Deck 31: Air Brake Servicing

Question 1

What should be done when you dispose of failed spring brake chambers?

A) cage the mainspring and dispose of in scrap metal bin
B) disarm in a disarmament chamber then dispose of in scrap metal bin
C) cage and dispose of in a landfill site
D) call a hazardous waste recycler

Answer 1

B

Question 2

Which of the following would be more likely to cause an air compressor to cycle frequently and build air pressure slowly?

A) alcohol evaporator empty
B) discharge valves leaking
C) rings passing oil
D) all of the above

Answer 2

B

Question 3

Which of the following would NOT be justification for tagging a vehicle in OOS (Out Of Service)?

A) audible air leak from any brake chamber
B) brake chamber pushrod stroke less than 1 1/2" (38 mm)on any drive axle
C) service brake hose that bulges when under pressure
D) mismatched slack adjuster lengths on the steer axle

Answer 3

B

Question 4

How often should truck air tanks be drained during normal operation?

A) daily
B) weekly
C) at each PM service
D) monthly

Question 5

What type of lubricant is recommended for an S-cam profile and rollers?

A) lithium-soap grease
B) anti-seize compound
C) API GL-5 lube
D) none

Question 6

Which of the following would be the more likely cause of a compressor pumping excessive oil into the discharge circuit tanks?

A) partially restricted oil drain ports in the compressor mounting flange
B) failed or empty alcohol evaporator canister
C) defective governor
D) all of the above

Question 7

What is the maximum permissable free-stroke limit for a clamp-type,size 30,long-stroke brake chamber?

A) 2 inches (50 mm)
B) 2 1/4 inches (57 mm)
C) 2 1/2 inches (64 mm)
D) 2 3/8 inches (61 mm)

Question 8

What is current industry practice for reconditioning 16.5-inch (420 mm)brake drums that are visibly scored and heat checked?

A) machine to 0.120" (3 mm)oversize
B) replace with new drums
C) skim until smooth providing oversize does not exceed 0.180-inch (4.5 mm)
D) dedicate for use on trailers only

Question 9

What values MUST governor cutout pressure be set within according to FMVSS-121 requirements?

A) 90 and 115 psi (6.2 - 7.9 bar)
B) 100 and 125 psi (6.9 - 8.6 bar)
C) 115 and 135 psi (7.9 - 9.3 bar)
D) 125 and 150 psi (8.6 - 10.3 bar)

Question 10

What angle should be formed between a brake chamber pushrod and the centerline of a slack adjuster when S-cam brakes are fully applied?

A) 90 degrees
B) just under 90 degrees
C) just over 45 degrees
D) 45 degrees

Question 11

An air compressor fails to build to system pressure within an acceptable time period.Which of the following could NOT be a possible cause of the problem?

A) worn compressor compression rings
B) compressor inlet restriction
C) compressor discharge port restriction
D) ruptured service diaphragm

Question 12

What is the usual maximum cam-to-bushing radial play permissable in an S-cam assembly?

A) .010-inch (0.25 mm)
B) .020-inch (0.50 mm)
C) .030-inch (0.75 mm)
D) .050-inch (1.27 mm)

Question 13

How often should a typical air dryer in a linehaul truck be overhauled?

A) 300,000 miles (483,000 km)or every 3 years,whichever comes the soonest
B) 100,000 miles (160,000 km)or every year,whichever comes the soonest
C) 50,000 miles (80,000 km)or every 6-months whichever comes the soonest
D) they are service-rated for the life of the vehicle

Question 14

The governor cutout pressure is around 8 psi lower than specification on a truck tested during a PMI.Which of the following adjustments would be more likely to correct the cutout pressure?

A) turn governor adjusting screw CCW 1/2 turn,then retest
B) turn governor adjusting screw CW 1/2 turn,then retest
C) turn governor adjusting screw CCW one full turn,then retest
D) turn governor adjusting screw CW one turn,then retest

Question 15

Air continuously leaks from the exhaust port of a tractor relay valve when the park brakes are released.What should be done?

A) repair the exhaust valve
B) replace the relay valve
C) check the related spring brake chambers for hold-off pressure back-flow
D) replace the park/emergency quick-release valve

Question 16

If the air compressor does not have an intake adapter,how often is it recommended that you should service its air cleaner filter element?

A) every 5,000 miles (8,000 km)
B) every C-level PMI
C) once a year
D) daily

Question 17

If a post-2010 truck air system is functioning to the FMVSS 121 standard,what should be the maximum time required to build system pressure from 85 psi to 100 psi (5.8 to 7 bar)?

A) 25 seconds
B) 40 seconds
C) 60 seconds
D) 90 seconds

Question 18

When performing a reservoir leakage test,what is considered a maximum acceptable air loss rate for a tractor/trailer combination vehicle?

