Deck 28: Truck Brake Systems

Question 1

What is the primary function of a relay valve?

A) remote controlled service brake valve
B) relays pressure from the primary circuit to the secondary circuit
C) relays governor signal pressure to the unloader pistons
D) routes hold-off air to the hold-off chambers

Answer 1

A

Question 2

An air brake equipped highway tractor features single dash air pressure gauge with two needles,one green and the other red.What does the red needle display?

A) service brake application pressure
B) primary circuit pressure
C) secondary circuit pressure
D) hold-off pressure

Answer 2

C

Question 3

If you have to make an adjustment to air system cut-out pressure,where should the adjustment be made?

A) governor
B) unloader valve
C) dryer purge valve
D) pressure protection valve

Answer 3

A

Question 4

Which of the following pressure values are FMVSS-121 compliant for governor cut-out and cut-in pressures?

A) cut-out at 135 psi and cut-in at 115 psi
B) cut-out at 135 psi and cut-in at 90 psi
C) cut-out at 110 psi and cut-in at 80 psi
D) cut-out at 115 psi and cut-in at 85 psi

Question 5

In a truck air brake system,which sub-circuit is primarily responsible for actuating front axle service brakes when the system is functioning normally?

A) primary circuit
B) secondary circuit
C) supply circuit
D) wet circuit

Question 6

When the emergency/parking brakes are released on an air-brake equipped highway tractor-trailer combination with a three valve system,which dash control button(s)MUST be depressed before you can move the rig?

A) system park only
B) trailer supply
C) tractor park
D) all of the above

Question 7

When a truck has no air pressure in its tanks,which warning devices are activated when the ignition key is turned on?

A) a buzzer
B) red light
C) a dash gauge
D) all of the above

Question 8

In a typical FMVSS 121 compliant tractor-trailer,when you actuate the trailer hand control valve which circuit supplies air to the trailer service brakes when the system is functioning normally?

A) primary circuit
B) secondary circuit
C) supply circuit
D) park/emergency circuit

Question 9

Which types of foundation brakes are used on air-brake equipped trucks and trailers?

A) S-cam-actuated
B) air disc brakes
C) air wedge-actuated
D) all of the above

Question 10

When a FMVSS-121 compliant tractor-trailer is running down a highway and the driver applies the service brakes,which of the following is true at the time of the brake application?

A) only the service application circuit is charged with air
B) only the hold-off circuit is charged is charged with air
C) both service application and hold-off circuits are charged with air
D) hold-off circuit is exhausted and service application circuit is charged with air

Question 11

If a truck is FMVSS 121 compliant,which of the following air reservoirs must be incorporated into the air brake circuit?

A) wet tank and purge tanks
B) front brake and rear brake tanks
C) supply,primary,and secondary tanks
D) wet tank,supply tank,and air start tanks

Question 12

Which of the following are function(s)of slack adjusters used on truck air brake systems?

A) multiply force applied to the S-cams
B) define shoe to drum freeplay
C) convert linear force to rotational force
D) all of the above

Question 13

In what year was FMVSS 121 introduced?

A) 1997
B) 1998
C) 1975
D) 1957

Question 14

What legislation mandates every required standard of a highway truck air brake system?

A) OSHA
B) FMVSS 105
C) FMVSS 121
D) NHTSA

Question 15

How is the relay (secondary)section of an FMVSS-121 compliant dual-circuit foot valve actuated when the air brake circuit is functioning properly?

A) pneumatically
B) mechanically
C) both mechanically and pneumatically
D) by foot pressure alone

Question 16

What is the function of a quick-release gladhand when used?

A) easier to couple and uncouple than a polarized gladhand
B) speeds service brake release timing
C) speeds hold-off air dump at park
D) pressure protects the hold-off circuit

Question 17

When a FMVSS-121 compliant tractor-trailer combination is moving down the highway at a speed of 50 mph,which of the following circuits MUST be charged with air?

A) service brake circuit
B) primary circuit
C) secondary circuit
D) hold-off circuit

Question 18

Which of the following service application valves is sometimes referred to by truck drivers as a trolley valve or spike?

A) trailer hand valve
B) trailer supply valve
C) foot valve
D) treadle valve

Question 19

Which of the following best describes the functions of a tractor protection valve (TP)?

A) pressure protects the tractor air supply in the event of loss of pressure in a trailer
B) routes trailer supply air and service application signal to the trailer pneumatic circuits
C) blocks service signal air to the trailer until trailer air supply is activated
D) all of the above

Question 20

Which valves on a current FMVSS-121 compliant highway tractor are used to balance front and rear braking force under varying operating conditions?

