Analisis de Fallas Ejes Meritor

8/18/2019 Analisis de Fallas Ejes Meritor

1/91

Failure Analysis forDrive Axle Components

Manual TP-9955

Issued 06-00


2/91

Service Notes

1

Service NotesThis publication provides failure analysisinformation for Meritor drive axle components.The information contained in this publication wascurrent at the time of printing and is subject torevision without notice or liability.

1. Understand all procedures and instructions.

2. Follow your company’s maintenance andservice, installation, and diagnosticsguidelines.

3. Use special tools when instructed to avoidserious personal injury and damage tocomponents.

Access Information on Meritor’sWeb Site

Visit the Technical Library section of Meritor’s website at www.meritorauto.com to access the items

listed below, as well as additional product andservice information on Meritor’s heavy vehiclesystems component lineup.

Product and Service Information

To order the items listed below, call Meritor’sCustomer Service Center at 800-535-5560.

r

Single Reduction Differential Carriers

maintenance manual. Order MM-5.

r

Single Reduction Rear Differential Carriers

maintenance manual. Order MM-5A.

r

Tandem Axle Forward Carriers and Single AxleCarrier

maintenance manual. Order MM-5E.

r

Tandem Axle Single Reduction ForwardDifferential Carriers

maintenance manual.Order MM-5L.

r

Technical Electronic Library

on CD. Featuresproduct and service information on mostMeritor, ZF Meritor and Meritor WABCOcomponents. $20. Order TP-9853.

Safety Alerts, Torque Symboland “NOTE”

WARNING

A WARNING

alerts you to a procedure thatyou must follow exactly to avoid seriouspersonal injury and damage to components.

CAUTION

A CAUTION

alerts you to a procedure thatyou must follow exactly to avoid damage toequipment or components. Serious personalinjury can also occur.

TORQUE

The TORQUE

symbol indicates that you musttighten fasteners to a specific torque value.

NOTE:

A NOTE

can either indicate a procedure orinstruction that is important for correct service,or provide service suggestions.


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Table of Contents

Section 1: Overview of Component DamageOverview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Shock Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Fatigue Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Typical Fatigue

Identification

Surface Fatigue — Pitting, Spalling and Flank Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Surface or Contact Fatigue

Pitting Fatigue

Spalling Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

Spalled Gear Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Flank Cracking

Rotating Bending Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Torsional Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Bending — Root Beam Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Bending — Deep Root Tooth Fatigue

Typical Spinout Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Other Indications of Spinout Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Lubrication-Related Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Contamination Damage

Types of Lubrication-Related Damage

Depleted Additive Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

Incorrect Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Overheated Operation Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Low Lubricant Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Lack of Lubrication

Fretting and Brinelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Indications to Look Further — Secondary Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

Section 2: Causes of Drive Axle Damage

Drive Axle Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

Vehicle Application/Vocation

Axle Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

Housing Overload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

Vehicle Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Operational Component Damage

Cause of Spinout Damage

Potential Differential Spinout Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

Typical Shock Load Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36

DCDL Lock Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38

Maintenance and Rebuilding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

Maintenance and Rebuilding Practices

Lubrication-Related Component Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

Tire Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Torsional Vibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Vehicle or Powertrain Modifications


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Table of Contents

Section 3: Damaged Axle Review

Tapered Roller Bearing Damage Analysis — Printed Courtesy of Timken

Identifying Axle Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Bearing Adjusting Ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Drive Pinion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Drive Pinion Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Drive Pinion Root Beam Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Driveline/Torsional Vibration Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Driver-Controlled Differential Lock (DCDL) Collar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Flange Side Differential Bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Housings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Hypoid Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Hypoid Set (Both Ring and Drive Pinion Gears) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Hypoid Gear Set (Inner Drive Pinion Bearing) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Inner Pinion Bearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

IAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

IAD Spider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Low Lube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65Main Differential Spider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Main Flange Side Differential Bearings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Pinion Nut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Plain Half Differential Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Main Differential Case-to-Case Joint Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Pump Systems — Screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Rear Side Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Ring Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Side Gear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Side Gear Thrust Washer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Thrust Washers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82


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Section 1Overview of Component Damage

1

Section 1Overview of Component DamageOverview

The following section provides basic informationand definitions used in the field evaluation ofdamaged components. When possible,

photographs of components are presented toillustrate the types of severe damage commonlyfound during component teardowns. Techniciansand drivers are sometimes surprised to findseverely damaged components that havecontinued to function for a long time. The signs ofthese types of extreme damage are not alwaysreadily apparent to the vehicle driver. Much of thesevere damage to the parts presents a learningexperience to everyone involved in the heavytruck industry.

Damage analysis can be viewed as a specializedand highly technical activity. At various times, it

involves engineering, component design,metallurgy and chemistry.

From the perspective of fleet management, effortsput into an analysis of damaged axle assemblycan mean a future reduction in the cost of vehicleservice repair and can promote optimum vehicleperformance between regularly scheduledmaintenance intervals.

Component damage often means expensive repairwork, equipment downtime and inconvenience.This is the reason that it is important to recognizethe cause. If components are simply replacedwithout correcting the cause, further trouble may

be encountered not only in one vehicle but withthe other vehicles in a fleet.

The challenge of achieving maximum productservice life is a responsibility shared by thetechnician and the vehicle operator. A vehicle is atool designed to work under a specific conditions.Knowing how the equipment operates, the limitsof its operation and how the components can bestressed to the point of failure is necessary inorder to avoid downtime and costly rebuildoperations.


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2

Shock Damage

When a component (gear tooth or shaft)experiences a sudden and powerful force thatexceeds the strength of the component, it breaks.

A shock load can fracture components instantly,crack them or cause them to fatigue and fail at alater time.

When the shock load overstresses the componentmaterial and is delivered in one high impact load,an instantaneous break will occur.

Failure caused by a shock load is most easilyidentified by the rough, crystalline finish that isusually found where the parts separate from eachother at the time of instantaneous overload.Figure 1.1

.

Shafts loaded under torsion can fracture

perpendicular to the axis. Figure 1.1

.The fracture can also be at approximately a45° angle to the axis if the axle shaft is allowed towind-up. Figure 1.2

.

Figure 1.1

39218d16

Rough crystalline surface

Figure 1.2

39213d6

45° fracture


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3

The overhanging pinion in Figure 1.3

wasdamaged due to a rotating shock load. Thefracture has a rough, crystalline appearance and isbroken at a 45° angle.

The ring gear in Figure 1.4

was broken in aninstantaneous shock load. A typical instantaneousfracture of the ring gear will have three adjacentteeth broken at the root of each tooth. The fracturewill have a rough, crystalline appearance.Typically with a hypoid gear set, the first tooth willbreak at the heel, the majority of the second toothwill break, and the third tooth will break at the toe.In Figure 1.4

two of the fractured teeth have beenmarred from the pinion rubbing against the areaafter the teeth broke off.

NOTE: See appropriate axle maintenance manualfor gear teeth nomenclature.

Shock Initiated Fatigue (SlowRepeat Overload)

Shock loads are often severe enough to break offgear teeth at their roots, break drive-axle shaftsinto two pieces, as well as cause other damage.Sometimes a shock load does not cause thecomponent to fail instantaneously but cracks orweakens it. Depending on the severity, the finalfailure may not occur until many miles later.

Figure 1.5

.

Figure 1.3

JIM use 21

Figure 1.4

JIM USE 12 OR 13

1 Rough crystalline area2 Smeared

Figure 1.5

39218d13


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4

Fatigue Damage

A typical fatigue fracture (

Figure 1.6

) is caused byrepeated overloading of a component. The fatiguefracture will typically show arrest lines (beach

marks), as the fracture progresses during repeatedoverloading. Fatigue fractures begin at one ormore initiation points, and are identified by thelocation of an eye and/or one or more ratchetmarks, from which all the beach marks radiate.

