Question 1

When the driver depresses the brake pedal of the typical truck with air-over-hydraulic brakes,which of the following occurs?

Accepted Answer

When the driver depresses the brake pedal in a truck with air-over-hydraulic brakes, modulated air pressure actuates pneumatic booster assemblies. This system uses air pressure to enhance the hydraulic braking system, providing a more powerful braking force.

Question 2

Which of the following are functions of a typical hydraulic brake system combination valve?

Accepted Answer

A typical hydraulic brake system combination valve has multiple functions, including delaying the application of front disc brakes to balance braking between the front and rear, reducing rear wheel lock-up by modulating pressure to the rear brakes, and alerting the driver to a partial circuit hydraulic failure through a warning light or similar indicator.

Question 3

What should be used to remove pitting and corrosion from an aluminum master cylinder bore?

Accepted Answer

D

Question 4

Which of the following statements about a typical hydraulic brake system are true?

Accepted Answer

All the statements about a typical hydraulic brake system are true: the brake pedal acts as a lever to multiply the force applied by the driver, the application force is further multiplied hydraulically by the wheel cylinders, and the actual braking force at the wheels is indeed correlated with the mechanical force input at the pedal.

Question 5

A truck equipped with air-over-hydraulic brakes has illuminated a dash-warning light indicating excess brake lining wear.What would generate this signal?

Accepted Answer

The brake system ECU (Electronic Control Unit) is responsible for monitoring various aspects of the braking system, including brake lining wear. When the brake linings wear down to a certain point, sensors in the system send signals to the ECU, which then triggers the warning light on the dashboard to alert the driver of the need for maintenance.

Question 6

What could the source(s)of hydraulic fluid pressure that operates typical brake boosters?

Accepted Answer

Hydraulic brake boosters can be powered by various sources including a power steering pump, a dedicated hydraulic pump, or a reserve electric motor and pump, making all of the options correct.

Question 7

What does the term hygroscopic mean?

Accepted Answer

Hygroscopic materials are those that have the ability to absorb moisture from their surroundings.

Question 8

Which of the following guidelines is best practice for reusing brake fluid drained during bleeding operations?

Accepted Answer

Brake fluid is hygroscopic, meaning it absorbs moisture from the air, which can degrade its performance and potentially cause brake system failure. Reusing brake fluid that has been drained during bleeding operations is unsafe because it may contain contaminants and moisture that cannot be adequately removed through boiling, filtering, or settling. Therefore, the best practice is to always use new, uncontaminated brake fluid to ensure the safety and reliability of the brake system.

Question 9

What is the primary function of a pressure differential valve used in a hydraulic brake circuit?

Accepted Answer

The primary function of a pressure differential valve in a hydraulic brake circuit is to alert the driver to a partial system hydraulic failure. This is achieved by detecting differences in pressure between two sections of the brake system, indicating a potential leak or failure in one part.

Question 10

Which of the following features of a hydraulic brake system are mandatory by FMVSS 105 compliant vehicle?

Accepted Answer

FMVSS 105 requires vehicles to have dual hydraulic circuits to ensure braking capability if one circuit fails, and a mechanical means for parking, which can serve as an emergency brake, thus making all the listed features mandatory.

Question 11

Technician A says that DOT 4 hydraulic brake fluid can be destroyed in as little as one hour exposure to atmospheric air.Technician B says that DOT 5 hydraulic brake fluid is hygroscopic.Who is correct?

Accepted Answer

The answer of Technician A says that DOT 4 hydraulic...

Question 12

Which brake shoe in a non-servo drum brake assembly is energized during braking when a vehicle is traveling in a forward direction?

Accepted Answer

The answer of Which brake shoe in a non-servo drum...

Question 13

Which of the following valves delays application force to front disc brakes to balance a typical disc/drum hydraulic brake system?

Accepted Answer

The metering valve delays the application of hydraulic pressure to the front disc brakes, allowing the rear drum brakes to engage first. This helps balance the braking system by ensuring that the rear brakes contribute to the vehicle's stopping effort before the front brakes apply full force, preventing premature lockup of the front wheels.

Question 14

Which of the following valve(s)is designed to reduce rear wheel lock-up to balance a disc/drum system?

Accepted Answer

The proportioning valve is specifically designed to reduce the pressure to the rear brakes, which helps prevent rear wheel lock-up, ensuring that the front and rear brakes are balanced, especially in a disc/drum brake system configuration.

Question 15

Technician A says that a dual circuit hydraulic brake system master cylinder can be known as a tandem master cylinder.Technician B says that a tandem master cylinder has a single bore and two separate pistons.Who is correct?

Accepted Answer

A dual circuit hydraulic brake system master cylinder is indeed known as a tandem master cylinder, which aligns with Technician A's statement. Technician B is also correct in saying that a tandem master cylinder typically features a single bore with two separate pistons, designed to operate two independent hydraulic circuits for enhanced safety.

Question 16

What should be done before forcing a caliper piston back into its bore while servicing hydraulic disc brakes?

Accepted Answer

The answer of What should be done before forcing a...

Question 17

Which of the following methods would be preferred when bleeding a typical air-over-hydraulic brake system?

Accepted Answer

Pressure bleeders are preferred for bleeding air-over-hydraulic brake systems because they can efficiently and safely apply pressure to the hydraulic fluid to force air bubbles out of the system.

Question 18

Which of the following measuring tools should be used to check lateral rotor runout?

Accepted Answer

A dial indicator is the appropriate tool for measuring lateral rotor runout because it can precisely measure small distances and is capable of detecting the minute variations in the rotor's surface as it rotates.

Question 19

What is the most common type of parking brake used on trucks equipped with an air-over-hydraulic system?

Accepted Answer

The most common type of parking brake used on trucks equipped with an air-over-hydraulic system is the canister-spring brake. This system uses spring pressure for parking and is released by air pressure for driving.

Question 20

Which of the following statements regarding the function of a tandem master cylinder during normal operation is true?

Accepted Answer

The tandem master cylinder has two pistons, a primary piston and a secondary piston. The primary piston is actuated mechanically by the brake pedal, while the secondary piston is actuated hydraulically by the primary piston. There are two separate bores in the master cylinder, one for each piston.

Quiz 29: Hydraulic Brakes and Air-Over-Hydraulic Brake Systems