Pinpoint Test A: Brake Vibration/Shudder

• Check that the wheel and tires are correct for the vehicle. Inspect the tires for abnormal wear patterns.
• Road test the vehicle. Warm the brakes by slowing the vehicle a few times from 80-32 km/h (50 to 20 mph) using light braking applications. At highway speeds of 89-97 km/h (55-60 mph), apply the brake using a light pedal force.
• Is there a vibration/shudder felt in the steering wheel, seat or brake pedal? 

Yes  : GO to  A4.

No  : GO to A2.

• Road test the vehicle. At highway speeds of 89-97 km/h (55-60 mph), apply the brake using a moderate to heavy pedal force.
• Is there a vibration/shudder? 

Yes  : For vehicles with ABS, GO to A3.

For vehicles with standard brakes, GO to  A4.

No  : Vehicle is OK. VERIFY condition with customer. TEST the vehicle for normal operation.

• During moderate to heavy braking, noise from the hydraulic control unit (HCU) and pulsation in the brake pedal can be observed. Pedal pulsation coupled with noise during heavy braking or on loose gravel, bumps, wet or snowy surfaces is acceptable and indicates correct functioning of the ABS system. Pedal pulsation or steering wheel nibble, (frequency is proportioned to the vehicle speed) indicates a concern with a brake or suspension component.
• Is the vibration/shudder vehicle speed sensitive? 

Yes  : GO to  A5.

No  : The brake system is operating correctly

NOTE: Begin at the front of the vehicle unless the vibration or shudder has been isolated to the rear.
• This test is not applicable to vehicles with drum-in-hat type parking brakes. For vehicles with drum-in-hat parking brakes, proceed to the next test. For all other vehicles, apply the parking brake to identify if the problem is in the front or rear brake. At highway speeds of 89-97 km/h (55-60 mph), lightly apply the parking brake until the vehicle slows down. Release the parking brake immediately after the test.
• Is there a vibration/shudder? 

Yes  : GO to  A8.

No  : GO to A5.

• Check the front wheel bearings. Refer to WHEEL BEARING CHECK .
• Are the wheel bearings OK? 

Yes  : GO to A6.

No  : INSPECT the wheel bearings. ADJUST or REPAIR as necessary. TEST the system for normal operation.

• With the vehicle in NEUTRAL, position it on a hoist. Refer to JACKING & LIFTING .
• Check the front suspension for:
  • broken or loose bolts.
  • damaged springs.
  • worn or damaged upper and lower control arm bushings.
  • loose or rough front bearings.
  • uneven tire wear.
• Are all the suspension components in satisfactory condition? 

Yes  : GO to A7.

No  : REPAIR or INSTALL new components as necessary. TEST the system for normal operation. If equipped with fire suppression system, GO to  A10.

CAUTION: Do not use a bench lathe to machine brake discs.
NOTE: Follow the manufacturer's instructions to machine the brake discs. After machining, make sure the brake disc meets the thickness specification.
• Resurface the front brake discs. Road test the vehicle.
• Is the vibration/shudder present? 

Yes  : GO to A8.

No  : Vehicle is OK. If equipped with fire suppression system, GO to  A10.

• With the vehicle in NEUTRAL, position it on a hoist. Refer to JACKING & LIFTING .
• Check the rear suspension for:
  • broken or loose bolts.
  • damaged or worn springs or spring bushings.
  • worn or damaged upper and lower control arm bushings.
  • worn or damaged trailing arms.
  • loose or rough rear bearings.
  • uneven tire wear.
• Are all the suspension components in satisfactory condition? 

Yes  : GO to A9.

No  : REPAIR or INSTALL new components as necessary. TEST the system for normal operation. If equipped with fire suppression system, GO to  A10.

CAUTION: Do not use a bench lathe to machine brake discs.
NOTE: Follow the manufacturer's instructions to machine the brake discs. After machining, make sure the brake disc meets the thickness specification.
• Resurface the rear brake discs or drums. Road test the vehicle.
• Is the vibration/shudder present? 

Yes  : CHECK the front suspension for wear or damage. RESURFACE the front brake discs. TEST the system for normal operation. If equipped with fire suppression system, GO to A10.

No  : Vehicle is OK. If equipped with fire suppression system, GO to A10.

WARNING: If equipped with fire suppression system, repower the system. For important safety warnings and procedures, refer to FIRE SUPPRESSION SYSTEM .
• Verify that the fire suppression system is repowered. For additional information, refer to FIRE SUPPRESSION SYSTEM .
• Is the fire suppression system repowered? 

Yes  : Fire suppression system repowering is complete.

No  : REFER to FIRE SUPPRESSION SYSTEM for fire suppression system depowering and repowering procedure.