Typical Fatigue

When the bending or torsional load is large, thepart will fail after a small number of loadapplications. As the load is reduced, it requires agreater number of applications to cause failure.

When the load is decreased even further, the part

can withstand an infinite number of applicationswithout failing. The load corresponding to thehorizontal part of the diagram is called the“endurance limit” of the material.

Plotting both lines on the same graph shows therelationship between the fatigue due to surfaceloads and that due to bending and/or torsionalloads. Figure 1.7

.

Identification

Four types of fatigue failures are common indrive-axle carriers. Each is identified by different

characteristics:

r

Surface or contact fatigue

r

Rotating bending fatigue

r

Torsional fatigue

r

Root beam fatigue

Surface or contact fatigue affects contact surfacesof the gearing and bearings. Rotating bendingfatigue affects shafts. Torsional or contact fatigueaffects shafts. Root beam fatigue affects gearteeth.

Figure 1.6

39218d35

1 Point of origin2 Beach marks (“witness”)3 Final fracture

Figure 1.7

chart 1

SURFACE AND BENDING/TORSIONAL FATIGUE

MANY

BENDING

OR

TORSIONAL

FEW

SMALL

LARGE

SURFACE

LOAD

NUMBER OF APPLICATIONS


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5

Surface Fatigue — Pitting,Spalling and Flank Cracking

Surface or Contact Fatigue

Surface fatigue is a broad classification for anumber of different damage modes that occur onthe load-carrying surface of a component. It isusually caused by cyclic overloading of thecontacting surface of a bearing or gear tooth andcan be accelerated by debris in the lubricant.

Surface or contact fatigue affects the contactsurfaces of bearings and gears. It is the mostcommon form of fatigue and is characterized byvarying degrees of pitting, and sometimesspalling, of gear tooth or bearing surfaces.

Figure 1.8

. Unlike wear related to inadequate

lubrication due to water contamination orsuspended debris, surface fatigue can also resultfrom repeated overstressing of a component andcan take place even when proper lubrication isprovided to the working parts.

Pitting Fatigue

Pitting is a type of metal fatigue in which smallcavities form on the surface of the metal. Initially,pits may be the size of a pinhead or smaller. Ifunchecked, pitting will progress and eventuallypieces of the surface metal will begin to breakaway.

Usually, at this point component operationbecomes irregular, rough and noisy.

Consequently, destructive pitting moves past thesurface and deeper into the metal. Metal particlesbreak away from the bearing surfaces and canthen recycle in the axle lubrication system. Thispromotes further contact surface deterioration,typically in the bearing cups and rollers. It will alsoaccelerate fatigue and promote premature wear ofthe sliding and rolling contact surfaces of the axlehypoid gearing.

This stage of surface pitting can contribute to axle

noise. In any case, when left unchecked, theprocess of destructive pitting ultimately leads tofull bearing failure.

Surface fatigue pitting damage to the bearingrollers is a sign of contaminated lubrication and/orvehicle overloading. Figure 1.9

.

Figure 1.8

39251d23

Figure 1.9

39251d28

This illustrates an advanced stage of pittingresulting in spalling.


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6

Spalling Fatigue

Sometimes a series of small pits is joined by alifting away of the smooth surface metal betweenthem, and eventually larger metal particles are

“spalled” from the surface. Figure 1.10

. Largerand deeper cavities that evolve from a pittedsurface are known as “spalled cavities.”

Spalling can evolve from pitting when a series ofpitted areas accumulates. Oil enters the pittedcavities close to one another and exerts hydraulicpressure on the surface area between the pittedcavities. The surface area between the pittedcavities is then lifted away, forming a larger,elongated cavity.

Spalling is caused by sub-surface shear and canbe present without pitting.

When spalling occurs on the hardened surfaces ofbearing cups and rollers, the primary cause isusually high contact stress. Unlike the shallowuniform diameters seen in the early stage ofpitting, spalled areas often are not uniform indiameter. Figure 1.11

.

Sometimes severe spalling on bearing rollers issecondary, resulting from a contaminated axlelubrication system. Sometimes pitting precedesthis type of spalling, but contamination is theprimary root cause. Figure 1.11

.

Axle lubricant contaminated with metal particlesor water can accelerate destructive pitting and/or

spalling of the bearing components.Spalling can also occur from a combination ofboth heavy loading and contaminated oil.

Figure 1.10

39278d07

Figure 1.11

39251d28 and 39282d18


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7

Spalled Gear Teeth

Signs of pitting or spalling on gear teeth andbearing surfaces indicate repeated marginaloverload or inadequate lubrication. Marginal

overload is similar to total component failure.Instead, the part is slightly stressed above designlimitations to a point just short of instantaneousdamage over a long period of time.

Contaminated lubricant or lubrication systemproblems that allow excessive metal grindingbetween rolling or sliding surfaces can lead topitting or spalling.

Localized spalling on drive pinion teeth can be asecondary sign that another axle component isrunning out of position. Figure 1.12

.

Flank Cracking

Flank cracking usually causes a metal surface toflake away much like a spalling condition would. Agear with flank cracking, however, will firstdevelop longitudinal cracks that run the length ofthe gear tooth face. Once these cracks appear,failure occurs rapidly. Frequently, a single toothmay show signs of deterioration, while theremaining teeth remain intact. Once the cracksappear, the metal between them begins to flakeaway. Figure 1.13

.

Figure 1.12

39278d4

Drive pinion teeth

Figure 1.13

39367-11

Crack


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8

Rotating Bending Fatigue

This type of fracture occurs when a shaft issubjected to a torsional load and a bending load atthe same time.

Contoured lines, or “beach marks,” on the face ofa broken component represent fatigue “cycles”that occurred before the total breakdown of thepart. These “witness” marks usually point towardthe origin of the fracture. For example, beachmarks originating at an oil passage may spreadacross the surface of a fractured component.Figure 1.14

.

The final fracture will be a rough, crystalline area.This portion broke off instantaneously because thefatigue had weakened the part to the point it couldno longer carry the load. Figure 1.14

.

If the broken pieces continue to turn, the beachmarks and chevrons will be smeared/marred fromthe fracture surface. Figure 1.15

.

Figure 1.14

39218d35

1 Point of origin2 Beach marks (“witness”)3 Final fracture

Figure 1.15

39237d04

Smeared beach marks


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9

Table A: Typical Rotating Bending Fatigue Failures in Shafts

Torsional Fatigue

Torsional fatigue results from excessive twistingforces that weaken a shaft and cause it to fail.Unlike rotating bending fatigue, torsional fatiguehas no bending force introduced with it. When the

failure forms a flat surface, it is common for thebroken ends to rub against each other, smearingthe beach marks on the two surfaces into a swirledpattern. This sometimes makes it difficult todistinguish between fatigue and instantaneousfailure modes.

Repeated overloading caused a torsional fatiguefailure on the axle shaft shown here. The conicalstar-shaped pattern is characteristic of reversetorsional fatigue in the splined area of a shaft.Figure 1.16

.

The conical, star-shaped radial pattern initiallystarts at the root of each spline and finally breaks

off in the center of the shaft.

