ASE Practice Test (A5: Brakes)

Question 1

Which of the following is caused by a power assist brake booster push rod that is too short?

Accepted Answer

Excessive brake pedal travel

Answer

If the power assist brake booster push rod is too short, there will be an excessive gap between the push rod and the master cylinder piston when the brake pedal is at rest. This means the brake pedal must travel a greater distance to bridge this gap and begin engaging the master cylinder, resulting in a symptom of excessive brake pedal travel.

Question 2

Which of the following indicates a spongy brake pedal on a car with 4-wheel disc brakes and a longer than normal travel?

Accepted Answer

Air in the hydraulic system

Answer

A spongy brake pedal with longer than normal travel is a classic symptom of air trapped within the hydraulic brake system. Unlike incompressible brake fluid, air bubbles compress when the pedal is applied, absorbing some of the pedal force before it can be fully transmitted to the calipers. This compression results in a soft, spongy feel and requires increased pedal travel to achieve effective braking.

Question 3

A vacuum brake booster is installed on a vehicle. It doesn't have power assist until the engine has been running for a minute, after which it functions normally. What is the most probable cause?

Accepted Answer

Defective check valve

Answer

The most probable cause is a defective check valve in the vacuum brake booster. The check valve is designed to maintain vacuum within the booster even when the engine is off, providing immediate power assist upon startup. If the check valve is faulty and leaks, the vacuum bleeds off, requiring the engine to run for a period to re-establish sufficient vacuum in the booster before power assist becomes available.

Question 4

During braking, the brake pedal on a vehicle with power-assisted disc/drum brakes gently glides to the floor. Which of these possibly be the source of the problem?

Accepted Answer

An internal master cylinder leak

Answer

When the brake pedal gently glides to the floor, it typically indicates an internal leak within the master cylinder. This occurs when the piston seals (cups) are worn or damaged, allowing brake fluid to bypass the piston instead of being forced into the brake lines to actuate the calipers and wheel cylinders. Consequently, hydraulic pressure cannot be maintained, and the pedal slowly loses resistance.

Question 5

What may be the cause of a spongy brake pedal?

Accepted Answer

Air in hydraulic system

Answer

A spongy brake pedal is a classic symptom of air trapped within the hydraulic brake system. Unlike brake fluid, which is incompressible, air bubbles compress when the brake pedal is applied. This compression absorbs some of the force intended for the brakes, resulting in a soft, yielding pedal feel and reduced braking efficiency.