A) 6 psi (40 kPa)in 2 minutes
B) 6 psi (40 kPa)in 1 minute
C) 2 psi (14 kPa)in 2 minutes
D) 2 psi (14 kPa)in 1 minute

Question 19

If a truck air compressor cutout pressure is specified at 125 psi,what must the governor cut-in pressure range be?

A) 85 - 100 psi (5.8 - 7 bar)
B) 95 - 115 psi (6.6 - 7.9 bar)
C) 100 - 105 psi (7 - 7.2 bar)
D) 110 - 120 psi (7.6 - 8.3 bar)

Question 20

You test governor cut-out pressure to be exactly at specification but governor cut-in is too low.What should you do FIRST?

A) raise to specification adjusting the governor
B) check the operation of the unloader circuit
C) replace the governor
D) replace the compressor

Question 21

When using a spring disarmament chamber to disarm a spring brake,specifically what must be cut with an oxy-acetylene torch before you open the chamber after the procedure?

A) spring chamber band clamp
B) service chamber band clamp
C) main spring
D) service spring

Question 22

Technician A says that to increase governor cut-out pressure,the jam nut should be released and the adjusting screw turned CW.Technician B says that turning a governor adjusting screw CW increases the governor spring pressure.Who is correct?

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

Question 23

Assuming a major air leak in tractor-trailer combination that will result in complete system air pressure loss,which of the following sequence of events will occur FIRST?

A) trailer supply button pops out
B) tractor protection valve trips to OFF
C) spring brakes start to apply when hold-off air drops below 60 psi (4 bar)
D) tractor inversion valve actuates

Question 24

When the differential between governor cut-out and cut-in pressures is less than 20 psi,which of the following will more probably result?

A) extended intervals between compressor effective cycles
B) lower than specified system pressures
C) increased compressor cycling frequency
D) unloader valve failure

Question 25

When you are using visual stroke indicators to assess slack adjuster stroke,which of the following is required?

A) system air must be at system pressure
B) parking brake released,wheels chocked
C) observe as service brakes are applied
D) all of the above

Question 26

What is the typical service life of an air dryer desiccant cartridge?

A) 3 months
B) 1 year
C) 2 years
D) 3 years

Question 27

A truck driver complains that air is being discharged from somewhere in the supply circuit at a frequency of every minute or so: there is no evidence of continuous air leakage on the truck.Which of the following should be checked out first?

A) compressor inlet restriction
B) leakage in the unloader circuit
C) defective alcohol evaporator
D) defective air dryer purge valve

Question 28

Who is responsible for defining OOS criteria on highway trucks?

A) OSHA
B) FMVSS
C) CVSA
D) ATA

Question 29

Technician A says that most truck compressors today are seldom rebuilt in the field today.Technician B says that it most cases it is cost effective to rebuild compressors in the shop rather than stock rebuilt/exchange units.Who is correct?

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

Question 30

You are replacing a spring brake chamber on a truck drive axle with a one with a pushrod that must be cut to size.Which of the following MUST be performed to properly fit the new spring brake chamber?

A) replace the pushrod clevis yoke
B) replace the slack adjuster
C) cut the pushrod to size to ensure 90-degree fully-applied slack adjuster angle
D) cut the spring brake bracket to ensure 90-degree pushrod to slack adjuster angle

Question 31

If a truck brake system is functioning properly,when should the low air pressure warnings (buzzer and light)be illuminated

A) pressure drops below governor cut-out
B) pressure drops below governor cut-in
C) pressure drops to between 70-60 psi (4.8 - 4.1 bar)
D) pressure drops to tractor protection valve trip-out pressure

Question 32

Technician A says that if the electrical supply to an air dryer is interrupted,the dryer purge valve will immediately cease to function.Technician B says that the heater used in many air dryers is cycled by a thermostat.Who is correct?

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

Question 33

Which of the following tests is commonly used by roadside enforcement officers to quickly verify that a truck air supply system is performing to CVSA standards?

A) air build-up from 0-60 psi (0-4 bar)
B) air build-up from 85-100 psi (5.8-6.9 bar)
C) air build-up from 100-120 psi (6.9-8.3 bar)
D) air build-up from 105 psi (7.2 bar)to governor cutout psi

Question 34

What brake diagnostic tool is used to measure the change in angle of a truck chassis when it is subjected to aggressive braking?

A) duplex air gauges
B) decelerometer
C) inclinometer
D) protractor and level

Question 35

Technician A says that most modern friction facings used on truck drum brake shoes are much softer than the asbestos facings used a generation ago.Technician B says that a disadvantage of modern friction facings is that they destroy brake drums at a much faster rate than asbestos facings.Who is correct?

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

Question 36

Technician A says that a truck with an FMVSS-121 air system must have a minimum of three air reservoirs.Technician B says that some FMVSS-121 compliant trucks use a single tank,divided internally into three reservoirs.Who is correct?

