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309

Chapter 16Rear Axle AssemblyConstruction andOperation

Technical Terms

Solid-axle rear suspension

Independent rear suspension

Differential drive gears

Drive pinion gear

Pinion bearing

Collapsible spacer

Jam nut

Pinion shim

Ring gear

Wheel hop

Standard differential

Differential case

After studying this chapter, you will be able to:� Explain the purpose of a rear axle assembly.� Identify the major parts of a rear axle assembly.� Describe the differential drive gears and related parts.� Calculate rear axle ratio.� Compare differential and rear axle assembly design variations.� Describe the operation of a standard differential and of the various types of locking differentials.

Spider gears

Side gears

Locking differential

Limited-slip differential

Clutch-plate differential

Cone differential

Ratchet differential

Torsen differential

Hydraulic locking differential

Differential carrier

Axle tube

Removable carrier

Pinion pilot bearing

Side bearings

Integral carrier

Solid drive axle

Axle flange

Axle bearing

Axle collar

Axle retainer plate

Semi-floating axle

Axle shim

Full-floating axle

Independently suspended drive axle

This sample chapter is for review purposes only. Copyright © The Goodheart-Willcox Co., Inc. All rights reserved.

Introduction

The rear axle assembly is used on rear-wheel drivevehicles. This assembly is the final leg of the drive train. Itis often called the final drive or rear end. The rear axleassembly is often mistakenly called the differential. Thedifferential is only part of the rear axle assembly.

The basic design of rear axle assemblies has beenadopted by all manufacturers for many years. There areseveral variations, but all operate according to the samebasic principles. The major difference between rear axleassemblies depends on whether the vehicle has solid-axlerear suspension or independent rear suspension. Solid-axlerear suspension incorporates rigid and nonflexing driveaxles and axle tubes; both wheels move as one solid unitin response to bumps and potholes. Independent rearsuspension incorporates jointed drive axles (no axle tubes)that allow for flexibility and independent axle movement.

This chapter is designed to identify and explain the con-struction and operation of various rear axle assemblies. Thematerial in this chapter provides a basis for understandinghow to properly troubleshoot and repair rear axle assemblies.

Construction and Operation Overview

The rear axle assembly includes the differentialassembly, the rear drive axles, and the rear axle housing.Rear axle assemblies are subjected to heavy loads from the

engine and road. They are ruggedly constructed andseldom fail. The most common rear end failures are axlebearing failures. A typical rear axle assembly is shown inFigure 16-1.

In a rear axle assembly, engine power enters the drivepinion gear from the drive shaft assembly and differentialpinion yoke/flange. The drive pinion gear, which is inmesh with the ring gear, causes the ring gear to turn. Theinteraction of the ring and drive pinion gears turns thepower flow at a 90° angle. The difference in the number ofteeth on the ring and pinion gears causes a reduction gearratio. This reduces turning speed, while increasing torque.Power from the ring gear flows through the differentialcase, spider gears, and side gears to the drive axles. Thedrive axles transfer power from the differential assembly tothe rear wheels.

The bearings and rear axle housing are key com-ponents of the rear axle assembly. They are designed tosupport and align the differential assembly and the driveaxles. Notice that the bearings and axle housing are large,heavy-duty parts. This is to ensure they will stand up underhard usage.

Seals and gaskets are also very important to theoperation of the rear axle assembly. Seals are used at thedifferential pinion yoke/flange and at the outer drive axles.Gaskets are used at housing interfaces, such as betweenthe differential cover and the housing, to provide a tightseal from the outside.