A) quick release and relay valves
B) automatic ratio and bobtail proportioning valves
C) manually-switched front axle limiting valves
D) relay and inversion valves

Question 21

A system air pressure loss occurs on a trailer resulting in a gradual pressure bleed down.Which of the following will occur FIRST?

A) service brakes on trailer apply
B) tractor-protection valve cuts service signal to the trailer
C) tractor-protection valve cuts the trailer supply
D) spring brakes on trailer begin to apply when pressure drops to 60 psi

Question 22

What is the potential energy of an air brake system?

A) the mechanical force applied to the treadle valve by a driver's boot
B) the volume of air contained in all air reservoirs combined
C) a combination of pneumatic and mechanical force applied to the foundation brakes
D) compressed air

Question 23

Which of the following pressure value ranges are FMVSS-121 compliant governor cut-out pressures?

A) 60 - 90 psi
B) 90 - 115 psi
C) 115 - 135 psi
D) 120 - 150 psi

Question 24

Which of the following factors can affect the timing of service brakes?

A) relay valve crack pressures
B) hose and tubing diameters and length
C) replacing a 45-degree fitting with a 90-degree fitting
D) all of the above

Question 25

Which of the following type of heavy truck foundation brakes can be actuated by a power screw?

A) S-cam drum brakes
B) wedge brakes
C) disc brakes
D) driveline brakes

Question 26

A driver is bringing a tractor-trailer combination to a gradual stop using the trailer service brakes only.A vehicle cuts him off and he reacts by hitting the treadle valve with panic stop force.Which source circuit supplies the trailer service signal from the tractor at the time of the panic application?

A) primary only
B) secondary only
C) both primary and secondary
D) trailer onboard supply

Question 27

What governor cut-out pressure is recommended by the ATA (American Trucking Association)TMC (Technology and Maintenance Council)for highway trucks?

A) 115 psi
B) 120 psi
C) 125 psi
D) 130 psi

Question 28

When should you cage a spring brake chamber?

A) before attempting to remove and replace it
B) when making a brake adjustment
C) before performing a chassis lubrication
D) both A and B

Question 29

What is the minimum compressed air reservoir volume dedicated to the air brakes required by an FMVSS-121 compliant highway tractor?

A) 4 times total brake chamber volume
B) 8 times total brake chamber volume
C) 12 times total brake chamber volume
D) 24 times total brake chamber volume

Question 30

Which of the following terms is often used to describe a truck safety pressure relief valve?

A) emergency relay valve
B) quick release valve
C) pop-off valve
D) inversion valve

Question 31

What pressure is a pop-off valve set to trip at in most highway truck applications?

A) governor cut-out pressure
B) governor cut-in pressure
C) 125 psi
D) 150 psi

Question 32

When a tractor spring brake assembly is charged with air on both its service and hold-off chambers,what results is known as:

A) service braking only
B) park braking only
C) compounding
D) proportioning

Question 33

What is the most common brake drum nominal dimension used on heavy-duty trucks?

A) 16.5-inch
B) 18.5-inch
C) 18-inch
D) 19.5-inch

Question 34

What is the minimum compressed air reservoir volume dedicated to the air brakes required by an FMVSS-121 compliant highway trailer?

A) 4 times total brake chamber volume
B) 8 times total brake chamber volume
C) 12 times total brake chamber volume
D) 24 times total brake chamber volume

Question 35

Technician A says that in the event of a total failure of the primary circuit in an FMVSS-121 compliant tractor-trailer combination,the rig is designed to be brought safely to a complete stop.Technician B says that in the event of a total failure of the primary circuit the relay section of the treadle valve will be actuated mechanically.Who is correct?

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

Question 36

When an inversion valve is activated,which of the following occurs?

A) some hold-off air is exhausted
B) service air is dumped
C) tractor protection valve closes
D) park/emergency circuit brakes are fully applied

Question 37

Technician A says that for an air brake system to be FMVSS-121 compliant,there must be a minimum of 3 air reservoirs on a truck.Technician B says that some OEMs use a single air tank,divided into 3 separate chambers each with its own dump valve to meet FMVSS-121 requirements.Who is correct?

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

Question 38

Which of the following factors best accounts for brake feel in an air brake system?

A) resistance of foot valve spring force versus foot pressure
B) actual system pressure at the moment of application
C) relative strength or weakness of the driver's boot
D) resistance of service application pressure versus foot pressure

Question 39

Which of the following is true of hold-off pressure in current truck and trailer air brake systems?

