Clutch Fundamentals and Service

function and operating principle

  • function of spring-loaded clutch
    • connect drive and driven unit
    • transmit power during engagement process
    • disengage engine from transmission
  • springs
    • diaphragm
    • angled
    • perpendicular
  • types
    • push-type
    • pull-type
      • have clutch brake
      • adjustable
  • size of the clutch determined by
    • dia of the disc
    • OD of the clutch shaft
    • number of splines in the hub
    • number of dampening springs
  • actuation
    • mechanical
    • hydraulic
    • air or air-over-hydraulic (used air to boost hydraulic pressure)

components

  • flywheel
    • pilot bearing is used to pilot the transmission input shaft, center clutch disc in relation with pressure plate
    • flat
      • clutch cover/pressure plate is fastened to the outer dia of the flywheel
    • countersunk
      • have a recessed friction surface
      • clutch cover/pressure plate is fastened to the raised outer dia section
  • clutch cover
    • stamped steel
      • lighter allow higher engine speed
    • cast iron
      • absorb more heat
      • high torque load
  • clutch discs
    • lining bonded or riveted
    • dampened clutch discs: designed to absorb torsional vibrations
    • rigid clutch discs
    • do not use grease or oil based (varsol) to clean lining
  • lining
    • organic or non-asbestos organic (NAO)
    • ceramic for heavy application
  • intermediate plate
    • used to increase friction area, thus increasing torque loads
    • drive pins/plugs splines to drive slots on flywheel/clutch cover
      • should be loose to prevent clutch discs from remain in contact with a friction surface
      • anti-rattle springs located bw them slot to reduce noise and vibration during engagement and disengagement
  • clutch levers
    • used to move pressure plate closer to the clutch cover
  • release bearing
    • used to move the clutch release levers and minimize wear of release levers during the engagement or disengagement process
    • push-type: bearing only spin during the engagement and disengagement process
    • pull-type: bearing rotate all the time when engine is running
      • bearing operates under load during the engagement and disengagement process
  • drive and driven members
    • drive member: flywheel, clutch cover, pressure plate, intermediate plate
    • driven member: clutch discs
  • clutch adjustment
    • disc lining, flywheel, and pressure plate wear, the free travel is lost
    • manual
      • push-type: adjust @ threaded push rod
      • pull-type: adjust internal threaded ring
    • self-adjustment
      • auto compensate for wears
    • adjusting clutch too tightly leads to premature wear of release bearing and release lever
  • clutch brake
    • used to stop the rotation of the clutch disc and transmission input shaft on shifting from neutral to first or reverse
    • pull-type
      • 2 solid fiber clutch discs are positioned on on either side of the steel clutch plate
      • one-piece clutch or torque-limiting clutch brakes will slip above a pre-determined torque load
      • 2 piece clutch brake allows easier installation and removal

service

  • service clutch
    • inspect internal clutch components through inspection opening
    • adjust clutch
      • turning adjusting ring clockwise moves the release bearing toward the clutch
      • clutch wear, need to move pressure plate closer to the flywheel
    • lubricate release bearing
    • inspect fastener for looseness
    • operate vehicle within its normal load and speed will extend service life
    • disconnect battery ground cable to prevent start is accidentally engaged
    • use long guide stud on removing clutch cover/pressure plate
    • aligning shaft used to help control clutch discs as the clutch is removed
    • only adjust clutch free play when checking all linkage for wear
  • faults
    • operator related problems
      • pedal to the floor @ any gear selection, causing clutch brake engaged under heavy load, premature wear
    • slipping, causing heat
      • oil seal leaks, contaminating clutch discs
      • start in too high gear
      • heat
        • causes lost of spring tension, reduce clamping force
        • can explode
    • dragging
      • clutch is not quick freed from flywheel once the clutch pedal has been depressed
      • cause difficult to shift because clutch is partially connected to flywheel
      • improper clutch adjustment
        • too little free play
          • release bearing and release levers could be in constant contact, causing bearing premature wear as it’s running under load all time
        • excessive free play
          • reduce the amount of remaining pedal movement available to disengage clutch
          • cause fail to completely disengage the clutch (clutch drag)
    • chattering
      • wear in external components, e.i. loose engine mounts
      • worn clutch discs splines, trans input shaft splines, warped friction surfaces
      • oil leak causes lining glazed, worn in an unusual patterns cause chattering
    • vibration
      • mud, debris picked up by rotation member
      • loose and separated lining
    • warpage
      • clutch working under extreme load causes heat which causes warpage of flywheel, pressure plate, intermediate plate
      • machine to fix if within limit
      • measure by straight edge and feeler gauge
  • pressure spring inspection
    • squareness
    • height
    • tensions @ specific height
  • crankshaft end play
    • do several time to ensure all of the oil film has been squeezed out
  • flywheel face run-out
  • flywheel pilot bearing bore run-out
  • outer flywheel bore run-out
  • flywheel housing bore run-out
  • flywheel housing face run-out
  • clutch housing face run-out
  • clutch housing bore run-out (may use an adapter lever to help read)
  • 4-step torque process: 1/3, 2/3, full torque, recheck full torque

no-pedal clutch system

  • standard style clutch is the most common design
  • use with turbine when warm-up period is necessary
  • 2 forces react when clutch engaged
    • centrifugal force
    • friction force
  • @ full load speed, the clutch is in lock position

driveline fundamentals

  • func of driveline
    • transmit power
    • allow angle changes
    • allow length changes
  • driveline is too long will tend to flex and increase load on joints
    • driveline length will depend on torque, speed, dia of the tube
  • center support bearing or midship bearing used to carry the weight of the first shaft, and secure its position
  • use safety guards/shields place around rotating assemblies
  • drive-line tube
    • bend cause vibration
    • overload cause damage to the tube
    • 2 checks
      • runout
      • balance (by weld weight to the tube weld weight to the tube))
  • universal joints
    • a trunnion, a highly polished bearing surface
    • bearing strap requires locking compound
  • yoke
    • welded (tube yokes)
    • slip yokes (sleeve)
      • phasing
      • allow change in length
  • shaft arrangement
    • parallel shaft arrangement, drive unit input and driven unit output shaft are parallel
      • max working angle 1 degree
    • broken-back or intersecting angle: center lines extends and intersect over the middle of the driveline
  • faults
    • spalling: overload
    • galling: lack of lub, incorrect working angle
    • brinelling: u joints is operated at zero degree working angle, or lack of lub
    • pitting: contaminated lub
    • seized bearing caps or split joints causes vibration
    • misalignment of the axle housing forces ujoints work at greater angles
  • vibration free
    • phasing
      • correct phasing is to ensure that 2 ujoints on each driveline assembly are correctly aligned with each other
        • measure phase by a bubble level
          • out of phase caused by twisted shaft
    • balance
    • working angles
      • rules
        1. ujoint working angle must be at least 1 degree which helps to provide lub for trunnions
        2. working angle of ujoint on opposite ends of each individual drive line must be within 1 degree of each other
        3. max drive line working angle should be less than 3 degree for high speed operation
      • single plan: side view or top only
      • compound: consider top and side view
  • vibration
    • low speed vibration: wheel/wheel bearing fault
    • higher pitches sound and vibration will be in driveshaft
      • noise present during increase and decrease speed
    • vibration cause broken sychronizer pins or fretted clutching teeth
  • when the shaft speed is higher, the working angle must be less