Figure 16-2 is an exploded view of a common type ofrear axle assembly. Notice the relationship of the internalparts to the housing and to each other. Note that the rear

310 Manual Drive Trains and Axles

Wheel, oraxle, bearing

Axle sealAxle

flange

Sidebearings

Differentialcase

Inspection cover

Ring gear

Drive axlePinion

bearings

Companionflange

Drivepinion gear

Pinion orspider gears

Side gears

Rear axlehousing

Driveaxle

Figure 16-1. Most rear axle assemblies contain the same parts as shown in this cutaway. Note that some drive axles differ from thisbasic design. (Ford)

Chapter 16 Rear Axle Assembly Construction and Operation 311

Bolt

Inspection cover

Thrustwasher

Spidergear

Retainingwasher

Side gear

Thrust washer

Thrustwasher

Sidegear

Pinion shaftlock pin

Shim

Cup

Sidebearing

Pinionshaft

Spidergear Thrust

washer

Sidebearing

Cup

Shim

Drivepinion gear

Ring and pinionassembly

Pinionshim

Bolt

Bolt

Differential case

Differentialcap

Pinionbearing

Pinionbearing cupBolt

Differentialcarrier

Rear axlehousing

Axle tube

Filler plug

Bearingcup

Pinionspacer

Pinion bearingassembly

Pinion seal

Pinion nut

Pinionflange

Slinger

Bolt

Axlebearing

SealNut

Driveaxle

Ring gear

Brake assembly

Figure 16-2. Exploded view of a rear axle assembly shown in Figure 16-1. (Ford)

axle housing and drive axle designs will be different whenthe vehicle has independent rear suspension. Also, whenthe rear axle assembly is equipped with a limited-slipdifferential, it will contain more parts. These features willbe discussed later in this chapter.

Differential Assembly

The differential assembly in a rear-wheel drive vehiclehas three functions. The first, and most obvious, is toredirect the power flow to drive the rear wheels. Thepower flow must make a 90° turn between the drive shaftassembly and the rear wheels. This is accomplished in thedifferential assembly by the drive pinion and ring gears.

The second function of the differential assembly isto multiply engine power, reducing speed at the outputin the process. If there were no gear reduction (1:1 gearratio), the vehicle would accelerate very slowly. In somecases, the engine would be unable to move the vehicle.At the very least, gas mileage would be harmed, sincethe engine would not reach its most efficient rpm range.For this reason, the ring and drive pinion assembly, bydesign, provides a reduced speed at its output. Thereduction is between 2:1 and about 5:1, depending onthe engine size, vehicle weight, and intended use of thevehicle.

The third function of the differential assembly is toallow the vehicle to make turns. If the assembly did notmake allowances for the different speeds of the rear wheelsduring turns, one tire would lose traction with the groundas the vehicle turned corners. The differential assemblyallows the vehicle to make smooth turns.

The differential assembly consists of numerous parts,including the differential drive gears (ring and drivepinion gears), pinion bearings, differential case, spiderand side gears, and side bearings. See Figure 16-3. Theseparts and their function are described in detail in thefollowing section.

Differential Drive GearsThe differential drive gears also called the ring and

pinion gearset, consist of the ring and drive pinion gears,Figure 16-4. These hypoid gears redirect power flow by90° and multiply engine power. The number of teeth in thering gear compared to the number of teeth in the drive pin-ion gear sets the rear axle ratio. For instance, if the ringgear has 40 teeth and the pinion gear has 10 teeth, theratio is 40:10, or 4:1. The ring gear always has more teeththan the drive pinion gear. Rear axle ratios can always bedetermined by dividing the number of teeth on the ringgear by the number of teeth on the drive pinion gear.

Drive pinion gearThe drive pinion gear is a hardened-steel gear with an

integral shaft, Figure 16-5. It is machined to mesh with androtate the ring gear. The end of the shaft opposite the gearhas external splines that fit the internal splines of the differ-ential pinion yoke/flange. The gear is supported by twotapered roller bearings, called pinion bearings.

By design, the axial centerline of the drive pinion gearlies below that of the ring gear. With this design, the piniongear is placed lower in the rear axle housing. This is doneto lower the drive shaft and, therefore, the drive shaft humpin the vehicle passenger compartment. The spiral design ofthe gear teeth allows the gears to mesh with a slidingmotion, creating a smooth power transfer. As a result of thesliding action, the gears must have a good supply of theproper lubricant. Gears of this type are called hypoid gears.