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

Question 37

Where does the governor sense air pressure?

A) supply tank
B) primary tank
C) compressor discharge
D) air dryer

Question 38

When you are installing open anchor brake shoes (such as Q-brakes)which of the following steps should be performed first?

A) install the retraction spring
B) install the lower brake shoe and anchor springs
C) install the upper brake shoe
D) install the axle spindle,sleeve wear sleeve

Question 39

Technician A says that when you observe excessive slack adjuster pushrod travel,the slack adjuster is probably over-adjusting.Technician B says that an over-adjusting slack adjuster must be replaced.Who is correct?

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

Question 40

If there is air leakage in the governor unloader circuit,which of the following will more likely result?

A) high system pressures
B) frequent compressor cycling
C) extended compressor unloaded cycles
D) safety pop-off valve tripping

Question 41

What is the current maximum stopping distance for an FMVSS 121 compliant tractor trailer rig that is unloaded?

A) 216 feet (66 meters)
B) 250 feet (76 meters)
C) 432 feet (132 meters)
D) 500 feet (152 meters)

Question 42

If a trailer service brake combination valve were NOT equipped with an anti-compounding feature,which of the following could compound the brakes?

A) pull trailer supply valve out then fully depress the tractor foot valve
B) apply the trailer hand valve and tractor foot valve simultaneously
C) fully depress the tractor foot valve,then pull trailer supply valve out
D) all of the above

Question 43

When soap-solution testing the operation of an FMVSS-121 treadle valve,what is the maximum permissable leakage at the exhaust valve during an 80 psi (5.5 bar)service application?

A) absolute zero
B) 1-inch (25 mm)bubble in 3-seconds
C) 1-inch (25 mm)bubble in 10-seconds
D) 1-inch (25mm)bubble in 60-seconds

Question 44

What is the current FMVSS 121 maximum stopping distance for a fully loaded tractor trailer combination traveling at 60 mph (97 kph)?

A) 216 feet (66 meters)
B) 250 feet (76 meters)
C) 432 feet (132 meters)
D) 500 feet (152 meters)

Question 45

Technician A says that when testing the performance of a dual circuit foot valve,it is normal to measure about 2 psi (14 kPa)higher pressure in the outbound primary circuit than in the outbound secondary circuit.Technician B says that warped trailer air disc brake rotors can cause foot valve chatter during service applications.Who is correct?

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

Question 46

The power spring in a spring brake chamber unit:

A) should never be tampered with
B) should be replaced at C-inspections
C) imparts more force than a full service air application
D) all of the above

Question 47

Technician A says that before checking rotor runout on a truck equipped with air disc brakes,the wheel bearings must be verified to be properly adjusted.Technician A says that rotor thickness is measured with a dial indicator.Who is correct?

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

Question 48

Technician A says that when a supply reservoir is completely drained,air pressure in the primary circuit should drop to zero.Technician B says that when the secondary reservoir is completely drained,pressure in the primary reservoir should drop to zero.Who is correct?

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

Question 49

How fast are the wheels turned on a diagnostic brake dynamometer?

A) 0 mph (0 kph)
B) 1 mph (1.5 kph)
C) 40 mph (64 kph)
D) 55 mph (90 kph)

Question 50

Technician A says that polarized gladhands are used to prevent cross-coupling of the trailer supply and service hoses.Technician B says that a quick release gladhand produces faster emergency brake application on the trailer in the event of a breakaway.Who is correct?

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

Question 51

Technician A says that a common cause of parking brakes that will not hold,is out of adjustment slack adjusters.Technician B says that loss of pressure in the secondary circuit can cause poor trailer parking brake performance.Who is correct?

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

Question 52

Technician A says that a frozen relay valve supplying the tractor drive axle brakes can cause the brakes not to release.Technician B says that a frozen relay valve can cause service brakes not to apply.Who is correct?

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

Question 53

When a wheel seal fails and saturates a shoe type brake,which of the following should be performed?

A) wipe the oil off the friction facings with petroleum solvent
B) pressure wash the shoes and spider assembly
C) replace the brake shoes on the affected brake
D) replace the brake shoes on both ends of the affected axle

Question 54

How could a driver determine the air pressure in the secondary circuit?

A) low air pressure warning switch
B) check the secondary pressure gauge needle
C) check the primary circuit gauge needle and subtract from system pressure
D) check the actuation pressure gauge needle

Question 55

When an ABS equipped tractor is coupled to a non-ABS trailer,which of the following would likely result from a panic service brake application?

A) tractor front axle brake lock-up
B) tractor drive axle brake lock-up
C) all tractor brakes lock-up
D) all trailer brakes lock-up

Question 56

Which of the following conditions would be most likely to cause brakes not to completely release?

A) leakage at the trailer service gladhand
B) excessive slack adjuster stroke
C) dirt build-up around service foot brake
D) leakage at a service diaphragm