Transmission Fundamentals

  • function
    • multiply torque
    • reverse
    • neutral
  • choose transmission based on
    • engine peak torque (high or low torque)
    • rpm range (broad or short range)
      • large range: use large ratio step bw gears
      • short range: smaller ratio change bw gears
    • applications
      • carry light load, short distance, low speed: van truck (hino)
      • pull heavy load, long distance, high speed (tractor)
      • carry and pull load (commercial bus)
      • extreme heavy load, low speed
  • transmission front
    • transmission input shaft, clutch shaft
    • transmission input shaft gear, transmission drive gear or main drive gear
      • the gear can be integrated to clutch shaft or separated
      • separated gear can have windback seal system to eliminate the need of lip seal
    • bearing retainer cover holds the bearing and input shaft assembly in position
      • have shim to adjust for end play and preload for input shaft bearing (tapered)
      • have oil seal, gasket
  • countershaft
    • one-piece
    • multiple pieces
    • 1st, 2nd counter shaft drive gears, etc.
    • countershaft gears constant mesh with mainshaft gears
    • each countershaft has different pto gears, same for others
  • main shaft and main shaft gears
    • none of main shaft gears connected to the main shaft
    • mainshaft gears will be temporarily connected to the mainshaft through a synchronizer assembly (not first and reverse gear)
  • reverse idler
    • constant in mesh with countershaft and mainshaft reverse gear
  • synchronizer
    • func
      • use to synchronize speed of mainshaft gear with mainshaft during shifting process
      • temporarily connect mainshaft and mainshaft gears
    • synchro action
      • hub is spline to the shaft, shift collar sync hub and main shaft gears
      • block synchro
        • tappered area of blocker ring contacts tapered portion of the mainshaft gear to sync speed of mainshaft and mainshaft gear
          • shift yoke force overcomes spring pressure holding the inserts
        • serration on the blocker ring cone surface allow oil film exist during sync
      • pin type synchro
        • sync pin is tapered to prevent shift collar move to quickly to the mainshaft gear
          • normal spring
          • split pin to provide spring-loaded resistance
        • cone surface on mainshaft gears is serrated for oil film
        • blocker can be coned or bevel, same for clutch collar
      • plate and disc synchronizers
        • drum (hub) splines to shaft (act like shift collar)
  • shift lever
    • used to transmit the actions of the operator to the shift fork and rails
    • isolator reduces transmission noise from being transmitted up into the cab
  • shift rails and forks
    • move sliding clutch
    • have oil trough to direct oil to critical transmission parts
  • detents
    • spring loaded
    • help to hold shift rail in position
  • spring-loaded plunger
    • use for first/reverse shift block
    • give operator conscious indication of shifting first or rev gear
  • interlocks
    • prevent selecting more than 1 gear at a time
  • multiple countershaft
    • handle high torque
    • use smaller lighter housing, bearing, countershaft,etc.
    • mainshaft gears float bw countershaft gears: counteract axial thrust, no need for mainshaft bearings
    • double tooth contact area, so narrow down teeth width
  • override transmission: (fifth gear is override)
  • direct transmission: (fifth gear is direct)

Aux section

  • range: large ratio change
  • splitter: small ratio change
  • deep reduction: provide lower starting gear
    • used sliding clutch
    • used in three-speed aux
  • aux drive gear
    • splines to mainshaft or float bw 2 aux countershafts
  • countershaft
    • helical gear
    • tapered roller bearing
  • synchronizer
    • range shift
  • range, splitter, deep reduction assemblies
    • o-rings prevents air one side of the piston to other or into the transmission
  • output shaft
    • deliver torque to driveline
    • a speedometer drive gear is on the output shaft (cable system)
    • tooth or tone ring/wheel (electronic speedometer)
  • forward: front trans
  • rearward: back trans
  • two speed aux section
    • provide reduction and direct
  • spin-on filter
    • cooler -> inlet -> trans -> outlet -> filter -> cooler
  • three speed aux section
    • 15-speed, but 12 usable gears
    • deep reduction (low-low): only low range can have deep reduction
      • shift pin-type synchro rearward
      • shifting deep reduction sliding clutch rearward
    • low range
      • engage LO gear by
        • shifting pin type synchro rearward
        • shifting deep reduction sliding clutch forward
    • high range
      • engage HI gear by
        • shifting pin-type synchro forward
        • shifting deep reduction sliding clutch forward
  • four speed aux section
    • low, low
      • pin-type clutch: rearward
      • sliding clutch: forward
    • low, high
      • pin-type clutch: rearward
      • sliding clutch: rearward
    • high, low
      • pin-type clutch: forward
      • sliding clutch: forward
    • high, high
      • pin-type clutch: forward
      • sliding clutch: rearward
  • transmission lub
    • splash type
      • galleries and oil trough help direct oil
        • for critical area, synchronizer, aux drive gear bearing
    • pressure type
      • eccentric, shutter type oil pump
      • help coil transmission
    • filtration
      • magnetic drain plugs

Hybrid drive

  • mild hybrid
    • provide acc assist
    • e.i garbage truck
  • full hybrid
    • acc assit & propel
    • e.i electric hybrid city deliver truck
  • architecture
    • series
      • engine drives generator charging bat & driving wheel motors
      • never direct power the vehicle
      • e.i haul truck
    • parallel
      • electric motor or hydraulic pump is sandwiched bw engine and trans
      • either of them or both of them drive trans
  • motor/generator
    • propel vehicle
    • charge the high voltage batteries during deceleration
  • inverter
    • convert 340V dc to 340V ac
    • during regeneratie braking convert 340V ac to 340V dc charge batteries
  • PEC - power electronics carrier
    • 340V lithium batteries
    • relay
    • connectors
  • propulsion:
    • electric only
    • diesel electric (lower engine duty cycle, better gas consumption)
    • diesel
  • charging:
    • during braking or coasting
  • benefits
    • fewer emission, better fuel economy
    • 120V ac receptacles without running engines
    • use motor to start engine, don’t use starter, thus reducing wear on it
    • electric PTO
  • diesel hydraulic hybrid
    • hydraulic launch assist (HLA)
    • pump/motor
      • charge accumulator during coast or regenerative braking
      • be a motor to apply torque to the driveline
    • active when
      • 5-35km
      • enough oil
      • enough acc pressure
      • cruise is off
      • no faults
  • coasting:
    • HLA assist in slowing vehicle when operators release accelerator
  • regenerative braking
    • releasing accelerator will trigger regenerative braking
    • transfer case disengage, stop regen when accumulator is fully charge
    • the rising pressure in accumulator resist the forward motion, causing slow down
  • gloves
    • rubber in, leather out (top)
    • the higher glove glass number, the higher voltage can withstand
  • high voltage cable is ORANGE
  • wait 5 minutes for high pressure oil in acc depressurized

Transmission shifting

  • air filter/regulator
    • first component receive air supplied
    • act as a filter
    • regulate about 58-63psi
  • slave valve
    • allow preselect range shift
    • receive supply air from filter/regulator
    • low range, master valve send air to slave valve, move piston to the left (low-air-piston-move- right)
    • high range, air exh from master valve
    • shift lever is in neutral, actuating pin moves away from slave valve
  • master air control valve
    • receive supplied air from slave valve
    • red: 13 (low range, low split only), blue 15, grey 18
    • send air signal to slave valve or cylinders
    • vent air from cylinder in master valve
  • range cylinder
    • 30-40% gear ratio
    • double cylinder
    • piston go to right: low range (master valve sends air)
    • piston go to left: high range
  • splitter cylinder
    • 15-20%
    • constantly receive air from filter/regulator on rod side
    • piston go to the left: low split (master valve releases air) (air both side, base end wins)
    • piston go to the right: high split (signal air sent to spliter)
  • lines and fittings
    • 1/4” rubber supply lines
    • 1/8” plastic control lines
    • S - supply (red)
    • P - pilot (black)
    • H/L - splitter or deep reduction (green)
    • SP - splitter pilot
  • semi-automated transmissions
    • top 2 gears (most use on road) are automatically selected
    • monitor
      • transmission output shaft speed
      • engine speed
      • throttle position
    • engine electronic control unit controls the shift system
  • electronic shift control (shift-by-wire)
    • X-Y shifter
      • rail motor is a reversible DC motor
      • motor move the shift finger along the shift shaft to the shift rail though a slotted connection bw rail nut & shift finger
    • inertia brake
      • located on PTO opening (connect directly to main countershaft)
      • aid shifting process help slow down main countershaft and then the aux input shaft
    • range-shifter motor
      • used electric-over-air solenoids
    • shift controller
      • electronic control unit (transmission controller)
      • operator shift console (drive, neutral, etc.)
    • in hold mode, operator can manually control upshift and downshift
    • in low mode, operator get maximum engine braking

