D - Hydraulic Brake Booster System Fundamentals and Service

Question 1

Name three categories of power assist brake systems.

Answer 1

Vacuum booster systems, air-over-hydraulic booster systems, hydraulic-over-hydraulic booster systems.

Question 2

Explain why vacuum type power brake boosters are not generally used on vehicles with a diesel engine.

Answer 2

Diesel engines do not create sufficient vacuum to effectively operate vacuum boosters.

Question 3

To determine if a vacuum booster is vacuum is Vacuum Suspended:

Answer 3

The engine must be running and the vacuum must be on both sides of the power diaphragm.

Question 4

Describe a quick test of a vacuum booster system to see if any boost exists at all.

Answer 4

With engine and key off, apply brakes several times to remove all vacuum. Apply brakes and hold foot down. Start engine and/or turn key on. Vacuum source is activated and brake pedal moves toward floorboard.

Question 5

True or False: Vacuum boosters work because a difference exists between a low-pressure area and a high-pressure area.

Answer 5

True.

Question 6

True or False: Air-over-hydraulic booster systems are typically used when the vehicle has a gasoline engine.

Answer 6

False; Generally used with diesel engine and air compressor.

Question 7

Air used in the air-over-hydraulic booster system is:

Answer 7

Compressed air.

Question 8

True or False: Water in the air supply system used with air-over-hydraulic booster systems does not have a negative affect on booster operation.

Answer 8

False; Water in air supply can affect valve operation/sealing.

Question 9

A power cluster is a combined air cylinder and hydraulic cylinder assembly. Explain how the air cylinder is activated.

Answer 9

The operator pushes a brake pedal, which activates an air control valve. Compressed air is directed from the air reservoir to the air cylinder on the power cluster.

Question 10

True or False: In the air-over-hydraulic brake booster system, a special hydraulic oil is used in the hydraulic system.

Answer 10

False; In the system, brake fluid is the hydraulic fluid used.

Question 11

Explain where brake fluid is used in the air -over-hydraulic brake system.

Answer 11

Brake fluid is used in the master cylinder and the lines leading to the wheel brakes.

Question 12

When bleeding the brakes in an air-over-hydraulic brake system, reduced air pressure is used in the air system. Explain why this is done.

Answer 12

A low air pressure is used so the brake fluid will not leave the bleeder screw at a high velocity. Eye protection is required.

Question 13

Hydraulic-over-hydraulic power brakes use fluid in two separate systems. This is described more accurately as:

Answer 13

Hydraulic fluid over brake fluid.

Question 14

In the hydraulic-over-hydraulic system, pressure for the hydraulic system is normally supplied be a/an:

Answer 14

Power steering pump.

Question 15

What type of fluid might be used in the brake system of a hydraulic-over-hydraulic brake system?

Answer 15

DOT 3, DOT4, or DOT 5 brake fluid. DOT 3 and 4 can be mixed. DOT 5 is used alone.

Question 16

The hydraulic-over-hydraulic brake system uses high-pressure and low-pressure steel lines and flex hoses. Explain where high-pressure lines would be used.

Answer 16

High-pressure lines are used in the pressure supply side of the hydraulic system. High-pressure lines are used in the brake fluid lines.

Question 17

Explain the function of an accumulator as used in a hydraulic-over-hydraulic brake system.

Answer 17

The accumulator is used to provide high pressure to the power brake system if the power steering pump fails or the engine quits. This output is limited to two or three power-assisted pedal applications.

Question 18

For personnel working around accumulators, several dangers may be present. Explain the dangers and how you would protect yourself.

Answer 18

High spring tension and high hydraulic fluid pressure exist in the accumulator. Relieve oil pressure before opening any line. Secure the spring while opening the accumulator. Follow manufacturer’s instructions.

Question 19

Explain the function of an electric/hydraulic pump as used in a hydraulic-over-hydraulic brake system.

Answer 19

The EH pump supplies a lower pressure to the booster when the power steering pump is unable to maintain high pressure. If the power steering pump fails totally or the engine quits the EH pump takes over to provide partial power braking.

Question 20

Provide a basic hydraulic fluid path between the major system components in a hydraulic-over-hydraulic brake system.

Answer 20

Power steering pump to brake booster to steering gear to pump reservoir; or, power steering pump to steering gear to brake booster to pump reservoir.

Question 21

True or False: Contaminated hydraulic fluid in a hydraulic-over-hydraulic brake system only affects the brake booster.

Answer 21

False; Hydraulic fluid is also used in the power steering pump

Question 22

If a visual inspection of the external components in the hydraulic system does not reveal any problems, what would be the next step in the troubleshooting process?

Answer 22

Relieve system pressure. Install appropriate pressure test instruments. Use manufacturer’s test instructions. Compare readings to specifications. Relieve system pressure before removing test equipment.

Question 23

Explain how to relieve the hydraulic system pressure in a hydraulic-over-hydraulic brake system. What other safety precaution should be followed?

Answer 23

Apply and release the brakes several times. Wear eye protection. Crack a line to relieve residual pressure.

Question 24

Electrical and electronic components are becoming more common on brake systems. Describe some of the typical faults that can cause erratic or inaccurate electrical signals.

Answer 24

Loose, corroded and damaged electrical connectors, and broken, frayed and damaged conductors are the most common problem areas.

Question 25

A vehicle equipped with sensors, computer(s) and electronic modules requires extra care during troubleshooting. Describe the type of information the manufacturer may provide to assist the technician.

Answer 25

Manufacturers provide diagnostic flow charts, wiring schematics, connector and pin descriptions and component location charts. A step-by-step troubleshooting sequence must be followed.

Question 26

Explain the precautions required when testing electrical and electronic circuits and components.

Answer 26

Do not short or ground electrical connections unless it is a part of a recommended test procedure. Use proper test equipment. Confirm electrical pin locations before probing with a test instrument.

Question 27

True or False: Valve bodies that have deep scores can be honed and reused.

Answer 27

False; Deep scores usually mean a new valve body assembly is required.