Driveline and Brakes

if a truck air system is functioning properly, what should be the maximum time required to build system pressure from 85psi to 100psi
how often should truck air tanks be drained during normal operation
daily
when performing a reservoir leakage test, what is considered a maximum acceptable air loss rate for a tractor/trailer combination vehicle
an air compressor fails to build to system pressure within an acceptable time period. What could not be a possible cause of the problem
if the air compressor does not have an intake adapter, how often is it recommended that you should service its air cleaner filter element
which of the following would be more likely to cause an air compressor to cycle frequently and build air pressure slowly
discharge valves leaking
how often should a typical air dryer in a linehaul truck be overhauled
partially restricted oil drain ports in the compressor mounting flange
what would be the more likely cause of compressor pumping excessive oil into the discharge circuit tanks
what values must governor cutout pressure be set within according to FMVSS-121 requirements
115 psi to 135psi
the governor cutout pressure is around 8psi lower than specification on a truck tested during a PMI. What adjustment needs to be made to the governor
 turn governor adjusting screw CCW 1/2 turn, then retest
if a truck air compressor cutout pressure is specified at 125 psi, what must the governor cut-in pressure range be
what should be done when you dispose of failed spring rake chambers
what angle should be formed between a brake chamber pushrod and the centerline of a slack adjuster when S-cam brakes are fully applied
90 degrees
what type of lubricant is recommended for an S-cam profile and rollers
none
what is current industry practice for reconditioning 16.5 inch brake drums that are visibly scored and heat checked
replace with new drums
tech a says that to increase governor cut-out pressure, the jam nut should be released and the adjusting screw turned CW tech b says that turning a governor adjusting screw CW increases the governor spring pressure
when the differential between governor cut-in and cut-out pressure is less than 20 psi what is the probable result
increased compressor cycling frequency
where does the governor sense air pressure
if there is air leakage in the governor unloader circuit what will more likely be the result
frequent compressor cycling
tech a says that a truck with an FMVSS-121 air system must have a minimum of three air reservoirs. tech b says that some FMvSS 121 compliant trucks use a single tank, divided internally into three reservoirs
what test is commonly used by enforcement officers to quickly verify that a truck air sypply system is performing to fmvss121 standards
air build-up from 85 psi to 100 psi
tech a says that most truck compressors today are seldom rebuilt in the field today. tech b says that in most cases it is cost effective to rebuild compressors in the shop rather than stock rebuilt/exchange units’
tech a only
who is responsible for defining OOS criteria on highway trucks
CVSA
you are replacing a spring brake chamber on a truck drive axle with a one with a pushrod that must be cut to size. what must be performed properly fit the new spring brake chamber
assuming major air leak in tractor trailer combination that will result in complete system air pressure loss, which would sequence of events will occur first
dirt build-up around service treadle
what conditions would be most likely to cause brakes not to completely release
tech a says that a frozen relay valve supplying the tractor drive axle brakes can cause service brakes not to apply
both a and b
tech a says that the most accurate way to verify brake shoe to drum clearance is to perform a wheel-down brake adjustment. tech b says that performing a wheel-up brake adjustments can identify problems such as drum warpage as well as set the shoe to drum clearance
tech b only
replace the brake shoes on both ends of the affected axle
when a wheel seal fails and saturates a shoe type brake what should be performed
what descriptions of pneumatic abs is correct?
where s a pulse wheel generator used in a truck abs
when some truck abs circuits are first energized what is the reason for the sequence of clicking noises
solenoids actuating during the start-up self-test
when a tandem axle truck is equipped with 6S/4M split configuration how are the brakes on the drive axles modulated during abs braking
what term has the same meaning as reluctor wheel
exciter ring
what best describes how power line carrier (plc) multiplexing takes place from a trailer to a tractor
what abs configurations is most commonly used on tandem drive highway tractors today
tech a says that trailer abs fault codes are stored in the controller ecu volatile memory. tech b says that abs fault codes can usually be displayed at the controller ecu
read fault codes, troubleshoot both brake and abs failures and analyze brake performance
what does software such as Bendix ACom allow the technician to perform on an abs circuit
tech a says that when an electronic braking system ebs is used on an air brake system, the control circuit is pneumatic and the actuator circuit is electronic-over-electric. tech b says that when ebs is used at this moment in time in North America it is required to have full fmvss121 redundancy
tech b only
tech a says that dual-actuate wedge brakes have better mechanical braking efficiencies than comparable S-ca, actuated brakes. tech b says that dual-actuated wedge brakes tend to require less servicing than comparable S-cam actuated brakes
tech a only
if a spring brake assembly has 90 psi acting on the hold-off dia phragm and no air pressure acting on the serice diaphragm how much linear force is delivered to the slack adjuster
none
both a and b, before attempting to remove and replace it, when making a brake adjustment