A) maintained at 60 psi
B) regulated at 90 psi
C) subject to chassis system pressure
D) dumped when service brake is applied

Question 40

Technician A says that current air brake systems are designed to bring a fully loaded tractor trailer combination safely to a complete standstill in the event of a complete failure of either the primary or secondary circuits.Technician B says that in an emergency,a tractor-trailer combination can be driven a few miles providing only the secondary circuit has failed.Who is correct?

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

Question 41

A multiple trailer train combination consisting of a tractor and two trailers is spec'd to haul close to maximum loads.Throughout axles in the rig,where would you find the lowest relay valve crack pressures if the rig is spec'd for balanced braking?

A) rear axles on the pup trailer
B) rear axles on the lead trailer
C) tractor drive axles
D) tractor steer axle

Question 42

Technician A says that most current highway tractors use a 3-line TP valve.Technician B says that a 2-line TP valve will remain OFF (closed)until the trailer air supply dash button is depressed.Who is correct?

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

Question 43

In current practice in a truck service facilities,when should a truck brake drum be machined?

A) when heat checked
B) when heat discolored
C) when scored
D) only when new

Question 44

What term is used to measure the aggressiveness of friction facings?

A) inertia resistance
B) coefficient of friction
C) frictional tribology
D) kinetic resistance

Question 45

If the service chamber of a 30/30 spring brake chamber has an application pressure of 50 psi acting on its service diaphragm,how much linear force is delivered to the slack adjuster?

A) 150 lbs
B) 300 lbs
C) 1500 lbs
D) 3000 lbs

Question 46

When a properly functioning treadle valve is actuated by foot pressure,which of the following will determine what pressure is metered out to actuate the primary and secondary service circuits?

A) mechanical force applied to the treadle
B) actual travel of the primary piston
C) actual system pressure at the time of the application
D) mechanical force applied to the relay piston

Question 47

What is the maximum permitted service oversize dimension permitted for a standard 16.5 inch brake drum?

A) 0.060-inch
B) 0.090-inch
C) 0.120-inch
D) 0.180-inch

Question 48

Technician A says that the relay section of a dual circuit foot valve is actuated mechanically under normal operation.Technician B says that the primary piston of a foot valve is actuated mechanically under normal operation.Who is correct?

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

Question 49

Technician A says that a relay piston in a foot valve responds to pneumatic signal from the primary section of the valve,by metering out into the secondary circuit the same pressure that acts on it.Technician B says that the further a primary piston travels through its stroke in a dual circuit foot valve,the more pressure is applied in opposition to foot pressure.Who is correct?

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

Question 50

Where should grease be applied on an S-cam brake system components?

A) S-cam profile contact face
B) cam roller contact face
C) cam roller pocket race
D) all of the above

Question 51

Technician A says that truck brake shoe edge codes are used as an exact measure of their coefficient of friction.Technician B says that the first letter of an edge code indicates the coefficient of friction of the friction facing when cold.Who is correct?

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

Question 52

How many anchor pins are used for a pair of S-cam actuated brake shoes?

A) one
B) two
C) four
D) eight

Question 53

Technician A says that a trailer service brake signal is always sourced from the tractor primary circuit.Technician B says that a trailer service signal can only pass through a tractor protection (TP)valve when it is in its ON state.Who is correct?

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

Question 54

Technician A says that dual-actuated wedge brakes have better mechanical braking efficiencies than comparable S-cam actuated brakes.Technician B says that dual-actuated wedge brakes tend to require less servicing than comparable S-cam actuated brakes.Who is correct?

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

Question 55

Technician A says that when air is charged to a trailer with a spring brake priority system,it is directed to the hold-off chambers of the spring brakes BEFORE the reservoirs are charged.Technician B says that when a trailer is equipped with a spring brake priority system the air tanks must be fully charged with air before the parking brakes can be released.Who is correct?

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

Question 56

In an S-cam foundation brake,where would you find brake shoe rollers?

A) riding the S-cam profiles
B) on the shoe anchor
C) S-cam bushings
D) return spring clips

Question 57

Technician A says that a closed-anchor brake shoe web encloses the anchor pin it pivots on.Technician B says that most current truck S-cam brake systems use closed-anchor brake shoes.Who is correct?

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

Question 58

Technician A says that air disc brakes have higher mechanical braking efficiencies than S-cam actuated,drum brakes.Technician B says that air disc brakes offer better control than equivalent drum brakes.Who is correct?