StressCondition No Stress Concentration Mild Stress Concentration High Stress Concentration

Case

Low

Overload

High

Overload

Low

Overload

High

Overload

Low

Overload

High

Overload

One-way Bending Load

Two-way Bending Load

Reversed Bending andRotation Load

Figure 1.16

39213d13


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10

Bending — Root Beam Fatigue

This mode of fracture occurs when the beam is inan overloaded condition and is flexed back andforth from one position to another. Under normal

loads, this flexing is not a problem, except that astress riser (notches and holes at the radius) canreduce the total strength of the component.

Bending loads can be applied in various waysincluding “cantilever” or “simple.” Figure 1.17

.

Bending — Deep RootTooth Fatigue

This mode of fracture appears in gears and isusually characterized by the same contouredbeach marks that appear in shafts that fracturefrom fatigue loads.

Root bending fatigue generally results from astress crack originating at the root sectionsbetween the gear teeth. A tooth or part of a toothbreaks away, leaving an “eye” or focal pointwhere the beach marks begin. The break showssigns of fretting, and smooth beach marks appearat the beginning of the break area. The small areaopposite the eye is usually rough and jagged inappearance, indicating that this was the lastportion of the tooth to break away.

Root bending fatigue results from shock and/orrepeated overloading, which causes localizedfatigue cracks in the gear roots. As mileage

accumulates, the initial cracks grow larger and thegear teeth progressively weaken and ultimatelybreak.

In drive pinion gears, root bending fatigue ischaracterized by the same contoured beach marksthat appear on shafts that failed due to rotatingbending fatigue. If only two or three teeth havebroken out but no other teeth are cracked, aninstantaneous shock overload can be suspected.Shock induced fatigue will also exhibit origins thatare in line. If all the remaining teeth are cracked, asevere application with continuous moderateoverstress or vehicle overload was the probable

cause.Typical root bending fatigue beach markings startat the roots of all affected teeth and progress tothe outside hardened surface of the hypoid gearset. Figure 1.18

.

Figure 1.17

Cantilever and Simple

Figure 1.18

PC PHOTO 39217-13

1 Ratchet marks2 Beach marks3 Marred area4 Final fracture

LOAD

LOAD


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11

Typical Spinout Damage

A spinout typically occurs when a tandem axleloses traction and the Inter-Axle Differential (IAD)is left in the unlocked position. In axles without an

oil pump, the IAD is getting no lubrication whilethe IAD pinions are turning at almost twice thespeed of the driveshaft. Any oil between the IADpinions and spider leg is lost due to centrifugalforce. The heat created from the friction will allowthe pinions and spider to gall or seize.

Figure 1.19

shows the parts of an IAD assembly.Figure 1.20

shows a failed IAD assembly. The casefractured after the spider and pinions seized.

The IAD is integral to the operational dynamics ofthe tandem axles but is more susceptible tospinout damage than the main differentialbecause it operates at higher speeds and is notsubmerged in oil.

Figure 1.19

Roush 31 or 32 Explode w/out bolts

Figure 1.20

39192d12


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12

The following illustrations show progressive wearof the spider, from light to catastrophic:

Figure 1.21

shows normal wear.

The wear in Figure 1.22

is moderate step wear.

Figure 1.21

PC PHOTO 39176-5

Figure 1.22

Roush 13


17/91


13

The heavy wear and galling most likely resulted inmultiple spinout events but not one spinout eventwas long enough in duration to cause a seizure,although several such events can causecatastrophic damage. This damage can also be

caused by mismatched tires or axle ratios. Figure1.23

and Figure 1.24

.

Sometimes it is a combination of mismatchedtires/ratios and multiple spinout events.

Galling is typically known as metal transfer. Thisoccurs when two metal surfaces move against oneanother with no lubricant. Figure 1.25

is anexample of a galled spider due to spinout damage.

Figure 1.23

39192d38

Figure 1.24

39182-22

Figure 1.25

39182-13


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14

The catastrophic damage in Figure 1.26

is anexample of a severe spinout.

The root cause of a broken IAD differential caseassembly must be evaluated. Thrust washer

grooving on the inside of the case is evidence ofrepeated spinout events. Figure 1.27

.

NOTE: The metal particles of the thrust washerembed into the IAD case. This is an indication thethrust washer was installed at the factory.

In an extreme example, the IAD case may separatedue to spinout damage. Figure 1.28

.

NOTE: The stepped wear pattern on the casehalves is caused from the pinions after the casehalves separated.

Figure 1.26

JIM 16, 17, 18 or 19

Figure 1.27

39192d15b

Embedded thrust washer particles

Figure 1.28

PC PHOTO 39217-15

Secondary step wear


19/91


15

If spinout damage is suspected and the IAD casedid not separate, Figure 1.29

, check the following:

1. Excessive looseness of the pinions to thespider.

2. Metal debris from worn spider legs on theinside of the IAD.

3. Roll the pinions to check if they are seized.

4. The pinion may still spin even though it seizedto the spider and twisted the leg from thespider hub. While turning the pinion, check toensure the spider leg is not turning with it.

Figure 1.29

Roush 25 Welded


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16

Another example is galling on spider legs and oneor more of the pinions twisting the leg from thespider hub. The assembly could not continue tofunction. The primary damage is due to a spinout.Figure 1.30

.

Other Indications ofSpinout Damage

Friction from spinout can cause galling at thehelical gear journal and the rear side gear journal.Figure 1.31

. Spinout damage can also show up ona scored rear side gear bearing. Figure 1.32

. Weknow the bearing was not damaged from preloadbecause the input shaft bearing was not damaged.Improper preload of a bearing generally shows upas spalling. The rear side gear can also be frictionwelded to the input shaft. Figure 1.33

.

Figure 1.30

39182-11

Figure 1.31

39367D19

Figure 1.32

PC PHOTO 39182-3


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17

Sometimes spinout damage is caused from a rearwheel spinning and the front axle sittingstationary, not allowing the hypoid gear set tosplash oil on the internal parts. Figure 1.33

.Generally there is evidence of localized heat and

burnt or carbonized oil in the input shaft area. Therear side gear is usually seized to the input shaftjournal, and in addition, the rear side gear bearingwill be scored.

Figure 1.33

PC PHOTO 39233-2


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18

Lubrication-Related Damage

Improper maintenance can lead to damage,resulting from contamination, overheatedoperation and/or depleted additives.

Contamination Damage

If the lubricant becomes contaminated with water,dirt or wear particles, the wear between matingsurfaces can significantly increase. The source ofthe contamination must be determined. This mustinclude inspection of all seals and breathers.

Contaminants are particularly harmful to bearingsurfaces. Figure 1.34

.

Types of Lubrication-Related

Damage

Etching — Corrosion

Etching or corrosion appears as a dull mattesurface stain or blemish that can indicateproblems primarily caused by moisturecontamination of the axle lubricant. Moisture andwater may enter the carrier through breathers or abroken or worn seal or develop from condensationduring humid weather conditions. In any case,water in the lubricant causes specific harm to thebearing races and cups and will affect wear of thehypoid gear set.

Corrosion from water appears on the bearingsurface. In this case the corrosion showed up onthe spigot bearing roller ends. Figure 1.35

.

Figure 1.34

39367d35

Figure 1.35

39176d30


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19

Etching on the bearing rollers, corrosion onnon-contact surfaces and worn cage windowsindicate water contamination of the lubricant.Figure 1.34

and Figure 1.36

.

Figure 1.36

39176d20


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20

Bruising (Particle Denting)

Bruising occurs when metal chips or largeparticles of dirt circulate in the lubricant and endup trapped between the bearing cone and cup

race. The number of indentations and the depth ofthe bruising determines whether the bearingsurfaces were undergoing normal hydraulicfatigue or the surface is experiencing bruising orabrasive wear deterioration. These features aretypically caused by contaminated axle lubricant. Ifhydraulic destructive pitting occurs, the metalparticles that flaked away may cause racebruising.