when should you cage a spring brake chamber
maintained at60psi, regulated at 90 psi
which of the following is true of hold-off pressure in current truck and trailer air brake system
8 times total brake chamber volume
what is the minimum compressed air reservoir volume dedicated to the air brakes required by an fmvss121 compliant highway trailer
adjust brake free stroke asfriction surfaces wear
what is true of an automatic slack adjuster
require increased stopping distance
aerodynamictractor trailer rigs should have what effect on vehicle braking
150 psi
what pressure is a pop-off valve set to trip at in most highway truck application
trailer swing
when under severe braking the wheels of a trailer lock causing it to spin around while the tractor remains in a straight aead positionthe condition is known as
500 lb-ft
when 1000 pounds of linear force is delivered to a 6-inch slack adjuster how much brake torque is produced at the s-camshaft
heat
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
compressed air
what is the potential energy of an air brake system
primary only
a driver is bringing a tractor trakiler combination to a gradual stop using the trailer service brakes only. a vehicle cuts hi off and he reacts by hitting the treadle valve with panic stop force. what source circuit supplies the trailer service signal from the tractor at the time of the panic applicaiton
resistance of service application pressure versus foot pressure
what factors best account for brake feel in an air brake system
115 psi to 135psi
what pressure value ranges are fmvss 121 compliant cutin and cut out pressures
coefficient of friction
what term is used to measure the aggressiveness of friction facing
spring brake would apply on the affected wheel
what would occur if all of the air leaked out of one hold-off chamber while a vehicle was moving down the highway
300lbs
if a service chamber of a 30/ spring brake chanber has an application pressure of 50 psi acting on its service diaphragm how much linear force is delivered to the slack adjuster
times total brake chamber volume
what is the minimum compressed air reservoir bolume dedicated to the air brakes required by an fmvss121
balance the braking on the tractor and the trailer
what is the reason for using different relay valve crack pressures in a tractor trailer sei combination
remote controlled service brake valve
what is the primary function of the relay valve
speeds up release time
what is the function of a quick release valve when used in a front service brake circuit
trailer swing
when under severe braking the wheels of a trailer lock causing it to spin around while the tractor remains in a straight-ahead position
500 lb-ft
when 1000 pounds of linear force is delivered to a 6-inch slack adjuster how much torque is produced at the s-camshaft
heat
given that energy forms can only altered not eliminated bymechanical action, what is the energy of motion ultimately converted to by a vehicle brake system
compressed air
what is the potential energy of an air brake system
primary only
a driver is bringing a tractor-trailer combination to a gradual stop using the trailer service bakes only. a vehicle cuts him off and he reacts by hitting the treadle valve with panic stop force what source circuit supplies the trailer service
resistance of service application pressure versus foot pressure
what factors best accounts for brake feel in an air brake system
115-135 psio
what pressure value ranges are fmvss 121 compliant governor cut out pressure
coefficient of friction
what term is used to measure the aggressiveness of friction facing
riding the s-cam profiles
in an s-cam foundation brake where would you find brake shoe rollers
tech a only
tech a says that an inversion valve only plays a role when a rig has suffered a significant loss of air. tech b says that the inversion valve acts as an accumulator to provide additional air for emergency braking
16.5 inch
what is the most common brake drum nominal dimension used on heavy duty trucks
disc brakes
what would be more likely to meet the fmvss 121 2010 shorter stopping distance
mechanical spring and pneumatic service application forces
what are the compounded forces that an anti-compounding valve limits
s cam actuated air wedge actuated and air disc brakes
whay type of foundation brakes are used on air-brake equipped trucks and trailers
supply primary and secondary tanks
if a truck is fmvss 121 compliant what air reservoirs must be incorporated into the air brake circuit
preddure protects the tractor air supply in the event of loss of pressure in a trailer, routes trailer supply air and service application signal to the trailer pneumatic circuits and blocks service signal air to the trailer until trailer air supply is activated
what best describes the functions of a tractor protection valve (tp)
governor
if you have to make an adjustment to air system cut out pressure where should the adjustment be ade
tech a only
tech a says that a closed anchor brake shoe web encloses the anchor pin it pivots on tech b says that most current truck s cam brake systems use closed anchor brake shoes
250 feet or less
what is the current required stopping distance for an fmvss 121 compliant tractor trailer semi combination rig
both a and b
tech a says that most air brake system safety pop ff valves trip open at 150 psi tech b says that a safety pop off valve should be fitted to the system supply tank
wedge brakes
what type of heavy truck foundation brakes can be actuated by a power screw
only when new
in current practice in a truck service facilities when should a truck brake drum be machined
maximum service brake pressure
when s cam brakes are properly adjusted , what conditions will result in the most service brake torque
foot valve dual circuit application valve and service brake valve
what terms are used to describe an air brake treadle valve on a fmvss 121 compliant highway truck