Transmission service

  • oil leak
    • worn seal, loose fasteners
    • plugged breather
    • incorrect oil
  • slip out
    • occur when the torque is applied (accelerating, decelerating)
    • sliding clutches have back tapper (dovetail) to help keeping gear from slip out
    • transmission mount eccentric
    • worn mainshaft/output shaft bearing
    • shorten clutching teeth due to excessive gear clashing
    • weak or broken detent springs
    • wear on detent notch of the shift rail
    • incorrect adjustment of linkage
  • jump out
    • occur in normal condition or rough road condition
    • heavy & long shift levers
    • weak or broken detent springs
    • excessive movement bw the transmission and the shift linkage
  • hard shift
    • external
      • binding shift linkage
      • lack of lub
    • internal
      • twisted mainshaft
      • broken mainshaft key
      • reverse spring-loaded plunger
  • gear clashing
    • worn input shaft splines that do not let the clutch fully release, causes gear clashing in reverse and first
    • excessive clutch free play causes clutch not fully release and drag
  • noise
    • whine or squeal
      • insufficient clearance or backlash
    • growling
      • broken teeth
      • improper timing
      • incorrect installation of the counter shaft gears
  • overheating
    • exceed 120C or 250F, oil loses lubrication properties
    • transmission @ an excessive angle
    • coasting downhill with clutch depressed or improper towing cause lack of lub
  • gear wear
    • frosting (middle) and offset frosting (side): OK
      • result from the mating gears wearing
    • healing OK
      • after frosting, the area is shinny
    • gear pitting
      • replacement based on size and depth of pitting hole
      • is it local or stretched?
      • can cause noise
    • spalling (replaced)
      • similar pitting, but larger area, and shallower depth
      • overload
    • scoring/galling (replaced)
      • lack of lub, high temp cause welding occur
    • burned (replaced)
      • blue area
      • lack of lub
      • lack of clearance (middle of gears outwards)
    • impact fractures (replaced)
      • shock loading
      • foreign object passing to gear mesh
    • fatigue fractures (replaced)
      • beach marks
    • stringers/gas pockets (replaced)
  • air system diagnosis
    • slow/no shift
    • chassis air pressure must be 90psi for testing
  • electric hybrid system diagnosis
    • create buffer zone 1m around equipment with cones
    • verify glove before each use
    • gloves should not have any holes
    • leather outside, rubber inside gloves
  • hydraulic hybrid system diagnosis
    • turn off ignition, wait 5 minutes for depressurized accumulator

Transfer case and aux drive

  • transfer case receive torque from transmission then passed that torque to rear and front driving axles
  • lub by splash or pressure
  • types
    • two shaft, single speed, full time all wheel drive (can not disengage front drive shaft)
    • four shaft, two speed, neutral, PTO, (ability to disengage front drive shaft)
  • front axle declutch
    • disengage the torque to the front drive axle
    • good for highway application
  • high range: direct
  • low range: reduction
  • proportional differential and lockout
    • used planetary gear set to prevent driveline windup
      • input: PC - main drive shaft
      • output
        • sun: front axle (30%)
        • ring: rear axle (70%)
      • reactionary: traction
    • loose traction on all the output, zero torque! need to lock 2 member carrier and the sun
  • PTO on 2 speed transfer case, engage only in neutral
    • can overspeed PTO if trans is placed in high gear
  • clean pto components with petroleum-based, DO NOT use steam cleaning and soapy water
  • assembly
    • need end play, NOT preload
  • PTO
    • front-mounted
    • rear-mounted (need a special flywheel housing)
    • transfer-case-mouted (more torque)
    • drop box
      • large amount of torque
      • transfer power to PTO and 1 drive axle only
      • PTO runs, power to drive axle is interrupted
      • commonly direct drive
    • aux transmission top mounted PTO
    • SAE classifies 2 types of mounting PTO: 6 or 8 bolt size
    • actuation methods
      • cable
      • mechanical
      • air
        • pressure protection valve is mounted before air valve
      • electric
    • a gasket is used bw PTO and transmission to
      • seal lubrication from transmission
      • adjust PTO backlash (0.006” [compressed 10 thou shim] - 0.012” [compressed 20 thou shim] backlash)
      • filler block is used if need more than four gaskets
      • adapter plate: 6bolt to 8 bolts at least 1 seal for each adaptive surfaces
      • adapter housing: used when transmission has obstruction like exhaust system
        • has a idler which needs to check backlash with countershaft and PTO
    • operator must stop the transmission countershaft from turing before engaging the PTO
    • indicator light is activated by an engagement switch located on the shift cover

Drive axle assembly fundamentals

  • GAWR - gross axle weight rating
    • the amount of weight each axle can safely carry
  • GVWR - gross vehicle weight rating
    • adding all GAWR
  • GCWR - gross combination weight rating
    • combined weight of tractor, trailers, and loads
  • func of drive axle
    • support weight and load of vehicle
    • change direction 90 degree
    • multiply torque
    • allow diff action
  • add a driving axle to increase traction
  • add a non-driving axle to increase flotation
  • differential ratio chosen factors
    • startability
      • % of grade at which a drivetrain system can start a loaded vehicle moving at an idle
    • fuel economy
  • carrier housing
    • hold internal gear components, e.i. pinion gear, bevel gear, diff case, diff assembly, diff lock
    • cast iron
    • external or integral housing
  • pinion cage house tapered pinion bearing
  • drive pinion
    • overhung: flat surface on the top of pinion
    • straddle: stub shaft extended on the top of pinion
      • amboid (top), hyroid (bottom)
  • thrust screw and jam nut
    • prevent bevel gear from deflecting away from pinion during high torque load
    • position opposite the bevel gear & pinion mesh, installed on carrier housing
  • configurations
    • single speed, single reduction (@ bevel gear)
    • single speed, double reduction (@ bevel and helical gear
    • two speed, double reduction
      • 2 helical spur gear, 2 helical bull gear for 2 speed
      • sliding clutch for choosing between 2 helical gear sets
    • planetary, two speed
      • low speed
        • sliding clutch engages low speed clutch plate (bearing adjuster)
        • input: ring gear (bevel gear)
        • held: sun splines with bearing adjuster (sun shift outwards)
        • out: pc (diff case)
      • high speed
        • sliding clutch engages high speed clutch plate (PC)
        • sun is locked with PC, direct drive
  • differential actions
    • torque is divided equally
    • each wheel speed = bevel gear speed / 2
    • lost traction 1 wheel (e.i free spin)
      • torque is low because of loss of traction
      • torque is delivered equal both wheel
      • the wheel has traction receive torque required to rotate the wheel with poor traction
        • can be stopped
      • whatever speed is lost on one side is gained on free-spin wheel
  • diff lock
    • lock one axle shaft to diff case
  • inter-axle differential assembly
    • send torque to both driving axles
    • cross shaft has internal splines
    • allow diff speed bw forward and rearward drive axle
    • power flow
      • input shaft
      • cross shaft, or spider, or inter-axle diff assembly, [or diff [cross] shaft]
      • diff pinion
        • helical drive gear (replace side axel gear which mesh with diff pinion, has lockout gear)
          • helical driven gear
          • pinion (input shaft of front drive axle)
          • bevel gear
        • side gear
          • output shaft
          • output yoke
    • only lock out diff while the truck is moving straight-ahead at a low speed
      • lock input shaft and helical drive gear
  • semi-floating axle
    • drive axle assembly
    • handle driving, braking, cornering, load force!
  • full-floating axle
    • only drive the wheel and hub assembly
    • weight vehicle transmit to axle housing, bearing, hub assembly
  • outboard planetary final drive
    • ring is held by splined to spindle
    • input: sun
    • output: pc (hub assembly)
  • drive axle lub
    • splash
    • splash and pressure
      • oil pump is mounted in front of diff carrier to ensure it always runs in any cases regardless of any spinning wheels
      • inter-axle diff is mounted top, may starve of lub, specially in wheel spin condition where front differential is NOT spinning
    • filter
      • spin-on filter
      • magnetic drain plug
      • magnetic screen on the oil pickup
  • no-spin traction control
    • normally engage diff lock, wheels run same speed
    • unlock diff when the outer wheel is overrun the inner wheel
    • ratcheting noise will occor during the cornering process which is normal
  • driver controlled diff lock
    • spring release, air applied