Pinion bearing

Drivepinion gear

Adjustingnut

Sidebearing

Side gearsRing gear

Spidergears

Differentialshaft

Case

Side bearingAdjusting

nut

Figure 16-3. Relative positions of parts of a differential assembly.The interaction of the various parts of the differential may bemore easily understood by studying this illustration. (Subaru)

Rear axlehousing

Pinionpreload shim

Differentialpinion yoke

Pinionbearings

Pinion depth shim

Drivepinion gear

Ringgear

Sidebearing

Differentialcase

Differentialbearing shims

(endplay/preload)

Sidebearing

Figure 16-4. The positions of the drive pinion gear and the ringgear are always about the same. The two pinion bearings andtwo side bearings are always tapered roller bearings that mustbe carefully adjusted. Some drive pinion gears have a thirdbearing—a pinion pilot bearing—for support. Bearings andadjusting devices (shims or adjusting nuts) are usually locatedas shown. (DaimlerChrysler)

The rear pinion bearing is pressed onto the drivepinion gear shaft at the gear end. The front pinion bearingis often a slip fit on the smaller end of the shaft. The outerraces, or bearing cups, of both bearings are pressed intothe rear axle housing.

Either a solid spacer or a collapsible spacer (crushwasher) is used to set the pinion bearing preload. Thecollapsible spacer is designed to be slightly compressedwhen the drive pinion gear is installed in the rear axlehousing. The spacer maintains a mild pressure betweenthe front and rear pinion bearings, making it possible toaccurately adjust the bearing preload.

The differential pinion yoke/flange has internalsplines that fit the external splines on the drive pinion gearshaft. See Figure 16-6. The rear of the yoke/flange, whereit fits into the rear axle housing, is machined smooth. Thisis the sealing surface for the pinion seal. The yoke/flange is

held to the drive pinion gear shaft by a large nut and washerthat threads onto the shaft. This nut is a type known as ajam nut. The top threads of the nut are deformed to tightlygrip the threads on the drive pinion gear shaft. This is aninterference fit. Tightening the nut also adjusts the pinionbearing preload.

The pinion yoke is machined to accept the bearingcups of the rear universal joint. The cups are either pressedin and held with snap rings, or they are attached to theyoke with U-bolts or bolted-on straps.

Pinion flanges are simply a two-piece yoke joined bymating flanges. The outer section has the yoke; the innersection has the external splines for the pinion gear shaft.These companion flanges, as they are also called, wouldbe separated at the flanged section to remove the driveshaft assembly, Figure 16-7.

The position of the drive pinion gear relative to thering gear must be set exactly. Otherwise, the gears will benoisy and will wear out quickly. The position of the drivepinion gear in the housing must be carefully adjusted sothat it contacts the ring gear at exactly the right toothdepth. To make this adjustment to the ring and drive pinionclearance, a pinion shim is installed in the housing, behindthe rear bearing cup. The thickness of this shim determinesthe depth of the drive pinion gear in the housing. This shimis installed at the factory when the rear end is assembled.It must be checked for proper thickness whenever the drivepinion gear is removed.

Figure 16-8 shows the position of the pinion shim onmost rear axle assemblies. This figure also shows the rela-tive position of the collapsible spacer.

Ring gearThe ring gear, Figure 16-9, transfers power from the

drive pinion gear to the differential case. Both the ring gearand the case are machined to fit together tightly. Bolts are


Threads foryoke nut

Drive pinionsplines

Collapsiblespacer

Drive pinion gear

Rear pinionbearing

Drive piniongear shaft

Figure 16-5. A typical drive pinion gear. The rear pinion bear-ing is pressed on the drive pinion gear shaft. A collapsiblespacer is used to aid in pinion bearing installation. Threads andsplines at the front of the drive pinion gear shaft are used forinstalling the differential pinion yoke. (General Motors)

Differentialpinion yoke Differential

seal surfaceSplines lockgear to yoke

Drivepinion gear

Drive piniongear shaftFlat washer

Piniongear nut

Hole forU-joint

Figure 16-6. The differential pinion yoke slides over the drivepinion gear shaft and is secured by the pinion gear nut. Thetightening nut also preloads the pinion bearings. The outer sur-face of the drive pinion gear shaft seals against the front oil seal.

