Brake Pedal Pulsations

FRONT DISC BRAKES
Causes

Lack Of Parallelism:

- Excessive lateral runout (warpage) or lack of parallelism (rotor thickness variation).
- Loose or worn front suspension components. Worn components which allow lateral movement of the wheel/hub assembly may produce a pulsating pedal or a shimmy in the front end of the vehicle upon braking.
- Loose or worn wheel bearings

What to Check For

Lack Of Parallelism:

- Measure the rotor with a micrometer and a dial indicator. Resurface or replace the rotor if runout exceeds 0.004" or if thickness variation exceeds 0.0005" when measured at several places of equal distance from rotor edge.
NOTE: Excessive lateral runout may be caused by unevenly torqued lug nuts or loose wheel bearings. Check wheel bearing adjustment and lug nut torque prior to measuring the rotor.
- Check all front suspension components for worn bushings or looseness and replace if necessary.
- Check and adjust front wheel bearings.

REAR DRUM BRAKES
Causes
- Drum out of round.
- Cracked drum.
- Hard spots on the drum friction surface.



What to Check For
- Measure the drum inside diameter at several points around the circumference of the drum. If the measurements vary by more than 0.002", resurface or replace the drum.
- Inspect the drum for cracks. Lightly drop the drum (from a height of 4-5 inches) onto a flat hard surface. A cracked drum will make a dull thud sound while a good drum will make a ringing sound. If the drum is cracked it must be replaced.
- Inspect the drum friction surface for slightly raised small dark spots (approximately 1/4 in diameter). These hard spots are defects created by localized magnetic fields that built up during the casting process. Resurface or replace the drum (generally these hard spots can not be machined and the drum must be replaced)