Figure 1.37

shows that bruising is beginning toappear on the race.

Scuffing

Scuffing is a localized type of surface wear causedby the breakdown of the lubricating oil film. Thispermits a “tearing” of one metal surface and awelding transfer (galling) to another metal surface.The contact area of bearing cone rollers and themating inner race surface is a good example of anarea in which scuffing, scoring, and spalling canappear before primary failure occurs.

Flat spots appearing on rollers are an indication ofbearing scuffing. The scoring condition of theremaining assembly suggests insufficientlubricant as the primary cause. Figure 1.38

.

If a rough, scuffed surface develops in the earlystages of bearing wear, scuffing, scoring andridging (“crow‘s-feet” in gears) can impedebearing roller operation. This will cause flat edgesthat progressively develop into total bearingfailure.

Figure 1.37

Roush 1-4

Figure 1.38

39192d02


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21

“Crow‘s-foot” scoring is inherent in hypoid gearswhen the wrong or depleted lubricant is used. Thehypoid gears used in Meritor axles develop atremendous amount of loading in the gear contactarea. If oil without the proper level of extreme

pressure (EP) additive is used, the force developedduring loaded gear engagement will causemetal-to-metal contact between drive and drivengears. Because of the combination of sliding androlling action seen in hypoid gearing,“crow‘s-footing” will appear on tooth surfaces.Figure 1.39

.

EP additives will begin to break down when theinternal temperature of a carrier is consistentlyabove 250°F (121°C). Higher temperatures willcause the additive to break down even faster. Adepleted EP additive will not adequately protectthe gears from surface fatigue. Figure 1.39

and

Figure 1.40

.

Depleted Additive Damage

Meritor drive axles require an EP (extremepressure) lubricant with sulfur/phosphorusadditive. The gear oil required is a GL-5 type thathas been tested and approved under theMIL-PRF-2105E specification. An improper gradelubricant, a lubricant with depleted additives orsituations of low lubricant (or none at all) cancause the drive pinion and ring gears to take onthe characteristic contact wear pattern known as“crow‘s-feet.” These patterns are described as

scoring lines or ridges on the gear teeth.Figure 1.39

and Figure 1.40

.

Figure 1.39

39282d22

“Crow‘s-foot” pattern

Figure 1.40

39282-20

“Crows‘s-foot” pattern


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22

Incorrect Lubrication

If an oil without an EP additive is used, the teeth ofa hypoid gear set will quickly wear.

The drive pinion teeth are worn to a thin, knife-likeedge due to incorrect or depleted lubricant.Figure 1.41

and Figure 1.42

.

If detected early, there will be light“crow‘s-footing” present. Once the gear set wearsthrough the steel’s case, hardening into the softermaterial, the teeth are worn to a knife-edge orcompletely away. The gear surfaces will usuallynot show excessive heat and burned oil as seen ina lack-of-lubricant failure. Here, the oil will becontaminated with metal debris due to wear.Generally the pinion will be worn more than thering gear because of more contact time per tooth.

Meritor transmissions require a lubricant that iseither a heavy-duty engine oil (straight grade) orpetroleum GL-1 oil with rust and oxidationinhibitor (mineral or synthetic).

Drive axle lubricants (GL-5, GL-4) MUST NOT beused in transmissions, and transmission lubricantsMUST NOT be used in drive axles. Mixing the twolubricants accelerates premature wear anddeterioration of parts in the assembly. For furtherlubrication information, refer to MaintenanceManual 1, Lubrication

.

Figure 1.41

39259d23

Figure 1.42

39192-46


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23

Overheated Operation Damage

Higher than normal operating temperatures arecaused by one or more of the followingsymptoms:

1. Low lubricant level.

2. Overfilling the assembly with lubricant.

3. Increasing the engine horsepower or torquerating.

4. Restricted ventilation air flow.

5. Incorrect lubricant grade or viscosity.

The ring gear has obvious signs of lubricant thatwas operated in an overheated environment. Thelube in this carrier would have a strong, burnedlube odor. Figure 1.43

. The overheating condition

became hot enough to soften the drive pinionteeth and bearing to a plastic-like state.Figure 1.44

.

Figure 1.43

39196d08b

Figure 1.44

39196d08a


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24

Low Lubricant Levels

When lubricant levels are reduced, the life ofbearings, gears and thrust washers are adverselyaffected. Damage due to low lubricant levels is

characterized by a “crow’s-foot” pattern on thegear set teeth, excessive wear, severely distortedpinion head and inner pinion bearing, and astrong odor to the burned oil seen on internalparts. Figure 1.45

and Figure 1.46

.

Because the ring gear is partially submerged inthe axle oil and has less contact wear (about onequarter as much contact wear as the drive piniongear), the drive pinion gear is the one that usuallysuffers from low lubricant levels. Any axleoverheating due to low lube can progress to thepoint that the gear tooth metal of the drive pinionsoftens and deforms. Figure 1.45

.

Lack of Lubrication

If an assembly was not filled with lubricant,damage most likely occurs at relatively low milesafter installation. “Bluing” of internal parts andplastic deformation of loaded gear teeth arecommonly seen with no initial lubricant. Ofcourse, there would be no burned oil becausenone was put in the unit.

Figure 1.45

39196d010

Figure 1.46

39196-11


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25

Fretting and Brinelling

Fretting is a wear process caused by contactvibration between two different metal surfaces. Itis also known as brinelling, friction oxidation,

chafing fatigue and wear oxidation.

Fretting happens when vibration causes the rollersof a stationary bearing to slide up and down onthe race. If vibration continues for a long time,grooves are worn into the race. Vehicles shippedby rail, truck or boat over long distances are moresusceptible to bearing fretting.

In gears, stationary fretting wear appears assludge debris at or near the point of vibration.Sludge debris forms from the vibration contact ofthe two metals combining metal oxides withgrease or lubricant.

The color of the sludge depends on the quality ofthe lubricant and the type of iron oxide that isformed. Sometimes the sludge mix is called “redmud” or “cocoa.” These oxides are generallyabrasive and so increase component wear. Thiswear, however, is not as severe as in the case ofmetal particles produced by pitting.

Fretting is common in cases of torsional vibrationof the driveline, which can be identified by hardlines of contact on the rear side gear teeth.

Figure 1.47

.

Figure 1.47

39251d13

Flat spotting


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26

Indications to Look Further —Secondary Damage

The drive pinion teeth have been broken off at the

head-end due to misalignment. Beach marks arepresent and will indicate the point of origin. Noticethe initial fracture started at the root of theheel-end, unlike a root beam bending fatiguefailure. Figure 1.48

. This is an indication ofconcentrated loading at the heel-end. Figure 1.49

.The pinion is not designed to absorb the loadingon the corner of the tooth. The loading should bespread over the entire surface of the gear teeth.The damage caused here is an indication of apositioning problem of the ring and pinion. Adetermination must be made as to what affectedthe gear tooth positioning.

The ring gear has a dual contact pattern. Theoriginal pattern indicates the ring and pinion wereoriginally set-up correctly. The second patternhappened after the ring or pinion moved out ofposition. A determination needs to be made as towhat affected positioning. Figure 1.50

.

Sometimes the misalignment of a bearing or poorset-up will cause the above damage.

Figure 1.48

39217-12

Figure 1.49

JIM USE 22 OR 23

Teeth broke in fatigue at heal end.