U-joint

Rear axleassembly

Companionflanges

Flange bolts

Drive shaft

Figure 16-7. Some differential pinion yokes are two-pieceflanged assemblies, as shown here. This type of design isreferred to as a differential pinion flange, or companion flange.(Ford)

used to hold the ring gear to the case. The bolts passthrough holes in the case and are threaded into tappedholes in the back of the ring gear.

Since the ring and drive pinion gear teeth must meshaccurately to transmit motion without noise or damage,the position of the ring gear is important. Automotive tech-nicians should be familiar with gear terminology that willbe encountered while adjusting the differential assembly toobtain correct gear positions. The convex side, or driveside, and the concave side, or coast side, of the ring gearare pointed out in Figure 16-9A. These terms will be usedwhen differential gears are adjusted. The tooth parts thatmust be carefully adjusted are identified in Figure 16-9B.The terms heel and toe will be used extensively for ringand pinion gearset adjustment.

Differential Case AssemblyWhen a vehicle makes a turn, the outer wheel travels

a greater distance than the inner wheel—the arc (orradius) of the turn is greater at the outer wheel. If the reardrive axles were simply connected together, both wheelswould have to travel an arc of the same length during aturn. Since this is impossible, one of the tires would losetraction, or slip, during the turn. If the tire did not slip, itwould skip over the road surface. This condition is calledwheel hop.

The purpose of the differential case assembly is toallow the vehicle to make turns without slippage or wheelhop. It does this with an arrangement of gears that allowsthe rear wheels to turn at different speeds. Two basic typesof differential case assemblies used to accomplish this taskare the standard differential and the locking differential.

Standard differentialThe standard differential, also called a single-pull

differential, is composed of meshing spider and side gearsenclosed in a differential case. See Figure 16-10.

The standard differential case is usually a one-pieceunit. The ring gear is bolted to the case. The case is usuallymade of cast iron. Occasionally, it is made of aluminum.Side bearings are usually pressed onto the case.

The spider gears are made of hardened steel and areheld in place by a steel shaft called the pinion shaft. Thepinion shaft passes through the differential case and thecenter of the spider gears. It is attached to the case with abolt. Spider gears are also called pinion gears.

Spider gears mesh with side gears, which are alsomade of hardened steel. When the ring gear and differen-tial case turn, the spider and side gears also turn. Powerflow is through the case, into the spider gears, and on intothe side gears. The side gears are splined to the drive axles.


Rear U-jointFront pinion

bearing Pinionshim

Piniongear nut

Differentialpinion yoke

Collapsiblespacer

Rear pinionbearing

Figure 16-8. Pinion shim and preload spacer locations. Properpinion adjustment is critical. The adjusting nut, preload spacer,and depth shim are all critical to proper pinion adjustment.(DaimlerChrysler)

Correctpattern

Toe

Concave side(coast)

Convex side(drive)

HeelTop land

Profile

Root

Toe

Heel

Lengthwisebearing

arc

A B

Figure 16-9. When installed, the ring gear is bolted to the differential case and meshes with the drive pinion gear. A—The ring gearhas convex and concave sides. The convex side is the drive side. It contacts the drive pinion gear when the vehicle is accelerating.The concave side is the coast side. It contacts the drive pinion gear when the vehicle is decelerating. B—Gear terminology will beimportant when the differential assembly is serviced. Proper heal and toe contact is critical to quiet operation and long life.(General Motors, DaimlerChrysler)

They transfer power to the drive axles and rear wheels.Side gears are also called axle end gears.

Some heavy-duty differentials contain four spidergears and two pinion shafts. In this design, there is a centerhole in one of the shafts. The other shaft passes through it.The side gears are splined to the drive axle. On somedifferentials, the side gears contain C-locks, which holdthe axles in place. See Figure 16-11.

