Differentials v 2

Differentials and Drive AxlesCHAPTER 7

Purposes of a Drive Axle AssemblyTo transmit power from the engine to the wheelsTo turn the power flow 90 degrees on RWD carsTo allow the wheels to turn at different speeds while corneringAllow for final gear reduction

RWD Axle ComponentsRear axle housing (single)Holds all other components and attaches to the vehicles suspension

RWD Axle ComponentsRing and pinion gearsProvide a final gear reductionTransfer power 90 degrees to the wheels

RWD Axle ComponentsRing and pinion gears

Hypoid GearsThe centerline of the drive pinion gear intersects the ring gear at a point lower than the centerlineThey are commonly used in cars and light-duty trucksTheir design allows for a lower vehicle height and more passenger room inside the vehicleHyperlink

Spiral Bevel GearsThe centerline of the drive pinion intersects the centerline of the ring gearThey are usually used in heavy-duty truck applicationsThey are usually noisier than hypoid gears

RWD Live Axle Components (contd)Differential assemblyContains the differential case which attaches to the ring gearIncludes the side gears and differential pinion gears that allow wheels to turn at different speeds

RWD Live Axle Components (contd)The differential pinion and side gears will always have a thrust washer between themselves and the differential (carrier).

RWD Live Axle Components (contd)AxlesTransmit power from the differential to the wheelsExternally splined at the end to mate with side gears internal splines

RWD Live Axle Components (contd)Bearingspinion (tapered roller)axle (roller)carrier (tapered roller)

FWD AxlesFront wheel drive cars have the engines mounted transversely, thus the powerflow axis is naturally parallel to the drive axles.Because of this, a simple set of helical gears in the transaxle can serve as the final drive gears (east/west placement).

RWD Basic Differential OperationOften referred to as an open differentialThe pinion gear (small) drives the ring gear (large) which is attached to the carrier housing

RWD Open Differential OperationWhen going straight ahead:The differential housing and its components rotate as a single unitEach side gear rotates at the same speedPower is transferred equally to both wheels

Differential OperationWhen turning a corner:The wheels must travel at different speeds to prevent tire scrubbing

Differential OperationWhen turning a corner:Differential pinion gears walk around slower side gear and cause other side gear to turn fasterAn equal percentage of speed is removed from one axle and given to the otherThe amount of torque applied to each wheel remains equal

Differential OperationIf one of the driving wheels has no traction the torque required to turn that wheel is very low.This causes the pinions to walk around the side gear of the axle (wheel) with good traction causing no vehicle movement.The spinning wheel is actually turning at twice the speed read on the speedometer.

Types of Axle HousingsLive A one piece housing with tubes extending from each end.

Types of Axle HousingsIRS (Independent Rear Suspension) The center houses the final drive and differential gearsThe axles are external from the housing.

Rear Axle Housings Integral carrier typeThe differential assembly is mounted in and supported by the axle housingIt is sometimes called a Salisbury-type

Types of Axle HousingsRemovable carrier typeThe differential assembly can be removed from the axle housing as a unitIt is sometimes called a pumpkin-type

Gear Ratios The overall gear ratio is equal to the ratio of the ring and pinion gears multiplied by the ratio of the gear the transmission is inNumerically low gears are said to be highNumerically high gears are said to be lowGear ratios are usually selected to provide the best combination of performance and economy

Calculating Overall Gear RatiosIf the transmission gear ratio is:1.5:1And the final drive gear ratio is:3:1The total final drive ratio is: 4.5:1

1.5 x 3 = 4.5

3 Ways to Determine Final Drive RatioUsing the vehicle service manual, decipher the code on the tag attached to or stamped on the axle housingCompare the number of revolutions of the drive wheels with those of the drive shaftCount the number of teeth on the drive pinion gear and the ring gear

Gearset ClassificationsNonhunting gearsetEach tooth of the pinion gear will come in contact with the same teeth on the ring gear each revolutionThe gearset must be assembled with its index marks alignedAn example ratio is 3.0:1

Gearset Classifications (contd)Partial nonhunting gearsetAny one tooth of the pinion gear will come in contact with some of the teeth on the ring gear each revolutionThe gearset must be assembled with its index marks alignedAn example ratio is 3.5:1

Gearset Classifications (contd)Hunting gearsetAny given tooth on the pinion gear contacts all of the teeth on the ring gear before it meets the same tooth againThe gearset does not have to be indexedAn example ratio is 3.73:1

Transaxle Final Drive FeaturesThe differential operates basically the same as in a RWD axleThere is no 90-degree change in directionThe drive pinion is connected to the transmission output shaftThe ring gear is attached to the differential case

