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

Question 1

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

A) hydraulic pressure actuates the hydraulic booster assemblies
B) hydraulic fluid flows through the quick release valves
C) modulated air pressure actuates pneumatic booster assemblies
D) modulated hydraulic pressure actuates the pneumatic booster assemblies

Answer 1

C

Question 2

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

A) delays application of front disc brakes
B) reduces rear wheel lock-up
C) alerts the driver to a partial circuit hydraulic failure
D) all of the above

Answer 2

D

Question 3

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

A) crocus cloth
B) cylinder hone
C) emery paper and a wooden dowel
D) none of the above

Answer 3

D

Question 4

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

A) a hydraulic brake pedal acts as a lever to multiply force
B) application force is multiplied hydraulically by the wheel cylinders
C) actual braking force at the wheels correlates with the mechanical force input at the pedal
D) all of the above

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?

A) the brake system ECU
B) the rear drums
C) ABS sensor
D) brake pedal

Question 6

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

A) power steering pump
B) dedicated hydraulic pump
C) reserve electric motor and pump
D) all of the above

Question 7

What does the term hygroscopic mean?

A) designed to absorb moisture
B) designed to resist moisture absorption
C) designed to act as a hydraulic medium
D) designed to resist expansion when subjected to temperature rise

Question 8

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

A) allow it to settle first in a clear container to check for contaminants
B) filter through a strainer to remove particles
C) boil it to remove all moisture
D) never attempt to reuse any used brake fluid

Question 9

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

A) alerts the driver to a partial system hydraulic failure
B) ensures brakes are prioritized over the power steering requirement for brake fluid
C) alerts the driver to a partial system mechanical failure
D) all of the above

Question 10

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

A) dual hydraulic circuits
B) mechanical parking brakes
C) mechanical emergency brake
D) all of the above

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?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

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?

A) leading shoe
B) trailing shoe
C) both shoes
D) neither shoe

Question 13

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

A) pressure differential valve
B) metering valve
C) proportioning valve
D) load proportioning valve

Question 14

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

A) pressure differential valve
B) proportioning valve
C) metering valve
D) all of the above

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?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 16

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

A) open the bleed nut and drain the displaced fluid
B) open the master cylinder lid to allow the fluid to return to the reservoir
C) either A or B
D) neither A nor B

Question 17

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

A) pressure bleeder
B) maximum air system pressure
C) allow the system to self-bleed
D) any of the above

Question 18

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

A) micrometer
B) dial indicator
C) digital calipers
D) micrometer with a Vernier scale

Question 19

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

A) canister-spring brake
B) driveline mounted drum brake
C) cable and lever actuated secondary shoe
D) driveline-mounted,lever-actuated disc brake

Question 20

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

A) primary piston is actuated mechanically
B) secondary piston is actuated hydraulically
C) there is a single bore
D) all of the above

Question 21

Technician A says that most current truck hydraulic brake systems use single-acting wheel cylinders.Technician B says that in a double-acting wheel cylinder,a pair of pistons are actuated from a single bore,and act on both brake shoes.Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 22

Technician A says that ABS hydraulic brake systems should be bled using a bleeder ball.Technician B says that a bleeder ball regulates output air pressure at approximately 15 psi.Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 23

Technician A says that drum servo brakes are self-energizing.Technician B says that servo brakes both primary and secondary shoes play a role in braking the drum whether the vehicle is moving forward or in reverse.Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 24

When honing a cast iron master cylinder,what should be used to lubricate the hone?

A) diesel fuel
B) engine oil
C) solvent
D) brake fluid

Question 25

Which of the following types of power boosters are used in light and medium-duty truck brake systems?

A) vacuum boosters
B) hydraulic boosters
C) pneumatic boosters
D) all of the above

Question 26

What is the primary cause of disc brake rotor warpage?

A) excessive brake pressure
B) over-heating
C) operation in wet conditions
D) panic brake stops

Question 27

You are measuring the axial TIR of a hydraulic brake rotor and through one revolution you measure +0.003-inch and -0.006-inch.What is the TIR?

A) 0.003-inch
B) 0.006-inch
C) 0.009-inch
D) 0.018-inch

Question 28

Technician A says that in a servo-type hydraulic drum brake,each shoe is separately anchored at its heel.Technician B says that in a non-servo type brake system,the trailing shoe is only energized when the vehicle is travelling in reverse.Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 29

Technician A says that excessive rotor runout on hydraulic brake systems can result in brake pedal pulsation.Technician B says that excessive rotor runout can cause decreased pedal travel.Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B

Question 30

Technician A says that contaminants tend to collect in the caliper bore of a hydraulic disc brake system so the piston should never be forced back into its bore without cracking the bleed screw.Technician B says that ABS hydraulic brake systems are more vulnerable to problems caused by contaminants in brake fluid.Who is correct?

A) Technician A only
B) Technician B only
C) Both A and B
D) Neither A nor B