The spider and side gears are bevel gears. Powertransfer through the bevel gears causes them to be forcedaway from each other. This causes high thrust forces on thebacks of the gears, where they contact the differential case.Hardened-steel washers are usually installed between theback of the gears and the case. These washers provide asliding surface and reduce wear. See Figure 16-12.

Figure 16-13 shows the operating states of the differ-ential while driving straight ahead and while drivingaround a corner. In Figure 16-13A, the vehicle is movingstraight ahead and both wheels are traveling at the samespeed. The spider and side gears rotate with the case butdo not move in relation to it. The entire case assemblyrotates as a unit.

When the vehicle makes a turn, the axles and the sidegears begin turning at different speeds. The outer wheel—the left wheel, in the case of a right turn—turns faster thanthe inner wheel, and the left side gear turns faster than theright side gear. See Figure 16-13B. As a result of thedifferent axle speeds, the spider gears begin to rotate. Theleft side gear, which is moving faster than the right sidegear, drives the spider gears, causing them to rotate on, orwalk around, the right side gear.

Note that the differential case speed on turns is theaverage of the side gear speeds. This is because one sidegear is rotating faster than the case and the other side gearis rotating slower than the case. In Figure 16-14, when thevehicle makes a turn, the action of the differential allows

the outer wheel to turn at 110% of case speed, while theinner wheel turns at 90% of differential case speed. Thesepercentages will vary with the radius of the turn.

Locking differentialThe standard differential works well in most situa-

tions. However, on very slippery surfaces, such as icy ormuddy roads, lack of traction can cause the rear wheels toslip. This is because the standard differential will drive thewheel with the least traction.

If one drive wheel is on dry pavement and the otheris on ice or mud, the ring gear and differential case willdrive the spider gears. However, the spider gears will notdrive both side gears. When the spider gears are driven bythe differential case, they will walk around the side gearrelated to the wheel on dry pavement. As a result, thespider gears drive the slipping wheel, and the vehicle willnot move. The standard differential sends almost all enginepower to the slipping wheel.

To overcome this problem, locking differentials areused. Locking differentials overcome traction problems bysending some power to both wheels, while allowing thevehicle to make normal turns. There are several differenttypes of locking differentials, including limited-slip, ratchet,and Torsen® differentials.

The two most common types of limited-slipdifferential are the clutch-plate differential and the conedifferential. The clutch-plate differential uses several fric-tion discs that look like small manual clutch discs. Thecone differential uses a cone-shaped clutch that engages amatching cone-shaped receptacle. Limited-slip differen-tials have various brand names, including PositiveTraction, Sure-Grip, Anti-Spin, Traction-Lok, and TXT.Many technicians refer to limited-slip differentials asPositraction differentials, although this is actually aGeneral Motors brand name dating back to the 1950s.

Due to their complexity and higher cost, limited-slipdifferentials are used only on high performance versions ofrear-wheel drive automobiles. Limited-slip differentials arecommonly found on modern trucks and SUVs. Many SUVsand some trucks have limited-slip differentials on the frontand rear axles. Some companies make aftermarket limited-slip differentials to replace original equipment designs orto convert standard differentials to limited slip units.

An example of a common clutch-plate differential isshown in Figure 16-15. The most obvious differencebetween this limited-slip differential and a standard differ-ential is the clutch packs placed between the side gearsand the differential case.

The clutch friction discs are made of steel coveredwith a friction material. The clutch plates are made ofsteel. The discs and plates are alternately splined to theside gear and dogged (meaning tabs fit into grooves) to thedifferential case, Figure 16-16. Grooves in the discs orplates are for better grabbing power.

Figure 16-17 shows the moving parts of a clutch-platedifferential. The spider gears, side gears, and other partsare very similar to those used in a standard differential. The


Drive axleDrive axle

Ring gear

Side gears

Case

Spider gears

Figure 16-10. The basic components of a differential caseassembly. The ring gear is bolted to the case, and the spidergears and side gears are mounted inside. On most differentialassemblies, side bearings are pressed onto the case. Alldifferentials contain the same general parts.


