Diagnosis

DIAGNOSIS

Test Drive:

Before any diagnosis is performed, it is essential that the vehicle be road tested to determine the exact nature of the problem and to get a feel for the vehicle vibration characteristics. The road test is used to determine whether brake pulsation is present or whether the vibration is due to some other cause (tire and wheel vibration/balance, bent or out-of-round wheel rims, drivetrain, etc.).

When a brake pulsation condition is confirmed, a road test will determine whether the front or rear brakes are the cause.

If vibration/roughness is determined to be from a source other than brakes, perform necessary repairs.
Brakes should be tested while driving on a dry, clean and a reasonably smooth road surface. Rear brake pulsation is more easily isolated. When rear brake pulsation has been eliminated or repaired, a full brake system test can be used to diagnose front brake pulsation. Begin by testing the rear brakes as follows:

Rear Brake Pulsation Test:

1. Accelerate to approximately 20 mph.

2. Place gear selector in neutral.

3. a. On Cimarrons, hold park brake release in return position while lightly applying the parking brake to stop the vehicle.
b. On all other models, hold the gear selector in Neutral while applying the parking brake lightly to stop the vehicle. Moving the gear selector to any drive position allows vacuum release of the parking brake. (Failure to release the parking brake could result in rear brake lock.)

4. OBSERVE: Does the parking brake pedal pulsate? Is there noticeable vibration in the vehicle (different than road induced)?

5. If either of these conditions is present, refinish or replace drums/rotors as required.

If no brake pulsation is indicated, test the front brakes.

Front Brake Pulsation Test (Full Brake System):

1. Perform 20 to zero mph brake test:

a. Accelerate vehicle to 20 mph.
b. Place selector in neutral.
c. Apply brakes lightly to stop the vehicle. If pulsation is felt, service front brakes as described in this bulletin. If no pulsation is present, continue to step 2.

2. Perform 45 to 50 mph brake test:

a. Accelerate vehicle to 50 mph.
b. Place selector in neutral.
c. Apply brakes using medium pedal pressure. If pulsation is felt, service front brakes as described in this bulletin. If no pulsation is present, continue to step 3.

3. Heat up the brake system by performing 10 stops from approximately 30 mph using medium pedal pressure. Then repeat 20 to zero mph test in step 1.

a. If pulsation is felt, service front brakes as described in this bulletin.
b. If no pulsation is present, check tires and drivetrain components for other possible causes of customer complaint.