Drive axle assembly service

  • when drive axle operates at an angle of over 12, a standpipe should be used
  • gaskets are NOT used bw housing, it uses RTV sealant
  • check end play of both input and output shaft
    • can cause vibration of it is out of specs
  • perform plug swap, inspecting the contamination on the plug
  • lose suspension components can cause noise
  • mismatch tires cause excessive heat and wear due to continuous diff action
  • noise on drive
    • loose, worn bearings
    • low/wrong lubrication level
    • excessive backlash, end play
  • noise on coast
    • pinion and ring gear to tight
  • intermittent noise
    • warped ring gear
    • loose diff case bolts
  • constant noise
    • flat spot on bearing, gears
    • bent axle shaft
    • worn pinion splines
  • lub
    • oil temp should not exceed 250F or 121C
    • after fill drive axle assembly with correct amount of lub, drive the truck for few minutes, then shutdown 5 minutes to recheck the oil level, top up if needed
    • low oil level causes overheat, losing oil film quality
    • high oil level causes foaming, reducing oil film quality
    • if oil is contaminated, wheel end assemblies must be removed, the hubs cleaned, and bearing inspected
  • pre-disassemble check: backlash in case the axle has to be reused
    • measure at 4 evenly positions on the ring gear
  • assembly differential
    1. pinion bearing preload: apply press load while checking rotation torque of pinion
      • use norminal bearing spacer for initial check
    2. tooth contact pattern (adjust pattern can affect backlash, thus, doing the pattern before backlash)
      • use a pry bar to apply load to ring gear on checking pattern
      • move ring affects heel and toe
        • excessive heel: lower pattern, move ring towards pinion
        • excessive toe: moving away from pinion
      • move pinion affect: face and flank (need to readjust backlash)
        • excessive face: move pinion in
        • excessive flank: move pinion out
    3. side bearing preload (backlash)
      • adjusting rings used to adjust bearing preload
      • adjust until end play is eliminated, but backlash bw the pinion and ring gear still exists
      • move ring gear close to pinion, decrease backlash
      • move ring gear further from pinion, increase backlash
    4. pinion depth
      • positive (+) number indicates how much further
      • negative (-) number indicates how much closer
    5. bevel gear run out
    6. thrust screw
      • mark the spot with the most back face runout toward the thrust screw side of the bevel gear
      • thread the thrust screw into the diff carrier until it seats in the thrust block
      • back off 180 degree
      • rotate, make sure that thrust screw does not bind at any location
  • assemble inter-axle differential
    • input shaft end play
      • established with shim bw bearing cage and the housing
  • when selecting particular gear oil, expected working ambient temp must be consider
  • wheel lock must be engaged to remove the carrier assembly from the housing
    • a special bolt threaded into the air fitting port OR
    • apply 80-120psi shop air to the shift cylinder

Steering system

  • connection
    • steering arm
    • pitman arm:
      • change rotation motion to linear motion
      • time bw pitman arm and the sector shaft
    • drag link
      • move in an arc, thus can not be rigid
    • upper steering arm
    • left hand steering knuckle
      • has steering stop
        • need to be adjusted to allow minimum clearance of 1 inch bw the tire and the frame
      • kingpin
        • thrust bearing must be installed UNDER the axle end
    • left hand lower steering arm
    • tie rod
    • right hand lower steering arm
    • right hand steering knuckle
  • steering gear
    • transmit the driver’s intentions from steering wheel to the linkage
    • change direction in the path of power
    • mechanical advantage for steering
  • lock spring
    • allow the steering wheel to rotate in both directions while still having signal and power going to the switches
    • turning the steering wheel while the steering shaft is disconnected could result in damage to the clock spring assembly
  • SRS: supplemental restrain system
    • commonly in yellow wire
    • air bag discharges can easily damage clock spring
  • steering columns
    • tilt steering columns
      • tilt steering columns up and down
      • use additional ujoints and two shafts
    • telescoping steering columns
      • height is adjustable
  • steering gear types
    • manual steering gear
      • recirculating ball design reduces clearance bw the worm shaft and the ball nut, reduce friction, and allow a little play
      • sector shaft gear rotates about 30 degree
    • integral power steering gear common
      • power steering fluid
        • provide lub film
        • cool components
        • seal bw shafts and sealing devices
        • dot NOT mix with engine oil
        • flush the system, when change to new fluid
        • reservoir, pressure relief
          • steering is jammed, operator still pulls on the steering wheels, the valve opens
          • too low, poor assist, hard steering
          • too high, damage linkage
      • poppets release the pressure before contacting steering stop (1/8” in before hit the stops)
      • a torsion bar actuates the valve assembly
      • a rotary valve assembly controls the flow of oil in the steering gear
    • rack and pinion
      • a torsion bar
      • the oil is directed to the rack mounted assist cylinder through external lines
      • no pitman arm, drag link, or an upper control arm

steering service

  • low front tire pressure, dragging brake can seem like a steering problem
  • squealing noise, excessive tire skid
  • clock spring: non serviceable
  • the threaded portions of both drag link ends or tie rod end must be completely inserted into the drag link/tie rod tube
    • wheel must straight ahead when removing clock spring
  • do NOT turn the steering wheel during filling and bleeding to prevent air enter system
  • perf test
    • pressure
    • flow rate
    • do NOT leave load valve on flow meter closed longer than 5 seconds
  • internal leakage
    • use an unhardened steel spacer
    • hold steering wheel contact spacer @ 20lbs
    • max flow rate must not exceed 1gpm
  • poppet setting test
    • hold steering wheel contact stop screw @ 20lbs
    • pressure should be 200-400psi less than pump relief pressure
    • NOT OK
      • pressure does not drop
      • if pressure drop when the steering stop is farther than 1/8”
  • when the vehicles wheel base is lengthened or shortened, it can cause increases in front tie wear due to the increase in tire skidding on turns
  • using the steering wheel as a grab handle can cause the pivot bolts in a tilt steering column to brake
  • the supply and return lines must be removed from the steering gear when draining the system
  • to remove the sector shaft, the worm shaft and the ball nut assembly must be centered
  • when replacing the rack and pinion steering gear, always replace the mounting bolts
  • the steering stops must be set before the drag link is hooked up to prevent automatic poppets being misadjusted
  • turn adjusting screw in to reduce backlash bw sector shaft and the rack piston
  • use inch pound torque wrench to check for valve body bearing preload and the sector shaft