12

34

5

6

7

8

9

17

16

20

19

2215

142613

1824

2325

21

12

11

10

1. Drive coupling 2. Thrust washer 3. Lock nut 4. Oil seal 5. Drive pinion gear 6. Front pinion bearing 7. Preload spacer

8. Rear pinion bearing 9. Pinion depth shim 10. Differential carrier 11. Ring gear 12. Differential case 13. Ring gear bolt 14. Pinion shaft

15. Lock screw 16. Pinion gear 17. Thrust washer 18. Side gear 19. Side bearing 20. Shim/spacer

21. Drive axle 22. Drive axle C-lock 23. Bearing cup bolt 24. Bearing cup 25. Differential cover gasket 26. Inspection cover

Figure 16-11. A section view of a typical differential contained in rear axle assembly. The differential case is installed in the rear axlehousing. The ring gear, which is attached to the differential case, meshes with the drive pinion gear. The relative positions of theparts are similar on all differentials. Note the C-locks on the differential side gears. They retain the drive axles in the housing.(General Motors)

differential case of the limited-slip differential is oftenmade in two parts to allow for clutch pack removal, asshown in Figure 16-18.

The discs and plates are applied by the preloadsprings and by the mechanical pressure of the spider gearson the side gears. Since the spider and side gears are bevelgears, their teeth try to come out of engagement when thedifferential is transmitting engine torque. This creates a


Thrustwasher

Side gear Thrustwasher

Spidergear

Lockpin

Pinionshaft

C-lock

Figure 16-12. This is an exploded view of the differential gears.Note the relationship of the side and spider gears to each other.Also note the thrust washers that separate the gears from thecase and the C-lock that holds the axle shaft in place. The pin-ion shaft is held in place by a pin that passes through both theshaft and differential case. (DaimlerChrysler)

Drivingstraight ahead

Drivingaround corner

Piniongear drives

Side gearsand driveaxles turnsame on

both sides

Spider gearslocked, assembly

rotates assolid unit

Ring geardriven

Side gearand drive

axle

Left driveaxle turning

fasterSpider gearsnow turning

Right driveaxle turning

slowerBA

Figure 16-13. Differential action is shown here. Note the use of four spider gears, rather than the regular two. A—Straight ahead:Differential case gears turn as a unit. Both the drive axles and differential case are turning at the same speed. B—Right turn: Theleft axle is moving faster than the right axle. The left side gear drives the pinion gears. The pinion gears turn and walk around theright side gear. Note that the differential works the same way for a left turn, except the action of the left and right sides is reversed.(Deere & Co.)

Outer wheel110% case speed

Inner wheel90% case speed

100% differentialcase speed

Pinion gears rotateon pinion shaft

Figure 16-14. The speed of the differential case on turns is theaverage of the side gear speeds. (DaimlerChrysler)


Differentialside gear

Preloadspring

Ring gearmounting surfaces

Multiple-discclutch sets

Differentialspider gear

Differentialcase

Figure 16-15. Study the assembled view of the clutch-platedifferential. The clutch packs are sandwiched between the sidegears and differential case. The preload spring applies initialforce to the clutch packs but still allows enough slippage in theclutch pack for normal differential operation. (Ford)

Steel plateswith external tabs

Bellevillespring

Externalsplines

Differentialside gearFriction discs

with internal teeth

Figure 16-16. Exploded view shows the clutch pack of alimited-slip differential. Each clutch pack has the same numberof clutch discs and plates. Note the internal teeth on the frictiondiscs and the external tabs on the steel plates. Grooves in thediscs and plates reduce the chance of slippage.(DaimlerChrysler)

Thrust block

Snap ring

Spider gear

Thrust washer

Pinion shaft

Side gear

Bellevillespring

Retainer clipClutch pack

Ring gear

Case

Figure 16-17. This shows the relative positions of the clutch packs, spider gears, and side gears of the limited-slip differential. Noticethe similarity to the standard differential. (DaimlerChrysler)

pushing action on the side gears, forcing them outwardagainst the differential case. The outward pressure of theside gears presses the friction discs and steel plates togetherbetween the side gears and the case. Whenever the discsand plates are pressed together, the splined and doggedconnections ensure the side gear and differential case arelocked together.