Figure 1.50

39217d01

1 Original pattern2 Secondary pattern


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27

Top lands of the pinion teeth have been smeared.Figure 1.51

. The top lands of the ring gear havebeen smeared and several teeth have been brokenoff at the toe-end. Figure 1.52

. This damage is anindication to look further. The gear teeth broke

from a foreign object going through the gearmesh. The lands were smeared after the ring andpinion ran out of position.

The adjusting ring on the flange side has beenpushed out. The threads on the adjusting ringhave been stripped and the cotter pin bent. Aforeign object went through the gear mesh andthe forces created are naturally transmitted out theflange side. The adjusting ring being made ofpowder metal would be the weakest part andwould break. Figure 1.53

.

A determination as to what foreign object wentthrough the gear mesh and caused the secondary

damage needs to be made.

Figure 1.51

39259-03

Figure 1.52

39259-09

Figure 1.53

39203-06


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28

If a carrier is heavily loaded due to load weight,engine torque or application, the wear on the ringgear teeth can be a visible indication.

A normally loaded gear tooth will still have milling

marks across the face of the tooth and phosphatecoating will still be visible on both the toe and heelends. Figure 1.54

.

A heavily loaded gear tooth will have the millingmarks worn away and the phosphate coating willbe wiped from the face of the gear tooth.

Figure 1.55

.

A determination needs to be made as to theapplication and rating of the carrier.

Figure 1.54

Jk01

Phosphate coating; Milling scratches

Figure 1.55

Jk02

Smooth face


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29

The side gear teeth in Figure 1.56

have been shockloaded. More than one adjacent tooth, where eachpinion would ride, has been broken at the root.The fracture is rough, crystalline in appearance.These are known characteristics of an

instantaneous shock load.

The side gear in Figure 1.57

has also been shockloaded, but notice the teeth have been brokenhalfway up the face near the pitch line. Thefracture has been smeared, but if it were not, itwould have a rough, crystalline appearance. Weknow the gear has been heat treated because ofthe brittle appearance of the break. The untreatedgear, Figure 1.58

, looks rolled over at each endand the teeth are worn to the root. Both ends ofeach tooth remained because there was nosurface contact with the contacting teeth in thisarea. An instantaneous fracture, Figure 1.56

, due

to shock load would remove the teeth at theirroots. The gear teeth in Figure 1.57

were brokennear the pitch line. They broke in this locationbecause of a concentrated load induced on aportion of the gear teeth face instead of on theentire surface. This type of loading was induceddue to the gear being out of position. Thissecondary damage would be an indication toinvestigate further.

Figure 1.56

Out of position gear

Figure 1.57

Shock loaded gear

1. Brittle appearance2. Broken at pitch line, not root

Figure 1.58

Soft gear

1. Teeth worn to root2. Part of the gear tooth left at each end3. Ends rolled over


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Section 2Causes of Drive Axle Damage

30

Section 2Causes of Drive Axle DamageDrive Axle Damage

The basic reasons for damage of drive axles fallsinto general categories:

1. Vehicle application or vocation2. Vehicle operation

3. Maintenance

4. Vehicle or powertrain modification

Vehicle Application/Vocation

Preventing damage starts with understanding theapplication or vocation intended for the vehicle.All vehicles and their components are designed togive satisfactory service under given operatingconditions. Axles in particular are available in awide range of capacities to meet the requirementsof a wide variety of applications. Axles used inoperations which exceed their design limitationswill result in premature damage and reduced axleservice life.

a. Drive axles are rated in terms of themaximum weight capacity of the housingon the road — in other words, the weight onits back. This is called the “Gross AxleWeight Rating” (GAWR).

b. The axle gearing is rated in terms of totalvehicle weight. The total vehicle weight isGVW (Gross Vehicle Weight) for straight

trucks, buses, etc., and GCW (GrossCombined Weight) for combinationvehicles. Figure 2.1

. The rating (GVW orGCW) determines the amount of work thedrive axle gearing must do to move thevehicle.

c. Road grades also affect the axle gear rating.

d. The type of road surface determines theroad rolling resistance. The harder andsmoother the surface, the lower theresistance. The softer and rougher thesurface, the greater the effort required.

It is essential that the vehicle be properly specifiedto match the job it has to perform. The powertrainmust provide adequate power and gear ratio stepsto ease the vehicle into motion as well as to moveat operational speed. Care in specifying the axle tomatch vocational needs is the first and mostimportant step toward ensuring satisfactoryperformance and service life.

NOTE: For additional information on Meritor AxleApplication Guidelines, contact Meritor‘sCustomer Service Center at 800-535-5560.

Figure 2.1

GVW

GCW


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31

Axle Fatigue

Fatigue is a common type of component damagein an axle assembly. It results from repeated cyclicloading of a component. A single load cycle may

not be great enough to cause the part to breakdown, but repeated load cycles will graduallyweaken the part to the point of failure.

Three types of fatigue components are common inaxle carrier:

r

Surface or contact fatigue, which affectsbearings and gear teeth

r

Torsional fatigue, which affects shafts

r

Bending fatigue, which affects gear teeth andshafts

Steel parts subjected to different types of fatigue

load will show different characteristics. That is, thecharacteristics of damage resulting from surfaceor contact fatigue loaded parts (such as bearingsand gear teeth) differ considerably from thoseresulting from bending or torsional fatigue (as inaxle shafts).

Figure 2.2

shows the characteristics of partssubjected to surface or contact fatigue. When thesurface or contact load is large, component failureoccurs within only a few cycles, as indicated bythe breakdown line. As the load becomes smaller,the number of cycles required to destroy the partincreases. No matter how small the load, repeatedcycles will eventually result in failure from surfacefatigue. The fatigue characteristics of bearings,which are subjected to surface loads, follow thesurface fatigue breakdown line.

Figure 2.2

SURFACE FATIGUE

MANYFEW

SMALL

LARGE

BREAKDOWN LINE

LOAD

NUMBER OF CYCLES


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32

Figure 2.3

represents the characteristics of partssubjected to bending or torsional fatigue. Whenthe load is large, component failure occurs withina small number of cycles. As the load becomessmaller, the number of cycles required to damage

the part increases. When the load decreases evenfurther, the part can withstand an infinite numberof cycles without damage. The load correspondingto the horizontal part of the diagram is the“endurance limit” of the material. Shafts aresubjected to both bending and torsional loads.Thus, their fatigue characteristics follow thebending/torsional fatigue breakdown line.

Gears are subjected to both surface loads andbending loads. Lightly loaded gears tend to sufferdamage from surface fatigue. As the loadincreases, the damage changes from surface tobending fatigue. Heavy loads on the gear teeth

will cause bending fatigue damage.The two causes of fatigue damage to the carrierassembly are:

r

Exceeding the GVW/GCW rating of the carrier

r

Operating the vehicle at a weight that exceedsthe carrier’s GVW/GCW rating reduces thefatigue life of the components. The rated GVW/ GCW of a carrier changes with the road gradeand surface. As the grade increases, so does thetorque (load) required to move the vehicle.Likewise, as the road surface changes fromhard to soft, the rolling resistance increases andmore torque is needed. Again, as the loadincreases, fatigue life of the componentsdecreases.

Housing Overload

The main contributor to axle housing damage isstructural or operational overload. This takes placewhen the vehicle is loaded in excess of the platedGross Axle Weight Ratings (GAWR). When theGross Axle Weight (GAW) increases, axle housinglife decreases. Figure 2.4

. Axle housing life isvirtually infinite if the load is at the plated GAWR.

