through the steering wheel, and if the condition was not present when brakes were not warmed up, typically for initial brake apply, perform the following inspection and repair.
Important
- It is critical to use the proper OEM brake rotors. Use of Non-OEM rotors may prevent the condition from being corrected long term.
- If Non-OEM rotors are identified, these rotors are NOT covered under the GM New Vehicle Limited Warranty.
1. Inspect the front brake rotors to ensure that they are OEM rotors.
- Remove the brake rotor from the vehicle.
- Inspect the back side of the rotor for the Bosch Logo. If the Bosch logo IS NOT present, replace with OEM GM rotors, P/N 25819670.
2. Inspect the front brake rotors for Assembled Lateral Runout (LRO) and thickness variation. Follow SI procedures.
3. Inspect the front brake rotors for minimum thickness. Follow SI procedures.
4. If the rotors are within specifications, DO NOT refinish or replace the rotors.
5. If the rotors are out of specifications, refinish the rotors on a qualified lathe, or replace the rotors as appropriate. Follow SI procedures.
Note
To prevent a noise concern, follow the brake pad insulator preparation and seating instructions as referenced in Front Brake Pad Replacement (1500) in SI.
6. Install the specified front pad kit, GM P/N 25910432. Follow SI procedures.
7. Ensure that the condition has been eliminated under the same conditions.
Parts Information
Warranty Information
For vehicles repaired under warranty, use the table above.
Note
H9745 includes time for road testing and for removal of 1 rotor to inspect for OEM markings.
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