The operation of a clutch-plate differential is shown inFigure 16-19. When the vehicle is moving straight ahead,the clutch-plate differential operates in the same manner asa standard differential, Figure 16-19A. The rear wheels andthe differential case turn at the same speed. The clutchpacks are applied, but they are not needed.

When turning, the vehicle loses traction at one wheel,causing the wheel to slip, Figure 16-19B. Since the wheelis slipping, the spider gears do not press tightly on the sidegear of the slipping wheel. The side gear also does notpress toward the case, and the clutch pack of the slippingwheel is not pressed tightly together.

Since there is a normal tendency for the side gears tomove away from the spider gears under load, the otherside gear moves outward and away from the spider gears.The side gear is under load because its related wheel hastraction. The pressure on this side gear causes the relatedclutch pack to be pressed tightly together. The side gear islocked to the case by the clutch pack, and power is deliv-ered to the wheel with traction.

The clutch pack is designed to slip when some presettorque value is reached. When the vehicle is making a turn,a high torque, caused by the outer wheel rotating faster thanthe case, causes the clutch pack to slip. This allows the dif-ferential to operate in the same manner as a standard differ-ential when making turns. The discs and plates slide againsteach other—discs turning with side gears, plates turningwith case—allowing different rotating speeds between caseand side gears and, therefore, between rear wheels.

Figure 16-20 shows a cone differential, which isanother version of the limited-slip differential. In place ofclutch packs, friction-lined cones are used. The operationis similar to that of the clutch-plate differential. Preloadspring and side gear pressures force the cone into a disheddepression in the differential case. Friction tries to lock thecone and, therefore, the side gear to the case, sending


Drive axleinstalls here

Ring gearmount Differential

case Differentialcomponents

Drive axleinstalls here

Sidebearing

Parting line

Sidebearing

Figure 16-18. The differential case of a limited-slip differentialis often made in two parts. Note the parting line on the case ofthis limited-slip differential. (DaimlerChrysler)

Differentialcase

turning

Pinion geardrives

ring gear

Power infrom drive

shaft assembly

Spider and sidegears rotating with

case as a unit

Equalrotationof bothaxles

Clutch packsinoperative

Axles splinedto side gears

Power infrom drive

shaft assembly

Case drivesclutch pack

Large torqueoutput to

drive wheel

Clutches splinedto axle gears

Spider gearsrotating

Small torque

output todrive wheel

Friction in clutchpacks transferspower from case

to side gears

A

B

Figure 16-19. Study the action of the limited-slip differential.A—Traction on both wheels. The differential parts are lockedtogether and rotate as a unit. The clutch packs are not operating.B—One wheel is slipping. Pressure on the side gear of thewheel with traction causes the discs and plates of the relatedclutch pack to grab, sending most of the engine power to thatwheel.

power to the wheel with the most traction. Figure 16-21 isan exploded view of the cone differential.

Note that both clutch-plate and cone differentialsrequire special limited-slip gear oil. Using ordinary gear oilin limited-slip differentials will cause the discs and platesor cones to slip and vibrate during turns.

The ratchet differential, nicknamed a Detroit locker,uses a series of cams and ramps to direct power to thewheel with the most traction. Its operation depends on rel-ative wheel speed, rather than on wheel traction. Theratchet differential transfers power through a set of teeththat can be engaged and disengaged. This kind of engag-ing teeth system is sometimes called a dog clutch. Theseries of cams and ramps disengage the teeth of the dog

clutch on the side of the wheel with the least traction. Anexample of the ratchet differential is shown in Figure 16-22.

For straight-ahead driving, both sets of teeth areengaged, and the differential case and wheels turn at thesame speed, Figure 16-22A. During turns or when onewheel loses traction, the speed difference between thewheels causes the internal cam and ramp to disengage theteeth on the side of the faster moving wheel, Figures 16-22Band 16-22C. All power is then sent through the other wheel.

