Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
A customer complains of a pulsation felt through the brake pedal during moderate to heavy braking. The technician inspects the front brakes and finds no signs of excessive runout or thickness variation on the rotors. What other component should be closely inspected for causing this pulsation?
- AThe rear brake drums.
- BThe master cylinder.
- CThe power steering pump.
- DThe wheel bearings.
Show answer & explanationAnswer & explanation
Correct answer: A. The rear brake drums.
While front rotor issues are the most common cause of pedal pulsation, rear brake drums that are out-of-round or have excessive runout can also transmit pulsation through the hydraulic system to the brake pedal, especially during moderate to heavy braking. The other options are unrelated to brake pedal pulsation.
Why the other options are wrong
- B. A faulty master cylinder usually causes a soft pedal or internal bypass, not a pulsation.
- C. The power steering pump is unrelated to brake pedal pulsation.
- D. Worn wheel bearings typically cause noise (humming/growling) or looseness, not a distinct pedal pulsation during braking.
Brake Pulsation Causes
Reasons for a vibrating or pulsating sensation felt through the brake pedal or steering wheel during braking.
- Rotor runout (most common).
- Rotor thickness variation.
- Out-of-round brake drums (rear).
- Loose wheel bearings or suspension components (less common for pedal pulsation).
Memory trick: Pulsing feet, check front and rear heat.