Final Drive Assembly TypesHelicalRequires the centerline of the pinion gear to be aligned with the centerline of the ring gearPlanetaryAllows for a very compact transaxle designHypoidIs quieter and stronger than other designs

Open DifferentialWhen going straight ahead:The differential housing and its components rotate as a single unitEach side gear rotates at the same speedPower is transferred equally to both wheels

Open DifferentialWhen turning a corner:The wheels must travel at different speeds to prevent tire scrubbingDifferential pinion gears walk around slower side gear and cause other side gear to turn fasterAn equal percentage of speed is removed from one axle and given to the otherThe amount of torque applied to each wheel remains equalOpen differential

Limited-Slip DifferentialsProvide more driving force to the wheel with traction when one wheel begins to slipStill allow the wheels to rotate at different speeds when turning a cornerAre sometimes called Posi-Traction, Traction-Lok, and Posi-Units

Limited-Slip Differential DesignsClutch pack typeIt uses two sets of clutches, each consisting of steel plates and friction platesThe steel plates are splined to the differential case and the friction plates are splined to the side gearsDuring cornering, the plates slip, allowing the wheels to turn at different speeds

Limited-Slip Differential Designs (contd)Cone-typeIt uses two cone clutches with one cone that has frictional material on its outer surface and the other with a grooved surface on the insideCones allow wheels to turn at different speeds during cornering, while providing torque to both wheels during straight-ahead driving

Limited-Slip DifferentialDesigns (contd)Viscous clutch-typeIt uses steel and frictional clutch plates that rely on the resistance of high- viscosity silicone fluid for applicationA difference in rotational speed causes the fluid to shear and allows one wheel to turn at a different speed than the other one

Limited-Slip DifferentialGerodisc-typeIt uses a clutch pack and a hydraulic pumpThe pump is driven by the left axle shaftThe pumps output determines how much pressure is applied to the clutch packThe amount of tire slip determines the pressure delivered by the pumpGerotor pumpEaton Gerodisc

Limited-Slip Differential - Torsen

Torsen differential (torque sensing) Designed by Vernon GleasmanGM Audi LexusPeugeotToyotaVolkswagen

Limited-Slip Differential - Torsen

When the torque bias ratio (TBR) is less than than 3:1 one wheel can receive up to 75% torqueThe other will get 25% When the TBR is GREATER than 3:1 the worm wheels tighten on the worm gear and the slower side receives torque from the faster sidevideo

Locked DifferentialsVery limited differential action, if anyMostly off-road or race applications

E-Locker Collar Type

E-Locker Kit

Detroit Locker

Detroit Locker

Spool DesignNo differential operation

Designs of AxleBearing SupportFull-floating axleThe bearings are located outside the axle housingThey are usually found on heavy-duty applicationsThree-quarter and semi-floating axlesThe bearings are located inside the housingThis design is found on passenger cars and light trucks

Types of Axle BearingsBallIs designed to absorb radial and axial end thrust loadsStraight-RollerOnly absorbs radial loads; the axle housing bears the end thrustTapered-RollerAxle end thrust can be adjusted

Independent Rear Suspension Design FeaturesThe differential is bolted to the chassisThe axles are similar to FWD drive axlesEach axle has an inner and an outer constant velocity joint

Differential LubricationHypoid gear types usually use 75W to 90W gear lubeLimited-slip differentials use special fluid or additive toModify clutch plate frictionEase apply/release of clutchesSome applications require ATFSome transaxles use a different lubricant for the transmission and the differential

Noise DefinitionsChuckleA rattling noise that sounds like a stick in the spokes of a bicycle wheelIt is normally heard during coastingIts frequency will change with vehicle speedIt is usually caused by damaged gear teeth

Noise Definitions (contd)KnockingSounds similar to chuckle, but is usually louderCan occur in all driving phasesIs usually caused by gear tooth damage on the drive side or loose ring gear bolts

Noise Definitions (contd)ClunkA metallic noise often heard when an automatic transmission is shifted into drive or reverseMay be heard when the throttle is applied or releasedIs usually caused by excessive backlash somewhere in the drive line or universal joint play/damage

Noise Definitions (contd)Gear NoiseThe howling or whining of a ring gear and pinionCan occur under various conditions and speedsIs usually caused by an improperly set gear pattern, gear damage, or improper bearing preload

Noise Definitions (contd)Bearing rumbleSounds like marbles rolling around in a containerIs usually caused by a faulty wheel bearingBearing whineA high-pitched, whistling noiseIs usually caused by faulty pinion bearings

