NAPA - National Automotive Parts Association Certified Mechanic Brake System Service Questions and Answers

Question 1

A customer complains of a pulsating brake pedal when stopping. Which of the following is the MOST likely cause?

Accepted Answer

Excessive rotor runout or thickness variation

Answer

Excessive rotor runout (wobble) or disc thickness variation (DTV) causes the brake pads to move in and out as the rotor turns. This hydraulic pulsation is transmitted back through the caliper and brake fluid to the brake pedal, which the driver feels as a pulsation.

Question 2

A technician is performing a brake fluid flush. What is the primary reason for periodically replacing brake fluid?

Accepted Answer

The fluid is hygroscopic and absorbs moisture, lowering its boiling point.

Answer

Brake fluid is hygroscopic, meaning it absorbs moisture from the atmosphere. This water contamination significantly lowers the fluid's boiling point. Under heavy braking, the heat generated can cause the water in the fluid to boil, creating vapor pockets. Since vapor is compressible, this leads to a spongy pedal and a dangerous loss of braking ability.

Question 3

When bleeding the brakes on most non-ABS passenger vehicles, what is the generally accepted sequence?

Accepted Answer

Start with the wheel furthest from the master cylinder and work to the closest.

Answer

The standard procedure for bleeding most brake systems is to start with the bleeder screw on the wheel furthest from the master cylinder and progressively move to the one closest. This method helps to systematically push all the air out of the longest hydraulic lines first, ensuring a more effective and complete air purge from the system.

Question 4

After installing new brake pads and rotors, a technician should perform a bedding-in procedure. What is the main purpose of this process?

Accepted Answer

To deposit an even layer of friction material onto the rotor surface.

Answer

The bedding-in, or break-in, process involves a series of controlled stops to heat the new pads and rotors. This heat cycle transfers a thin, uniform layer of the brake pad's friction material onto the rotor's surface. This transfer layer is crucial for optimal braking performance, noise reduction, and preventing uneven deposits that can cause vibration.

Question 5

A vehicle is brought into the shop with a complaint of a "spongy" or "soft" brake pedal. Which of the following is the MOST common cause of this symptom?

Accepted Answer

Air in the hydraulic brake lines

Answer

Air is highly compressible, unlike brake fluid. When air becomes trapped in the hydraulic lines, pressing the brake pedal compresses the air first before applying full hydraulic pressure to the calipers. This compression of air is what causes the pedal to feel soft or spongy.

NAPA - National Automotive Parts Association Certified Mechanic Practice Test

NAPA - National Automotive Parts Association Certified Mechanic Practice Test

NAPA - National Automotive Parts Association Certified Mechanic Brake System Service Questions and Answers