Figure 2.3

Figure 2.4

BENDING/TORSIONAL FATIGUE

MANYFEW

SMALL

LARGE

BREAKDOWN LINE

LOAD

NUMBER OF CYCLES

ENDURANCE LIMIT

AXLE HOUSING LIFE VS

GROSS AXLE WEIGHT

LONGSHORT

LIGHT

HEAVY

GAW

LOAD

AXLE HOUSING LIFE

GAWR


37/91


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34

Figure 2.5a Figure 2.5b

Figure 2.5c Figure 2.5d

Figure 2.5e Figure 2.5f

INTER-AXLE DIFF. ACTION

MAIN DIFF. ACTION



MAIN DIFF. ACTION


MAIN DIFF. ACTION

MAIN DIFF. ACTION

MAIN DIFF. ACTION


39/91


35

Potential DifferentialSpinout Scenarios

Backing Under a Trailer

When a tractor is backing under a trailer,particularly one on which the landing gear is toolow, the extra effort could cause loss of tractionbetween the tire and the ground. The resultingdifferential spinout is most likely to happen on wetand slippery pavement or on unpaved surfaces.Figure 2.6

.

Starting on a Slippery Surface

Differential spinout damage can and often doesoccur when the vehicle is started on a wet orslippery surface. It is especially likely to happenwhen the vehicle is bogged down in mud or snowand the driver attempts to work it free by steppingon the throttle and “burning out.” Figure 2.7

.

Traveling on a Slippery Surface

Any moving vehicle encountering a wet orslippery surface can lose traction and result indifferential spinout. This usually happens whendriving up a hill because of the additional torquerequired to negotiate the grade. Figure 2.8

.

In all these situations that result in spinouts,certain assemblies are subject to damage. Theyare:

r

IAD (sometimes called a power divider).

r

Main differential.

To prevent differential spinout damage, mostMeritor tandem drive axles are equipped with IADlock outs. Most Meritor drive axles can also bespecified with main differential locks. Refer toMeritor service and operation materials foradditional information on traction control.

Figure 2.6

Figure 2.7

Figure 2.8

SLIPPERY SURFACE

SLIPPERY SURFACE


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36

Typical Shock Load Damage

Shock damage is another common type of axlecomponent damage. It can be defined as onewhich results from a rapidly applied load, force or

torque severe enough to exceed the strength ofthe axle shaft or carrier components.

Depending on the severity of the shock to the part,the final component failure may not occur untilmany miles later.

There are a number of operating conditions whichcan result in shock load damage:

a. Backing under a trailer. Figure 2.9

.

b. Hitting dry pavement with a spinning wheel.Figure 2.10

.

c. Missing a shift. Figure 2.11

.

d. Popping the clutch. Figure 2.12

.

e. Locking the inter-axle or main differentialduring a spinout. Figure 2.13

.

f. Improper use of creeper gears. Figure 2.14

.

Backing Under a Trailer

Backing under a trailer, particularly if the landinggear is too low, can shock the entire drivetrain.This happens most often when the trailer is loadedand the tractor is rammed back. By resisting theaction of the moving tractor, the trailer causes therotating parts of the drivetrain to stop while the

engine is still applying torque to keep themmoving. This rapidly applied torque, if severeenough, can cause damage to the carrier or otherdrivetrain components. Figure 2.9

.

Hitting Dry Pavement With aSpinning Wheel

This condition can cause a severe shock load inthe axle and drivetrain. When the wheel isspinning, the axle components are rotating at highspeed. As the wheel contacts a dry surface or onewith greater traction, it slows down very rapidly. Ifthe deceleration is great enough, forces sufficientto exceed the strength of the axle may result, andcause component damage. Figure 2.10

.

Figure 2.9

Figure 2.10

DRY

PAVEMENT

SLIPPERY

SURFACE


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37

Missing a Shift

Recovering from a missed shift can cause shockloading and axle damage. Figure 2.11

.

Popping the Clutch

If the wrong transmission gear is selected to startthe vehicle, there may not be enough torqueavailable at the wheels. In this situation the drivermay speed up the engine and rapidly release theclutch, rather than shifting to a lower gear. Thisaction, called popping the clutch, frogging orhumping the vehicle, induces a rapidly appliedload in the drivetrain, and can result in shock loaddamage. Figure 2.12

.

Locking the Inter-Axle or Main DifferentialDuring a Spinout

Any attempt to lock the IAD when the wheels arespinning can cause severe damage to the clutchcollar and mating shaft splines, as well as to othercarrier components. If a wheel is slipping, thedifferential should not be locked until the wheelspeed is stopped.

Any attempt to lock IAD or main differential whilethe wheels are spinning (losing traction) can causedamage. Figure 2.13

.

Figure 2.11

Figure 2.12

Figure 2.13

DIFFERENTIAL

TRACTION

GOODPOOR

UNLOCKLOCK


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38

DCDL Lock Profile

The IAD divides the power equally between thetwo axles of a tandem and does not allow the totaltorque of both axles to exceed twice the torque of

the axle with the lower amount of tractive effort.The IAD lock mechanically deactivates theIAD, allowing the forward and rear drive axles toprovide maximum traction. The Driver-ControlledDifferential Lock (DCDL) deactivates the maindifferential, providing maximum traction potentialfrom each wheel end of the axle.

Operation Tips — DCDL

1. The DCDL can be locked or unlocked if thevehicle is standing still, or moving at aconstant, low speed when the wheels are notspinning, slipping or losing traction.

2. When the DCDL is locked, the vehicle turningradius increases. This condition is called“understeer.” Always exercise caution, usegood judgment and drive at low speeds (under25 mph) when the DCDL is locked.

3. Always unlock the DCDL as soon as maximumtraction is no longer needed and the vehicle istraveling on a good road or highway.

4. Do not lock the DCDL when:

r

The wheels are slipping or losing traction.Doing so may result in axle damage.

r

The vehicle is traveling down steep grades.This may reduce vehicle stability and causethe tractor and trailer to jackknife.

Operation Tips — IAD

The IAD is controlled by the driver.

1. Keep the IAD switch in the UNLOCK positionunder normal operating conditions, with goodtraction.

2. For improved traction, lock the IAD whenapproaching or anticipating icy or poor drivingconditions.

3. Always unlock the IAD when improvedtraction is not needed and when the vehicle ison a good road or highway.

4. After locking or unlocking the IAD, let up onthe accelerator to provide an interruption intorque to the drivetrain. (Activating the IADlock is similar to shifting a manualtransmission with a clutch.)

5. Do not actuate the IAD switch while one ormore wheels are actually slipping, spinning orlosing traction. This may cause damage to theaxle.

6. Do not spin the wheels with the IAD unlocked.This may cause damage to the axle.

NOTE: For additional information on tractioncontrol, contact Meritor‘s Customer Service Centerat 800-535-5560.


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39

Improper Use of Creeper Gears

Main transmission creeper gears are designed forspecialized very low speed vehicle control orpositioning. Creeper gears are not typically used

during normal highway vehicle operation. If usedfor high torque transfer, shock loading damagemay result to the axle carrier, drive shafts ordriveline components. Figure 2.14

.

If severe enough, shock loads can cause instantfailure of the part. Less severe shock loads cancreate a crack or point of origin from whichbending or torsional fatigue can start, even undernormal or reduced loads. No matter how small,these cracks can result in fatigue within only a fewload cycles.

Figure 2.14


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40

Maintenance and Rebuilding

Improper maintenance is another source of axledamage. Regardless of how well the vehicle isdesigned and correctly operated, if it is not

properly maintained at required service intervals,premature axle component wear will occur,eventually leading to failure.

