Firebird V8-305 5.0L (1982)
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 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.
While holding the parking brake release in the return position, lightly apply the parking brake to stop the vehicle. (Failure to hold the parking
brake release in the return position 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 rear brake pulsation is indicated, test the front brakes as follows:
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.
4.
Rotate the rotor one complete revolution while observing runout indicated on the dial. Total indicated runout (T.I.R.) should not exceed 0.08 mm
(0.003 in.).
On front wheel drive vehicles, lateral rotor runout due to stacked tolerances can often be reduced by rotating (indexing) the rotor one or two
bolt holes in relation to the hub. If excessive runout cannot be corrected by indexing the rotor, check the hub and bearing assembly for
looseness.
NOTICE:
Whenever the brake rotor has been separated from the wheel bearing flange, clean any rust or foreign material from the
mating surfaces of the wheel bearing flange and rotor. Failure to do this may result in increased lateral runout of the rotor
and brake pulsation.
5.
If lateral rotor runout exceeds the amount specified in Step 4, refinish the rotor on the vehicle.
Rotor Thickness Variation Check:
Variations in rotor thickness can be checked by measuring the thickness of the rotor at four or more points around the surface of the rotor. Use a
micrometer calibrated in one tenth increments per .001 in. All measuring points must be the same distance in from the edge of the rotor.
A rotor that varies in thickness by more than 0.013 mm (0.0005 in.) can cause pedal pulsation and/or front end vibration during brake applications.