Steering angles and alignment

  • toe: tire wearing angle
    • compensate for any deflection in the steering linkage
    • 2 types: toe in & toe out
    • excessive: feathered edge (direct relationship high edge with in/out)
    • adjust by turning tie rod
  • caster: directional control angle
    • positive caster: top of the steering axis (king pin) tilt towards the rear of vehicle
    • increase the vehicle’s tendency to want to go straight ( help to turn the steering wheel to the straight-ahead position after making a turn)
    • 3 types: positive, zero & negative
    • excessive positive caster
      • good: direct shock load to suspension
      • bad
        • hard steering
        • shimmy: unstable, rapid side-to-side movement
    • excessive negative caster
      • good: easy to steer at low speed
      • bad:
        • instability @ high speed
        • wander and weave: difficulty in maintaining a straight-ahead direction
    • adjusted by placing ONE tapered shim bw the axle and the leaf spring
  • camber: tire wearing and also directional control angle
    • positive: tilt out at the top
    • negative: tilt in at the top
    • make it easy to steer by lowing vehicle’s weight to the steering axis
    • tire wear
    • unequal camber results in a pull to the side that has the most positive camber
    • excessive camber causes premature fail of wheel bearings
    • adjusted by bend axle (not recommended), should replace it
    • high camber reading may indicate a KPI problem to to damaged axle or steering knuckle
  • KPI - king pin inclination (fulfils the same role as camber)
    • can not adjustable
      • adjusted by replacing damaged parts (steering knuckle)
    • directional control (steering stability)
    • reduce the need for high camber
    • reduce shock load
    • include angle = KPI angle + camber angle
    • scrub radius is the distance bw the projected steering axis and the center of the tire contact area, measure at the road surface
  • turning radius is toe-out on turns : tire wearing angle
    • the shape of steering arms determines the angle
      • adjusted by replacing damaged parts (steering arms)
    • help reduce tire scuff
    • front tires turn at diff angles
  • thrust angle
    • is the angle formed by the thrust line and geometric center line (GCL)
      • thrust line determines the direction the vehicle will travel
    • incorrect thrust angle cause vehicle not going straight
    • should check axle housing in relation to the frame rails
  • scrub angle
    • is the angle formed by horizontal lines drawn through the rear axle
    • causes: tires scrub positive or negative
  • vehicle could pull to the side having the smaller tire
  • vehicle tilts towards the low pressure tire
  • loose wheel bearings will affect toe and camber
  • broken and sag springs can affect camber and caster
  • alignment tools: radius plates,caster/camber bubble type alignment gauge

Air ABS

  • func
    • maintain control throughout a braking application (prevent wheel lock)
      • or prevent tire flat spotting if wheels are locked
    • reduce overall stopping distance
  • does not provide extra brake effort
  • configurations
    • 2S/1M minimum on tandem axle trailer
    • 2S/2M common on tandem trailer
    • 4S/4M common on tandem axle power unit (tractor)
    • 6S/6M maximum vehicle control and safety for tri-axle trailer/ normal tractor
  • channels are the number of modulators
  • tone ring, tooth wheel, tooth ring, exciter ring
    • mounted on wheel hub
  • speed sensor
    • permanent magnet
    • held in a spring clip
    • speed increases, both voltage and frequency increase
  • air brake modulator valve
    • normally open, allow free flow of air in normal condition
    • contains 2 solenoids, 2 diaphragm valves (supply and exh solenoids, valves)
      • exhaust, hold, reapply
    • normal braking
      • de-energized supply solenoid moves up, allows supply air unseating supply diaphragm, supply air goes to chamber
      • de-energized exhaust solenoid moves down, allows supply air seating exhaust diaphragm, air from chamber is NOT exhausted
    • exhaust (abs event)
      • energized supply solenoid moves down, allows supply air seating supply diaphragm, supply air is blocked
      • energized exhaust solenoid moves up, allows chamber air unseating exhaust diaphragm, air from chamber is exhausted.
    • holding
      • energized supply solenoids moves downs, blocks supply enter
      • de-energized exhaust solenoid moves down, allows supply air seating exhaust diaphragm, air from chamber is NOT exhausted
    • reapply
      • de-energize both solenoids, return system to normal
  • ECU: inside the cab, baggage compartment, frame, cross member, trailer air reservoir
  • built after March 1, 1998, trailer has abs light on the left rear corner facing outward
    • ABS is mandatory as of March 1, 1998
      • receive power from aux pin
  • as of March 1, 2001, we have abs light in the cab for trailer
  • diagnostic connection
    • usually J-1587
  • off-road ABS sw
    • turn off ABS because we believe that mud, soil, or sand helps vehicle stop
  • tractor/trailer power cord
    • middle top/middle/bottom: ground/aux,keyed,ecu power/stop lamp (backup)
    • under L/R: LH, RH turn/hazard
    • above L/R: clearance/Tail lamp
  • ATC: automatic traction control
    • auto apply brake when foot on accelerator
    • braking a specific wheel
    • reducing the amount of torque delivered to the drive wheels
    • ATC valve
      • located bw brake valve and service relay @ the rear drive axles
      • 3 airlines
        • to brake valve
        • from supply air
        • to air discharge
      • normal condition
        • block supply air
        • allow signal air to relay valve
      • wheel-spin (no brake)
        • block brake valve air
        • open supply air to send signal air to relay
      • differential braking
        • ATC valve send signal air to relay
        • ECU send signal to modulators which control spinning wheels to apply brake
        • ECU send signal to modulators which control non-spinning wheels NOT to apply brake
      • torque reduction
        • engine is electronically controlled
        • used J-1939
    • below 40km/h , use diff braking and torque reduction if wheels are still spinning
    • above 40km/h, use torque reduction only; diff braking causes drive line shock load
    • deep snow and mud option
      • allow wheel spin slightly faster than normal without automatically applying brake to throw off mud and debris to clean the threads, improve traction
    • disable ATC for chassis dynamometer to prevent ATC system from attempting to control the spinning wheels by
      • remove fuse
      • scan tool or PC
      • press on the blink code sw for 3 sec
  • RSC: roll stability control
    • help control vehicle stability and limit rollovers by
      • apply brake on the correct wheels
    • components
      • ATC valve
      • RSC valve
        • located in secondary system bw brake valve and tractor protection valve
      • ATC and RSC share the same indicator lamp
      • depend on speed and lateral movement ecu can signal
        • retarder, engine brake
        • tractor/trailer service brake
        • reduce engine torque
  • ESC: electronic stability control
    • add directional stability to RSC system to help prevent jackknife or spinout
    • components
      • ESC module contains yaw senssor and an accelerometer
        • located in the center of the frame rail
        • measure lateral acceleration
        • communicate with ABS ECU
      • front axle control valve
        • a ATC valve controlling steer axle brakes
      • steering angle sensor (SAS)
        • tell ABS ECU where the operator is attempting to steer to determine jackknife condition
      • brake demand sensor
        • tell ABS ECU how much brake demand pressure to correct the vehicle
  • service
    • first step troubleshooting: speak with the operator, review work order, visual inspect
    • pre-check service brake (ABS rely on service brake)
      • brake adjustment
      • air system
      • condition of mechanical components: linkages, drums, mounting brackets, etc. (most common problems)
    • pre-check ABS
      • connections integrity: electrical cables & connections, speed sensors, etc.
      • physical damage
      • unequal tire size
    • do NOT disconnect/connect ABS cables and components while the system has power
    • push wheel speed sensor contact to tone ring; turning the wheel may establish the proper running clearance
    • tone ring
      • excessive wheel bearing end play will result in erratic wheel speed sensor readings