Some premature component damage to the driveaxle carrier originates from improper rebuildingpractices. Component damage of this kind can beavoided when mechanics know the correctmethods, have the proper replacement parts andtools, and exercise care when rebuilding thecarrier.

It is important for the professional technician tounderstand that there are a number of serviceoperations that do not require removal of the

carrier from the axle housing.

A carrier does not

have to be removed from theaxle housing to:

1. Replace a leaking pinion seal

2. Change lubricant

3. Replace breather assembly

4. Adjust input and/or through shaft endplay ofthe forward tandem axle carrier

A carrier may

have to be removed if one or moreof the following symptoms are present:

1. Trucks with tandem drive axles will move onlywhen IAD is locked or engaged

2. Differential makes noise

3. Contaminated lubricant (i.e., silveryappearance, metal pieces suspended in lubeor presence of water contamination).

4. High operating temperatures that have beenverified

5. Carrier casting broken, holes in case, etc.

6. Leak condition exists that is not caused by aseal leak

7. Excess end play on hypoid pinion

Maintenance andRebuilding Practices

The following actions are recommended to avoidsome of the more common problems that ariseduring rebuilding:

Proper Tightening of Fasteners

The correct fastener torque values for satisfactorycarrier life are determined by extensiveengineering testing and can be assured only withthe use of torque wrenches. Maintenance manualscontaining these torques are available forrebuilding operations.

Install Yokes Correctly

Most mating shafts for driveline yokes on current

production carriers have a helix lead on the splinewhich requires that the yokes be pressed on andproperly seated.

Use Proper Tools

The use of proper tools during the rebuild cannotbe stressed too much. The price of a special tool issmall compared to the cost of a carrier componentdamage that results from improper rebuilding.

Use Genuine Meritor Parts

Meritor genuine service parts are manufactured to

the same exacting specifications as the originalcomponents. “Will fit” parts may be lessexpensive initially, but may not providecomparable performance and could result inpremature component failure, which is far moreexpensive than the initial cost of quality parts.

Follow Maintenance Manual Procedures

Meritor has a full line of maintenance manuals.Appropriate cautions and proper tools to be usedare also carefully spelled out. Manuals and wallcharts are available from Meritor. ContactMeritor’s Customer Service Center at800-535-5560.


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41

Lubrication-RelatedComponent Damage

Another cause of axle component damageoriginates with the lubricant, or with lubricantchange practices. The lubricant which protects theaxle components has three key functions:

r

To reduce friction between parts,

r

To carry heat away from parts, and

r

To carry dirt and wear particles away fromparts.

When lubricated component damage occurs, it isgenerally the result of improper maintenance andhas its roots in one of three basic problem areas:

r

Low lubricant level

r

Improper type of lubricant or lubricant withdepleted additives

r

Contaminated lubricant

A closer look at these maintenance problem areasfollows:

Low Lubricant Level

When the lubricant level in an axle is too low, thefriction between the parts generates heat andcauses temperatures to increase considerably. Ifthe temperatures become high enough, the partsmay be harmed.

Low lubricant levels can result from inadequaterefilling, or from leaks. Figure 2.15

. MaintenanceManual 1, Lubrication,

gives the correct oilvolumes for Meritor drive axles. Please note that acommon cause of leaking seals stems from aclogged axle housing breather. Be sure to cleanand check the axle breather function before doingfurther work on the axle wheel or shaft seals.

Improper Type of Lubricant or LubricantWith Depleted Additives

Use of improper lubricant or lubricant withdepleted additives is a major cause of gear set

damage. Meritor axles require lubricants that havea GL-5 level of EP (extreme pressure) additivesbecause of the sliding and rolling action of hypoidand spiral bevel gears. Gear lube that is notformulated for use with these types of gears willnot provide adequate service life, and prematurecomponent wear or damage will occur. MeritorAutomotive Maintenance Manual 1, Lubrication,

contains specification references for the correctaxle lubricant.

Contaminated Lubricant

Another common cause of axle damage iscontaminated lubricant. This is defined aslubricant which contains water, dirt, or wearparticles.

Lubricant can become contaminated by:

r

Water and dirt entering the carrier through afaulty wheel or shaft seal, the carrier-to-housingjoint or the axle housing breather.

r

Wear particles generated from normal orabnormal vehicle service.

Meritor axles contain magnetic drain plugs and

magnets as a standard feature. These magnetsisolate metallic particles as they settle to thebottom of the axle housing.

In addition, Meritor offers tandem axles thatincorporate oil pumps. This system providespressurized lubrication. A spin-on oil filterremoves contaminants from the lubricant. It is stillessential to always follow the recommendedschedule for lubrication changes. Refer toMaintenance Manual 1, Lubrication

.

Figure 2.15

Oil level must be even withbottom of fill plug hole.

FILL PLUG


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42

Tire Matching

For optimum tire life, Meritor recommendsmatching the tires to within 1/8-inch of the samerolling radius and 3/4-inch of the same rolling

circumference. In addition, the total tirecircumferences of both driving axles should bematched to each other as nearly as possible. Thiswill help to ensure optimum life of both tires andaxles. Figure 2.16

.

Procedure

The vehicle should be on a level surface andcarrying a properly distributed rated capacity load.Make sure that all tires are the same size. Measurenew tires to confirm that they are correctlymatched.

1. Inflate all tires to the same pressure.

2. Carefully measure the rolling circumference ofeach tire with a steel tape.

3. Mark the size on each tire with chalk. Thenarrange them in order of size, from largest tosmallest.

4. Mount the two largest tires on one side of oneaxle and mount the two smallest on theopposite side of the same axle.

5. Mount the four tires on the other axle in thesame way.

6. Test run the vehicle to obtain accurate rear

axle lubricant temperature readings on thetwo axle lubricant temperature gauges.

7. Vary tire air pressure (within the tiremanufacturer's recommended range) so thetemperature of both axles is within 30˚F ofeach other and no higher than 220˚F. Thishelps to ensure uniform loading and optimumlife of the tires.

Figure 2.16

Total tire circumference of one drive axle should equaltotal tire circumference of other drive axle.

Match tires of each axle:• to 1/8" of same radius• to 3/4" of same circumference


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43

Torsional Vibration

Torsional vibration results from several factors,most notably the power characteristics of today'shigh-efficiency diesel engines, which can run at

lower rpm. It can be difficult to detect because thedriver is often well isolated within the cab. Atcertain speeds, however, the driver may notice alow-frequency growl or the rearview mirrorshaking, which may be signs of torsionalvibration. If unchecked, torsional vibration canlead to major damage or total failure of the axlecomponents.

Axle components are generally less susceptible todamage from torsional vibration than othercomponents in the powertrain. Some tandemaxles have experienced loosened nuts at the inputend and yoke wear, but most of these problems

have been resolved through the manufacturingprocess. Tandem axle power dividers, however,have shown component wear which may haveresulted from vibration. Meritor recommendsusing an axle pump to supply increasedlubrication to axle gears and offset some vibrationproblems. Single axles have larger rotatingcomponents and thus experience fewer vibration-related problems. Check any noises coming fromthe rear of the vehicle. These could either be axlenoises or warnings of driveline vibration.

Vehicle or Powertrain Modifications

Modifications to vehicle configuration can result inpremature failure or unsafe operating conditions.These changes include but are not limited to:

r Horsepower

r Torque

r Vocation

r Suspension

r Transmission or axle ratio

r Retarders

r Tire size

Meritor Automotive must be consulted prior tothese modifications.