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

Question 59

What are S-cam type foundation brakes mounted to?

A) axle spindle
B) brake drum
C) wheel hub
D) spider

Question 60

Given that energy forms can only be altered not eliminated by mechanical action,what is the energy of motion ultimately converted to by a vehicle brake system?

A) brake dust
B) sound
C) kinetic energy
D) heat

Question 61

Which of the following best describes the role of an air compressor?

A) a motor
B) an engine
C) an air pump
D) an air cleaner

Question 62

Which of the following correctly describes the function of an automatic slack adjuster?

A) converts linear force to torque
B) acts as a lever to increase mechanical advantage
C) resets brake free stroke as friction linings wear
D) all of the above

Question 63

What is primarily used to cool air compressors on most truck air brake systems?

A) engine coolant
B) water
C) ram air
D) alcohol injection

Question 64

When a driver is using the trailer hand brake valve to stop a rig and then stomps on the treadle valve,what is the source of the trailer service control signal?

A) tractor primary circuit
B) tractor secondary circuit
C) trailer reservoirs
D) trailer hold-off circuit

Question 65

Aerodynamic tractor-trailer rigs should have what effect on vehicle braking?

A) Make the rig easier to stop
B) Require increased stopping distance
C) Should not influence braking
D) Influence braking only at low speeds

Question 66

How many supply tanks would a typical tractor-trailer semi-combination rig be equipped with?

A) one for the entire rig
B) one for the tractor,one for the trailer
C) one for each drive axle
D) one for each trailing axle

Question 67

What would occur if all of the air leaked out of one hold-off chamber while a vehicle was moving down the highway?

A) service brakes would apply on the affected wheel
B) service brakes would apply on the whole rig
C) spring brake would apply on the affected wheel
D) parking brakes would apply on the whole rig

Question 68

When under severe braking,the wheels of a trailer lock causing it to spin around while the tractor remains in a straight-ahead position,the condition is known as:

A) jackknife
B) trailer swing
C) plow-out
D) brake fade

Question 69

Technician A says that most air brake system safety pop-off valves trip open at 150 psi.Technician B says that a safety pop-off valve should be fitted to the system supply tank.Who is correct?

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

Question 70

When the governor routes air to the compressor unloader circuit,what happens?

A) the compressor drive disconnects
B) the compressor intake valves are held open
C) system air pressure is at its lowest
D) all of the above

Question 71

When S-cam brakes are properly adjusted,which of the following conditions will result in the most service brake torque?

A) highest pressure in hold-off chambers
B) maximum service brake pressure
C) highest vehicle road speed
D) shortest distance from the brake treadle valve

Question 72

Which of the following terms is used to describe an air brake treadle valve on a CMVSS 121 compliant highway tractor?

A) foot valve
B) service brake valve
C) dual circuit application valve
D) all of the above

Question 73

Which of the following is true of an automatic slack adjuster?

A) signals driver when brakes need adjusting
B) automatically defines the amount of brake force required
C) automatically sets the amount of hold-off chamber force
D) adjusts brake free stroke as friction surfaces wear

Question 74

Which of the following components functions to control the compressor effective cycles?

A) treadle valve
B) safety pop-off valve
C) inversion valve
D) governor

Question 75

Technician A says that brake chambers convert air pressure into rotary force.Technician B says that slack adjusters convert rotary force into linear force.Who is correct?

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

Question 76

Technician A says that Rockwell automatic slack adjusters generally use stroke-sensing adjustment on the release stroke.Technician B says that Gunnite slack adjusters use clearance-sensing adjustment on the apply stroke.Who is correct?

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

Question 77

Technician A says that automatic slack adjusters are required to be fitted to all currently manufactured highway tractors and trailers.Technician B says that it is recommended that an automatic slack adjuster is not adjusted after being put in service.Who is correct?

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

Question 78

What is the function of the compressor on a truck air brake system?

A) compress ambient air
B) clean ambient air
C) dry ambient air
D) all of the above

Question 79

If a spring brake assembly has 90 psi acting on the hold-off diaphragm and no air pressure acting on the service diaphragm,how much linear force is delivered to the slack adjuster?

A) 2000 pounds
B) 200 pound
C) 1800 pounds
D) none

Question 80

When 1000 pounds of linear force is delivered to a 6-inch slack adjuster,how much brake torque is produced at the S-camshaft?

A) 50 lb-ft
B) 100 lb-ft
C) 500 lb-ft
D) 1000 lb-ft