Hydraulic ABS

  • ABS modulator valve assembly or solenoid control valve assembly
    • prevent wheel lock by decreasing, increasing, main brake pressure
  • DOT5 is silicone-based fluid do NOT use in ABS
  • DOT3 & 4 can be mixed
  • to depressurize ABS may require 30 or more full brake pedal applications
  • 3 types of ABS
    • rear wheel antilock only
    • rear wheel and individual front wheels antilock
    • individual front and rear antilock
  • ABS indicator lights
    • display ABS fault codes
    • bulb checks
    • brake fluid level
  • precheck
    • fluid level
    • battery voltage
    • visible damage
    • vehicle on safety stand

Truck electrical Circuit

  • lighting circuits
    • driver vision
    • driver convenience
    • truck safety
    • truck appearance
  • constant power terminal: connect to bat terminal of the starter
    • head light
      • low beam receive power from constant power terminal
    • tail light: rear dimensions of the back of truck, red
    • brake light
    • clearance light: outside dimensions of the truck, yellow or amber; marker light: upper regions of the truck
      • master lightning sw control clearance/marker lights
    • cab light
      • L/R hand door sw and dash-mounted sw (all open, cab light’s OFF)
    • trailer receptable
    • ignition sw
  • circuit breakers and fuse
    • type 1: constantly automatic restart: head light
    • type 2: not auto restart, internal resistor keeps bimetal from reset until problems are fixed
    • type 3: not auto restart, manual restart with button
  • DRL: daytime running light
    • conform CMVSS 108 (Canadian Motor Vehicle Safety Standard)
  • NRL: night running light
  • control intensity of dash panel light
    • rheostat:
      • connect in series with dash panel light circuit
      • create heat
    • PWM:
      • connect in series with dash panel light circuit
      • minimum waste of energy
      • high accuracy
    • fibre optics
      • if the fibre optics do not illuminate, light source has failed
  • turn signal light and brake light
    • signal and brake light circuits share the same filament
    • turn signal flasher is connect in series with the turn signal light circuit
      • electromechanical
        • can have one extra terminal called pilot terminal, trigger a indicator light circuit
        • LED signal lights do NOT draw enough current to allow an electromechanical flash to operate LED signal lights correctly
      • solid state electronic
        • use with LED turn signal
  • backup light
    • connected ignition switch-controlled circuit which prevent backup light from discharging bat when engine is not running
    • can incorporate a beeper
  • solenoids
    • discrete solenoids: 2 position fully retracted or extended
      • sleeper door latch: solenoid is energized of the door is unlatched
    • proportional solenoid
      • the solenoid’s movement is directly proportional to the voltage applied to the solenoid coil
    • latching solenoid
      • a discrete solenoid that remains fixed at the end of its travel when de-energized
    • self-induction arcing protection: voltage remove -> magnetic field collapses -> create induced voltage
      • install a high value resistor in parallel with solenoid coil
      • install a clamping diode/self-discharge diode in parallel with the solenoid coil
        • block current flow to the ground side
  • programming PTO parameters into the engine ECM to
    • optimize PTO function
    • create a report of PTO time and fuel usage for a tax rebate
  • switches
    • SPST spst
    • SPDT spdt
    • DPDT dpdt
  • dc motor
    • CEMF (counter electromotive force)
    • DC motor speed increases, CEMF increases
    • high starting torque
    • draw more starting current
    • overloaded motor operated @ low speed and generate little CEMF, draw more current, thus generating lots of heat.
    • 2 types:
      • permanent magnet
        • reverse motor by simply changing the polarity of the input power
      • field wound
        • reverse motor by changing electric connection inside the motor
          • add motor reverse switch inside the motor, connecting to field coil
        • parallel wound or shunt motor
          • field coils parallel with armature wiring
          • CEMF generated by armature does NOT affect the current through the field coil
            • stable speed, low starting torque
    • speed control
      • variable electrical resistance
        • use none, 1, 2, etc. resistors
      • multiple shunt windings
        • use shunts with diff diameter field coils
      • PWM
        • the longer the ON time, the faster the motor turn
  • battery isolation switches (BIW) prevent the batteries from discharging while the truck is parked
    • need fuses for accessories that require memory
      • to prevent cranking engine with BIW in open position which will damage the accessories
      • to prevent crank engine with a bad ground
  • install series coil (filter choke) or a parallel-connected capacitor @ the source
  • truck data monitoring
    • collect driver perf: engine rpm, speed, idler hours,etc. by using data logging unit
  • vehicle tracking system
    • GPS
    • communication component: digital satellite uplink
  • truck position sensing
    • CWS - collision warning system: front-end, turn on 15mph or more
    • CMS - collision mitigating system: rear-end, turn on 15mph or more
    • ACC - adaptive cruise control: maintain safe distance
    • use mono-pulse radar sensor: OnGuard (has gyro sensor inside)
  • tire pressure control system
    • low tire pressure can cause overheating (large footprint)
  • potentionmeter controlled system
    • pontentionmeter
    • stepper motor: move up to 255 step in a 360 degree
      • HVAC blend air door
  • windshield wiper/washer control system
    • park contacts located inside the motor assembly
      • supply current to the motor after the wiper sw is turned OFF
        • allow motor continue operating until the wipers reach the park position
  • power inverter
    • convert 12V DC to 110V AC
  • gauges and sending units
    • dicrect acting gauges: do NOT use sending units
      • speedometer: cable to transmission output shaft
      • tachometer: cable to fuel pump or camshaft
    • indirect acting gauges: requires sending units
      • analog gauges
        • balancing coil (electromechanical)
        • stepper motor (PWM)
          • speedometer, tachometer, engine temp, fuel level, etc.
        • air core
          • brushless permanent magnet motor
      • digital gauges
        • sending units:
          • pressure:diaphragm acting, semi-conductor sending unit
          • position or level:variable resistor
            • has a pointer
            • may need an anti-slosh module that minimizes the gauge pointer fluctuation
          • temperature:thermistor
            • a variable resistor based on temperature
            • PTC - positive type coefficient
              • temp increases, resistance increases
            • NTC - negative type coefficient
              • temp increases, resistance decreases
          • amperage:shunt
            • heavy gauge cable connected bw alternator and battery
            • advantage: small cable go to dash gauge unit
          • amperage:hall effect sensor and IC (newest)
          • voltmeter analog
            • display the truck electrical system’s state of charge
          • speed:pulse generator
            • rotating permanent magnetic generator
            • relatance voltage generator (use tone wheel & stationary permanent magnet)
            • PPM - pulses per mile = tire rev per mile x rear axle ratio x tone ring teeth
  • warning lights
    • isolating diodes prevent all the warning lights from illuminating when just one warning light is illuminated
    • alternator warning light is ON if battery is charging
      • alternator generate output, R terminal has voltage
      • first start the key, the light is on
        • later, alternator works charging the battery, we have voltage on R terminal which powers relay coil cause the light off
  • baud rate is the speed of data transfer over the network
    • kilobits per second Kb/s
    • megabits per second Mb/s
  • backbone or data bus is a method of connection
    • class A: twisted pair (less than 10kb/s)
    • class B,C: shielded/unshielded twisted pair, or twisted quad (10kb/s to 1Mb/s)
    • class D like class B, C with fibre optic (1Mb/s-10Mb/s)
  • stub or branch
  • node: a device has address
  • protocol: common langauge for daat communication: J1587 and CAN
    • CAN: controlled area network
      • series communication protocol
      • used on high way truck
    • data links: J1587, J1939; communication bw node and diagnostic tools
  • topology describes logic structure of control modules on the data bus
    • all control module has equal priority
    • priority is encoded into the message
  • multiplexing: send and receive signals bw control modules @ high speed
    • each controller contains a transceiver chip follow CAN protocol
  • MID message identifier - 1byte
    • which components send the error code: engine, transmission, etc.
    • or indicate the source address of the transmitting code:
  • PID parameter identifier - 1byte
    • which parts in the components have problems: engine oil pressure, etc.
    • that parameter the following data corresponds
  • FMI failure mode identifier
    • defines the type of failure
  • PGN parameter group number
    • a unique number assigned to each message
  • SPN suspect parameter number
    • identify where a specific failure occured
  • checksume, verify integrity of message, checksum is zero, the message is valid
  • BHM - bulkhead control module or ESC - electrical system controller
    • control of other electronic modules
    • controls CHM, EXM, SEM, etc.
  • CHM - chassis control module (OEM)
  • EXM - same as CHM, but its aftermarket
  • SEM - addition CHM
  • message corruption is reduced on a J1587/J1708 by using an unshielded twisted wire pair
  • J1939 uses CAN protocol
  • in J1939, voltage diff bw CAN-high and CAN-low determines if an bit is + or -
  • terminating resistors are used to terminate the signal on a J1939 in order to prevent standing waves from occurring
  • testing the J1939/Can data link resistance by checking resistance bw pins C and D for 60ohm