Noise Definitions (contd)ChatterCan be felt as well as heardIs usually caused by excessive bearing preloadOn limited-slip differentials, it can be caused by using the wrong type of lubricant

Some Causes of VibrationsOut-of-round or imbalanced tires Improper drive line anglesDamaged pinion flangeFaulty universal jointBent drive pinion shaft

Common Sources ofAxle Assembly LeaksDamaged pinion sealLeakage past the threads of the pinion nutLeakage past the carrier assembly stud nutsLeaking gasketsHousing porosityDefective ABS sensor O-ring

Diagnosing Limited-Slip Concerns1. Locate the specification for break-away torque2.With one wheel on the floor and the other one raised, use a torque wrench to check the torque required to turn the wheel3. If the torque is less than specified, the differential must be checked

Fluid Level CheckMake sure the proper fluid is being usedThe vehicle must be levelThe axle assembly must be at normal operating temperatureThe fluid level should be even with the bottom of the fill plug opening

Measuring Ring Gear Runout1. Mount a dial indicator on the carrier assembly2.With the stem of the dial indicator on the ring gear, note the highest and lowest readings3.The difference between the two readings is the ring gear runout

Carrier Removal and Disassembly TipsAlways follow shop manual proceduresMark the alignment of the drive shaft to the pinion flange before disassemblyCheck the ring and pinion side play before removingKeep the shims and bearings in order for reference

Keep the bearings and shims in order for reassembly

Parts InspectionClean all parts before inspectionCheck the bearings for damage or defectsCheck the gears and gear teeth for cracks, scoring, chips, or damage

Reassembly TipsAlways clean the mounting and sealing surfaces before assemblyAlways replace ring and pinion gears in setsUse pilot studs to align the ring gear to the caseCheck the gears for timing marks and properly align if necessary (non-hunting)

Replacing a Pinion Seal1. Check bearing preload before disassembly-Remove the pinion flange2. Remove the seal using a slide hammer3. Lubricate the new seal before installation4. Use a seal driver to install the new seal5. Follow the manufacturers recommendation for tightening the pinion flange nut

Methods Used to Set Pinion Bearing PreloadCollapsible spacer methodThe pinion nut is tightened until the spacer collapses and applies a specific preload to the bearingsNon-collapsible spacer methodUses selective shims to set the proper preload

Checking Pinion Gear DepthCheck the pinion gear for depth adjustment markingsUse special depth-measuring toolsFollow service manual instructions

Differential Case AdjustmentsThe differential case can be adjusted side to side to provide proper backlash and side bearing preloadSome designs use threaded bearing adjustersSome designs use selective shims and spacers for adjustments

Pinion Bearing PreloadCheck the pinion bearing preload using an inch-pound torque wrenchTightening the pinion nut crushes the collapsible spacer to set the preloadTighten the nut in small increments, checking preload after each phaseTake care not to overtighten the nut

Checking Ring and Pinion BacklashMount the dial indicator base firmly on the axle housingPlace the dial indicator against the face of a ring gear toothMove the ring gear back and forth and read needle movementTake readings at several points around the gear

Gear Tooth Pattern

Gear Tooth Pattern

Gear Tooth PatternDriveThe convex side of the toothCoastThe concave side of the toothHeelThe outside diameter of the ring gearToeThe inside diameter of the ring gearHighThe area near the top of the toothLowThe area near the bottom of the tooth

Gear Tooth Pattern

FWD Final Drive ServicePinion shaft adjustments are not necessaryRing gear and side bearing adjustments are necessaryAdjustments are normally made with the differential case assembled and out of the transaxleAlways follow service manual procedures

Clutch Type Limited-Slip Differential ServiceInspect the clutch plates and side gear retainers for wear and cracksRefer to the shop manual to determine the proper way to measure thicknessAfter assembly, check the total width of the clutch pack to determine shim thickness

Tips for Removing Axle BearingsNever use a torch to remove a retaining ringUse a drill or cold chisel to loosen a press fit ringUse a puller to remove a bearing from an axle housingUse a press to remove a tapered bearing from an axle shaft

SummaryThe axle assembly includes the axle housing, ring and pinion gears, differential assembly, and the axlesThe two major designs of axle assemblies are the integral and the removable carrier typesA differential allows one wheel to rotate faster than the other in a turnA limited-slip differential allows torque to be applied to the wheel with the most traction while still allowing the wheels to turn at different speeds while corneringDifferential measurements include pinion depth, pinion bearing preload, backlash, ring gear run-out, and side bearing preload

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