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CAGE DAMAGE

Cage Deformation —Improperly installed ordropped bearing.

Rollers binding and skewing —Cage ring compressed duringinstallation or interferenceduring service.

HIGH SPOTS INCUP SEATS

Localized spalling on the cuprace from stress riser createdby split housing pinch point.

FOREIGNMATERIAL

Bruising — Debris from otherfatigued parts, inadequatesealing or poor maintenance.

Abrasive wear — Fine abrasiveparticle contamination.

Grooving — Large particlecontamination imbeddinginto soft cage material.

CORROSION/ ETCHING

Etching — Rusting withpitting and corrosion frommoisture/water exposure.

Staining — Surface stain withno significant corrosion from

moisture exposure.

Line spalling — Roller-spacedspalling from bearingsoperating after etchingdamage.


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FALSE BRINELLING

TRUE BRINELLING

Wear causedby vibrationor relativeaxial movementbetween rollers and races.

Damagefrom shockor impact.

ELECTRIC CURRENT

Fluting —Series of small axialburns caused by electriccurrent passing through thebearing while it is rotating.

Electric arc pitting — Smallburns created by arcs fromimproper electric groundingwhile the bearing isstationary.

IMPROPER FIT

Cone bore damage —Fractured cone due to out-of-round or oversized shaft.

Cup spinning — Loose cup fitin a rotating wheel hub.

PEELING

Micro-spalling due to thinlubricant film from highloads/low RPM or elevatedtemperatures.

MISALIGNMENT

Irregular roller path from

deflection, inaccuratemachining or wear of bearingseats.


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Section 3Damaged Axle Review

44

Section 3Damaged Axle ReviewIdentifying Axle Damage

The most common causes of axle damage are:

r

Spinout

r

Shock

r

Fatigue

r

Lubrication

Many of the resulting types of damage can beidentified through simple visual inspection. Thephotographs in this section show actual damagedcomponents to help technicians and operatorsidentify signs of current and potential problems.

It is important, however, to accurately identifyprimary and secondary damage, as well as theircauses. This requires following effective, logicalfailure analysis techniques. To aid in this process,this section explains what signs to look for andcategorizes them as primary or secondary. Redand yellow arrows identify primary and secondarydamage respectively. The text also providessuggestions for resolving the immediate problemand for preventing future breakdowns.

A Meritor Automotive District Service Managercan also assist you in identifying specificcomponent problems, recommend correctiveaction and arranging appropriate technician and/ or driver training.


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45

Bearing Adjusting Ring

Visual Conditions

r

Drive pinion teeth are fractured in root beamfatigue mode. (Primary) Figure 3.1

.

r

The flange side adjusting ring shows partingmarks at the cap-to-case area. (Secondary)Figure 3.2

.

r

The cotter pin on the main differential bearingcap for the adjusting ring is bent outward.(Secondary)

Primary Cause of Damage

Drive pinion teeth are segmented due to fatigue.(Primary) Broken teeth jammed in ring gear

forcing the main differential to thrust the adjustingring outward. This sequence of events issupported by evidence of bent pin and partingmarks on adjusting ring threads.

NOTE: Generally, adjusting ring damage issecondary to some other root cause of carrierdamage.

Preventive Actions

Operate vehicle within design specifications.

Part Code: Gear, Pinion

Condition Code: Root Beam Fatigue

Figure 3.1

39367d10

Figure 3.2

39203d07

1. Bent cotter pin

2. Stripped teeth


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46

Drive Pinion

Visual Conditions

r

Three adjacent gear teeth are broken. (Primary)Figure 3.3

.

r

The adjusting ring has been pushed completelyout of carrier cap assembly. (Secondary)

r

The cotter pin is bent 90 degrees from adjustingring movement. (Secondary) Figure 3.4

.

r

Dark parting marks are present on the adjustingring where the ring was clamped between themain differential bearing cap and the carriercase. (Secondary) Figure 3.5

.


The original drive pinion tooth fracture wasinduced by a moderate shock load. The fracturepropagated in fatigue until failure occurred. Thesheared adjusting ring teeth and bent cotter pinwere induced by the severe separation thatoccurred when the loose tooth went through gearmesh. Figure 3.3

.

Preventive Actions

Operate vehicle according to design-rated weightlimits.



Figure 3.3

39278d14

Figure 3.4

39218d20

Figure 3.5

29251d20


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47

Drive Pinion Gear

Visual Conditions

r

Pinion teeth are broken off at the heel of thedrive pinion gear. (Primary) Figure 3.6

.

r

Ring gear teeth may have secondary damage.Figure 3.7

.


Position error between ring gear and drive pinion.This is supported by the observation that thefracture origins are on the heel of the three brokenpinon teeth.

Preventive Actions

Incorrect maintenance or rebuild practices. Referto the appropriate maintenance manual.

Part Code: Further investigation is required.Primary cause of failure will determine propercodes.

Condition Code: Identify primary cause todetermine code.

Figure 3.6

JIM USE 22 OR 23

Figure 3.7

39217d01

1 Original pattern

2 Secondary pattern


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48

Drive Pinion Gear

Visual Conditions

r

The ring gear is worn to knife-like edges,indicating extreme premature wear.(Secondary) Figure 3.8

and Figure 3.9

.

r

The drive pinion gear premature wear is sosevere that the hardened tooth surfaces havebeen worn away to the point that they nolonger mesh with the ring gear. Figure 3.8

.

r

Little evidence of heat, fairly clean gear set, andno burnt lube indicate incorrect lube, metaldebris present.

r

Check vehicle lubricant change history.


Axle lubricant did not meet GL-5 specifications orhad exhausted its EP additive package creating theexcessive drive pinion and ring gear wear.

Preventive Actions

Maintain scheduled intervals for lubricationmaintenance. Refer to Maintenance Manual 1,Lubrication

.

Part Code: Lubricant

Condition Code: Incorrect

Figure 3.8

30213d08

Figure 3.9

PC PHOTO 39192-45


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49

Drive Pinion RootBeam Fatigue

Visual Conditions

r

Drive pinion gear teeth are broken off with deeproot bending fatigue beach marks. (Primary)Figure 3.10

and Figure 3.11

.

r

Ring gear teeth damage is secondary.Figure 3.10

.


Drive pinion has signs of overloading. The brokenpinion teeth have beach marks starting at theroots. Pinion teeth were moderately overstressedfor a period of time, but one final load event

caused the three beach-marked teeth tocompletely break away from the shaft.

Preventive Actions

Operate vehicle according to design rated limits.



Figure 3.10

39218d02

Figure 3.11

PC PHOTO 39217-13

1 Ratchet marks

2 Beach marks

3 Marred area

4 Final fracture


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50

Driveline/TorsionalVibration Issues

Visual Conditions

r

Flattened to concave wear pattern on bevelteeth of side gear and IAD pinions. Figure 3.12

.

r

Output shaft and side gear spline wear.Figure 3.12

and Figure 3.13

.

NOTE: These conditions are often accompaniedby looseness of the U-joint or previoustransmission synchronizer pin service.


Incorrect driveline angles, driveline U-joint is out

of phase, unbalanced driveline, bent driveline orincorrect suspension height.

Preventive Actions

Perform action checklist:

r

Driveline inspection

r

Driveline repair/adjustment

r

Suspension adjustment

Part Code: Gear, Rear Side IAD

Condition Code: Bevel Teeth Worn

Figure 3.12

39367d40

Figure 3.13

Documents

Analisis de Fallas Ejes Meritor