Truck electrical circuit service

starting

  • all electrical SCHEMATICS are drawn in a DE-ENERGIZED condition
  • all the electrical COMPONENTS are drawn in their NORMAL position
  • a relay is drawn arrow point to 87a in de-energized condition, it’s a normally closed relay
  • soldering is NOT recommended for digital circuits
  • splicing multi-strand wire
    • twist wires together or western union splice
    • soldered wires
    • heat shrink tubing applied
  • cimp splice using
    • a butt connector
    • splice clip
  • strip approximately 7.5 mm of insulation from each wire to be spliced
  • alignment headlights address
    • drivers discomforts
    • hazardous driving conditions
    • steps
      • clean
      • ensure vehicle height (suspension, tire pressure)
      • ensure flat parking surface
  • display
    • LCD liquid crystal displays
    • LED light emitting diode
    • vacuum fluorescent display
  • use rosin core solder, butt connect
  • shorting bars are installed in the connectors of an air bag circuit to help prevent accidental deployment

Failure and fluid analysis

  • Fluid analysis info is best utilized under a predictive maintenance program
  • beach marks: fatigue fracture
  • sudden fractures: brittle fracture
  • scraping of cuts and gouges (no heat): abrasive wear
  • material wear/removal due to vibration without lub: false brinelling
  • surface cracks and pitting: surface fatigue wear
  • restricted inlet: erosive wear or cavitation
  • compression stress acts @ 90 to the lines of force and enlarge
  • torsion stress subjects to drive shaft
  • most failure due to operation conditions
  • low oil sump operating temp indicate water is present
  • high wear of brass bushings results in high ppm of copper and zinc
  • dust and dirt: silicon
  • antifreeze: boron and sodium

Orientation to vehicle inspection

  • 2 majors regulations in AB
    • Commercial Vehicle Maintenance Standards Regulation - Motor Transport Act
    • Commercial Vehicle Inspection Regulation - Highway Traffic Act
  • vehicles owned by farmer are exempt from inspection
  • Inspection Methods and Standards Manual is the guide used in inspection process
  • two categories of inspection technician licenses
    • General Inspection Technician’s License
    • Trailer Inspection Technician’s License

Air condition fundamentals

ac

  • comfortable temp: 70-75F or 21-25C
  • comfortable humidity: 40-45%
  • heat moves from a hotter to colder area
  • heat movement methods: convection, conduction, & radiation
  • heat measurement:
    • intensity: Fahrenheit or Celsiush
    • quantity: BTU or J
      • raise water temp from 63-63F require 1 BTU
      • raise water temp from 17-18C require 4.180kJ
  • latent heat is the heat quantity (BTU) that must be added (absorb @ evap) or removed (give up @ condenser) to make a substance change state, but not temperature
  • temp @ which a substance changes state depends on the pressure surrounding the substance
  • saturated conditions: there is only 1 pure refrigerant (gas or liquid) in the container
    • R-134a: 12psi @ 10F; 1.9psi @ -10F
  • evaporator: liquid evaporates to gas
    • add or absorb heat in the cab
    • superheating
      • deal with vapours
      • all liquid has changed to gas, “continue to absorb heat which means superheating”
      • help to protect compressor from liquid refrigerant
      • evaporator’s outlet will be hotter than the inlet 8-12F
        • how well the expansion device is working
        • how efficient the evaporator is working
  • condenser: gas condenses to liquid
    • remove or give up heat
    • subcooling
      • deal with liquid
      • all gas has changed to liquid, “continue to give up heat which means subscooling”
      • condenser’s outlet will be colder than the inlet 12-21F
  • refrigerant
    • R-134a light blue container contain greenhouse gas
    • R12 has chlorofluorocarbon CFC which destroys ozone layer, eliminate production and import Jan 1, 1996
    • as of jan , 2000 can not charge or top up R12
    • Duracool 12a contains hydrocarbons which is flammable
    • no refrigerant should be vented to atmosphere
  • refrigerant oil
    • provide lub, seal, and cool the compressor parts
    • mixed with refrigerant
    • 3 types:
      • mineral oil based (MO)
      • polyol ester (POE)
      • polyalkylene glycol (PAG)
    • MO can NOT mixed with R-134a or PAG
    • R-134a can mixed with POE & PAG
    • “choose POE for topping up any AC system”
  • four events of an AC system
    • expansion (orifice): high pressurized liquid go over an orifice, becoming low pressurized liquid
    • evaporation (evaporator): low pressure liquid absorbs heat, becoming low pressurized gas
    • compression (compressor): low pressurized gas is compressed and added heat by compressor, becoming high hot pressurized gas
    • condensation (condenser): high hot pressurized gas give up its heat, becoming high hot pressurized liquid
  • components
    • compressor and compressor clutch
      • 2 reed valves: suction side and discharge side
      • clutch coil or electromagnetic coil is stationary
      • clutch coil is energized, magnetic field locks the pulley to the drive plate (clutch plate/hub) to engage the compressor
    • service valves
      1. quick-disconnect type or schrader type
      2. stem type valve
        • CCW: normal operation
        • CW: isolate compressor (do NOT operate compressor)
        • Mid-steated: connect to the gauge and compressor (service)
    • condenser types:
      • tube and fin (strongest)
      • serpentine
      • parallel flow (use when mounting room is limited)
    • receiver/dryer: TXV
      • ensure only liquid go to orifice to maximize ac efficiency
      • mounted after condenser (high side)
      • separated vapor and liquid
      • filter is screens and desiccant (commonly uses molecular sieve)
        • to catch any moisture
      • have sight glass may include moisture indicator
        • by changing color of sight glass
      • have high pressure sw
    • accumulator: CCOT
      • help to prevent liquid enter compressor
      • mounted in the suction hose
      • can evaporate a large amount of liquid because of their location
      • use desiccant to trap moisture
    • thermal eXpansion valve (TXV)
      • a variable orifice sensing evap outlet’s temp to control how much refrigerant go to evaporator which ensures that outlet refrigerant is gas which protect the compressor
        • outlet temp decreases, TXV decreases flow of refrigerant
          • outlet temp decrease, it means that subcooling is happening in the suction hose (outlet of evap), which means we may still have liquid in the suction hose, which is NOT good for reed valves, thus, the variable orifice has to decrease its size, allow less refrigerant enter the evaporator
      • 2 types:
        • blocked-type
        • internally/externally equalized thermostatic
          • has capillary tube and sensing bulb
    • evaporator
      • moisture forms into droplets and drains to the bottom of the evap housing
    • air conditioning hose
      • single braid
      • double braid
      • do NOT use hydraulic hoses for AC because they are too porous allowing refrigerant leak
      • fitting: flare or o-ring types
  • TXV system
    • a thermostatic sw senses evap’s temp and turns compressor ON and OFF, giving the operator ability to control over the cab temperature
  • Fixed orifice tube or CCOT system
    • a clutch cycling sw sensings the pressure of suction side to control the temperature of the evaporator
      • CC cw locates in accumulator
      • pressure is high which means warm temp, the sw closes engage the compressor clutch
      • pressure is low which means cold temp, the sw opens disengage the compressor clutch

