Question 1

Two technicians are discussing vacuum brake boosters. Technician A says that a low, soft brake pedal is an indication of a defective booster. Technician B says that there should be at least two power-assisted brake applications after the engine stops running. Which technician is correct?

Accepted Answer

Technician B is correct because a properly functioning vacuum brake booster should retain enough vacuum for at least two power-assisted applications after the engine has been turned off. A low, soft brake pedal typically indicates a problem with the hydraulic system, not the booster.

Question 2

Technician A says that to check the operation of a vacuum brake booster, the brake pedal should be depressed until the assist is depleted and then start the engine. Technician B says that the brake pedal should drop when the engine starts, if the booster is okay. Which technician is correct?

Accepted Answer

Both technicians A and B are correct in their methods for checking the operation of a vacuum brake booster. Technician A's method depletes the vacuum reserve, allowing for a check of the booster's ability to provide assist once the engine is started. Technician B's observation that the brake pedal should drop slightly when the engine starts indicates that vacuum is being applied to the booster, suggesting it is functioning correctly.

Question 3

Brake pedal feedback to the driver is provided by the ________.

Accepted Answer

The reaction system is responsible for providing feedback to the driver through the brake pedal, allowing the driver to feel the resistance and effectiveness of the braking system.

Question 4

The proper operation of a vacuum brake booster requires that the engine be capable of supplying at least ________.

Accepted Answer

The proper operation of a vacuum brake booster typically requires that the engine be capable of supplying at least 15 inches of mercury (in. Hg) vacuum. This level of vacuum is necessary to ensure that the brake booster can provide the power assist needed for the braking system to function effectively.

Question 5

The purpose of the charcoal filter in the vacuum hose between the engine and the vacuum brake booster is to ________.

Accepted Answer

The charcoal filter in the vacuum hose between the engine and the vacuum brake booster is designed to trap gasoline vapors to prevent them from entering the booster, ensuring that these vapors do not compromise the function of the brake system or pose a safety hazard.

Question 6

A defective vacuum brake booster will cause a ________.

Accepted Answer

A defective vacuum brake booster will cause a hard brake pedal because it reduces the power assistance to the braking system, making the pedal harder to depress.

Question 7

An accumulator such as that used on hydraulic brake boosters ________.

Accepted Answer

Accumulators in hydraulic brake boosters store pressurized hydraulic fluid, providing a reserve power source to assist braking in the event of a failure, ensuring the brakes can still be applied even if the engine or pump fails.

Question 8

The first step in diagnosing a Hydro-Boost problem is ________.

Accepted Answer

A thorough visual inspection is the first step in diagnosing a Hydro-Boost problem. This allows for the identification of any obvious issues such as leaks, damaged components, or loose connections before proceeding with more complex testing.

Question 9

A brake pedal feels spongy when depressed. Technician A says that a defective hydraulic brake booster could be the cause. Technician B says that a defective vacuum brake booster could be the cause. Which technician is correct?

Accepted Answer

A spongy brake pedal is typically caused by air in the brake lines, not a defective brake booster, whether hydraulic or vacuum.

Question 10

If the engine stops running, the Hydro-Boost will not be able to provide any power assist for the brakes.

Accepted Answer

The Hydro-Boost system uses hydraulic pressure from the power steering pump to assist in braking, and it can store enough pressure for several power-assisted stops even if the engine stops running.

Question 11

Two technicians are discussing vacuum brake boosters. Technician A says that when the engine is running and the driver's foot is off the brake pedal, a vacuum is present on both sides of the booster diaphragm. Technician B says that when the brakes are in the applied position, vacuum is present on the front side of the diaphragm. Which technician is correct?

Accepted Answer

Both technicians are correct. When the engine is running and the brake pedal is not pressed, vacuum is present on both sides of the diaphragm. When the brakes are applied, vacuum is maintained on the front side while atmospheric pressure is allowed on the rear side to assist braking.

Question 12

To provide the driver with a sense of "feel" during braking, vacuum boosters use a ________.

Accepted Answer

The reaction disc in a vacuum booster is used to provide the driver with a sense of "feel" during braking. It allows for a more controlled and responsive braking experience by giving feedback through the brake pedal.

Question 13

A hydraulically operated booster unit stores fluid under pressure by means of ________.

Accepted Answer

An accumulator is specifically designed to store fluid under pressure in hydraulic systems, acting as a reservoir that can release fluid when needed to maintain pressure or add extra power.

Question 14

A common source of vacuum for boosters used on diesel engines is ________.

Accepted Answer

Diesel engines do not create vacuum in the intake manifold like gasoline engines, because they do not have a throttle plate that restricts air flow. Therefore, an auxiliary vacuum pump is often used to provide the necessary vacuum for various components, such as brake boosters.

Question 15

Technician A says when the brakes are applied in a vacuum booster, the vacuum control valve is sealed.Technician B says the vacuum control valve is opened. Which technician is correct?

Accepted Answer

When the brakes are applied in a vacuum booster, the vacuum control valve is sealed.

Question 16

When the Hydro-Boost is in the release phase ________.

Accepted Answer

During the release phase of the Hydro-Boost system, the vent port is opened to allow pressure to be vented from the system, and the fluid port to the power chamber is closed to stop the flow of hydraulic fluid, thus allowing the system to release the applied brake pressure.

Question 17

The booster operation test determines if the booster is ________.

Accepted Answer

The booster operation test checks if the booster is receiving adequate vacuum to operate correctly and if it is effectively creating brake application force, making both A and B correct.

Question 18

Technician A says the vacuum supply test involves inspecting the vacuum supply hose for kinks. Technician B says the test involves checking the level of vacuum supplied by the engine or vacuum pump. Which technician is correct?

Accepted Answer

Both technicians are correct. Technician A's statement about inspecting the vacuum supply hose for kinks is a valid part of a vacuum supply test, as kinks can restrict vacuum flow. Technician B's statement about checking the level of vacuum supplied by the engine or vacuum pump is also correct, as it's essential to ensure the vacuum level is sufficient for the system's needs.

Question 19

Pushrod adjustment is checked with a ________.

Accepted Answer

The answer of Pushrod adjustment is checked with a ________.
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Question 20

The Hydro-Boost brake booster uses what type of fluid to multiply brake pedal force?

Accepted Answer

The Hydro-Boost brake booster uses power steering fluid to multiply brake pedal force, as it is a power brake booster system that utilizes hydraulic pressure from the power steering pump to assist in braking.

Quiz 105: Power Brake Unit Operation, Diagnosis, and Service