HVAC control systems

  • active: driver control
    • engine coolant water valves
      • operator set the amount of hot engine coolant that will pass through the heater core
      • a sized open water valve causes the cab remain very warm even when the AC is running
    • compressor magnetic clutch
      • operator turn AC on
      • voltage to the clutch coil
        • too low: drive plate may slip on pulley
        • too high: overheating
      • black coil 12 V
      • green coil 24V: has double resistance of black coil
  • passive: automatic control
    • thermostatic sw (NC, TXV only; replaced by CCOT cycling sw on CCOT system)
      • adjustable can reach 50F for closing point
      • fixed sw
        • open @ 32F, disengage the compressor
          • when the evaporator core is closed to freeze temp, stop the compressor; the heat will warm and defrost any frozen moisture
        • close @ 38F, engage the compressor
          • when the evaporator core is warm, the sw closes the contact, engaging the compressor
    • low pressure sw (NO): use as low ambient temp proection sw
      • 24psi open & disengage the clutch
      • 34psi close & engage the clutch
      • placed in
        • accumulator, protect compressor from low refrigerant pressures due to blocked expansion valve or lack of refrigerant, which results in lack of lub
        • receiver/dryer, sense low pressure from high side and ambient temp is too cod
    • clutch cycling sw (NO, a low pressure sw replace thermostatic sw on CCOT)
      • protect compressor from operating with low refrigerant pressure & no oil circulation
      • located on accumulator
        • open @ 24psi (34F), disengage compressor, defrost evap
        • close @ 48psi (39F), engage compressor, cool evap
      • can have diff range [12, 38] or [24psi, 48psi]
    • high pressure cut-out sw, (NC)
      • open @ 350psi, stop compressor
      • close @ 250psi, start compressor
      • sense high side
      • must lower than pressure relief valve (fusible plug)
      • can use to control condenser fan & radiator shutter systems
        • condenser fan kick in when condenser does not receive enough cooling ram airflow to keep the pressure with normal limits
    • binary sw (low/high pressure sw)
      • provide slow and high pressure protection
      • located bw condenser and expansion device (on dryer)
    • trinary sw
      • located bw condenser and expansion device (on dryer)
      • low pressure sensor (NO):
        • open @ 15-28psi
        • close @ 40psi
      • high pressure sensor (NC)
        • open @ 270-330psi
        • close @ 80-125psi
      • mid range: (NO) controls condenser fan
        • open @ 35-60psi
        • close @ 200-230psi
    • electric refrigerant solenoid valve
      • direct refrigerant to second evaporator’s expansion device
      • open when sleeper compartment call for cooling and cab has to be in operation
    • blower motor and fans
      • “single or double shaft” motor
      • “single or double entry” blower wheels
  • combination and supplemental control devices: may prevent or support system functions. e.i. ambient temp sw, radiator fan clutches and shutter systems
  • AC management system
    • control module
    • monitor (input): high / low pressure, & thermostatic sw
    • control (output)
      • condenser fan (how long is engaged depending on vehicle speed and pressure)
      • compressor clutch
  • automatic temperature control
    • monitor (input)
      • cab temp sensor
      • fresh air temp sensor
      • evaporator temp sensor
    • control (output)
      • heater water valve
      • blower fan speed
      • compressor clutch |— | IC system | manual climate control system |— | water valve controls coolant | coolant is not control | all air flows through evap and heater core | have air door direct how much air to heater core | outlet temp depends on the amount of coolant passing the heater core | depends on air flow through heater core |—
  • sleeper heating
    • heating:
      • extra heater core is hooked in parallel with that of cab
      • electronically controlled water valve installed on return side of coolant on sleeper side, parallel with heater system circuit
    • cooling
      • extra evaporator core and TXV are hooked in parallel with those of cab
      • electric refrigerant solenoid valve installed after dryer on sleeper side
    • fuel-fired air heater (draw 2A/hour) use to reduce premature engine wear on parking truck for sleeping
      • use to heat sleeper compartment
    • fuel-fired coolant heater
      • help engine start up
      • warm sleeper compartment
      • some sense battery voltage and not operate if less than 10.5V
    • aux power units
      • warm by heat from aux engine
      • cool by aux driven air ac compressor
  • use fuse protected jumper wire override the low pressure sw, if clutch engages
    • low refrigerant
    • faulty low pressure sw
    • the refrigerant is too cold to create enough pressure to closed the sw

AC testing and service

  • air should contains 9% of oxygen
  • never fill a refrigerant container over 80% full of liquid refrigerant
  • moisture + refrigerant = acid; moisture can free TXV orifice
  • compressed air + R-134a = combustible mixture
  • refrigerant identifiers
    • identify and measure the purity of refrigerant
  • refrigerant recovery unit
    • the refrigerant is removed in the form of a vapor
    • overfill protection float shuts off the recovery unit when reaching 80% of its cap
  • leak detectors
    • electronic refrigerant leak detectors
      • move the probe to detect
    • flourescent dye leak detection
      • use syringe to inject dye to the system
      • do NOT use red dye, clog station filters, air valves, etc.
    • pressurize ac system with nitrogen 150psi
      • if pressure drop 1psi over 5 minutes, ac system has leaks
  • manifold gauge set
    • access ac system
    • remove air and moisture
    • recover or add refrigerant
    • do visual and perf inspection before hooking up gauge set
    • do NOT hook up gauge set with engine is running
    • do NOT open hand valves, or it create short from inlet to outlet, cause compressor slugging and broken reed valves
  • refrigerant scales: zero scale with empty container, recovery refrigerant, weight it, identify it, and charge
  • high capacity vacuum pump
    • use to remove air and moisture from AC system
    • a vacuum of 500 microns is drawn and held for 20 minutes to ensure that all moisture and air are removed
  • micron gauge, hose crimping, belt tension gauge
  • fin combs are used to straighen the bent fins, clean.
  • schrader valve core service tools
    • use to install or remove schrader valve stems
  • spring lock coupling tools
  • heating system service tools
    • pressure tester
    • apply pressure with air pump, check pressure drop for leak -diagnosis
    • visual inspection
      • use refrigerant identifier to check type of refrigerant
      • check tension should be not over 110lbs
      • bend or kinked condenser tubes causes lower than normal system pressure
      • poor heat exchange in condenser causes higher than normal system pressure
        • bent fins will limit amount of air flow thought the condenser
        • dirt, lint blocks air flow
        • high pressure washing system can bend fins
      • look up for frost build up on any ac components
    • operation tests
      • connect manifold gauge
      • stablized system 15min running time
      • temperature depends on ambient temp, humidity levels, and condenser size
      • low/low/warm discharge air
        • undercharge
        • internal blockage results in cold spots
          • bent or kinked tubes
          • TXV stuck in close position
          • compressor outlet blockage results in clutch slippage, overheating
        • restricted evaporator air flow
      • high/low
        • faulty air compressor
          • broken reed valves, loss of piston ring seal
          • slugging compressor: compressor being filled with liquid
            • overcharge
            • cold weather causes ac system has very little vapor (low pressure sw can be broken)
      • high/high
        • overcharged
        • mixed refrigerant, including air
        • restricted condenser air flow
        • txv stuck in open position or the sensing bulb is broken