Since the faster moving wheel is always the one thatis slipping, power always goes to the wheel with traction.On turns, the loss of power to the outer wheel is notnoticeable. This design is durable and does not requirespecial gear oil, but it is often rough and noisy in opera-tion. It is usually used in off-road and racing vehicles.

The Torsen differential is a locking differential usingcomplex worm gearsets. The gearsets include worms (drivegears) and worm wheels (driven gears). The Torsen differ-ential has been available since the 1960s as a high-performance replacement unit for standard differentials. Itis now being offered as original equipment on someEuropean cars. The basic mechanical principle of thisdifferential is that while the worm can drive the wormwheel, the worm wheel cannot drive the worm.

As shown in Figure 16-23, the Torsen differential hastwo central worms. For purposes of clarity, these will bereferred to as axle gears. One axle gear is attached to eachaxle shaft. Worm wheels ride on and are driven by the axlegears. The worm wheels are held in place by the differen-tial case. Spur gears machined on the ends of the wormwheels mesh and form the only connection between thetwo axle shafts. Engine power drives the differential case,and the worm wheels, held by the case, turn with it. Theworm wheels cannot turn the axle gears, so they lockthemselves to the gears. In this way, power is transmitted;the axle gears and axles are locked to the case, and theyrotate with it.


Differential case

Side gears

Cone clutch

Lubricationgrooves

Lubricationpocket

Coilspring

Pinions

Figure 16-20. Study the construction of the cone differential.The operation of this limited-slip differential is similar to that ofthe clutch-plate differential. Pressure on the side gear of thewheel with traction causes the cone to be pressed into thedished area of the differential case, locking the case to the driveaxle on that side. (DaimlerChrysler)

CaseClutch cone/

side gear

Spring

Spider gear

Pinion thrust washer

Spring block

Clutch cone/side gear Case

PinionshaftSpring

block

Figure 16-21. Exploded view of the cone differential shows the relationship of parts. Grooves in the cones help to solidly engagethe case. (DaimlerChrysler)

During straight-ahead operation, the differentialassembly operates like a standard differential; all internalgears turn as a unit. When the vehicle is making a turn, orwhen one drive wheel is slipping, the relative speed of thedrive wheels and, therefore, of the axles, changes. This

speed change is transmitted from the faster axle to theslower one by the action of the meshing spur gears.

The axle gear on the faster axle can drive the respec-tive worm wheels. This driving force is transferred from thespur gears on the faster turning worm wheels to the spurgears on the slower turning worm wheels. Engine power istransferred from the faster to the slower worm wheels bythe interaction of the gears. The worm wheel on the slowerside still cannot drive the slower axle gear, but it can trans-fer the increased power from the faster wheel as pressure.This pressure increases the amount of power sent to theslower axle gear and axle. It does not turn the axle gear,but it does allow it to turn with more force.

Hydraulic Locking DifferentialsSome late model SUVs have locking differentials that

are operated by hydraulic pressure. It may be called aHydra-Lock, Vari-lock, or Georotor system. A hydrauliclocking differential consists of a pump with internal andexternal gears, a ring-shaped pressure diaphragm, and aclutch pack that resembles the clutch pack used in a con-ventional locking differential, Figure 16-24A. The gear oilthat operates the hydraulic system comes from the rear axleassembly sump. Special oil is not needed. The same oil isused for rear axle lubrication, and the hydraulic system doesnot have to be sealed from the other rear axle components.

The pump resembles a rotor-type engine oil pump,with a six-point external gear that turns inside of an inter-nal gear with seven cavities. The spaces between the pumpinternal and external gears are filled with gear oil at alltimes. When the gears move in relation to each other,spaces on the intake side of the pump open and draw ingear oil. The fluid is carried around to the output side ofthe pump, where the spaces begin to close. Closing the


Both driven clutches and center drivemember travel at same speed.

Driven clutch elevated by cams andtravels at faster speed.

Driven clutch elevated by cams andtravels at faster speed.

Driven clutch and center drive memberare locked and rotate at same speed.

Driven clutch and center drive memberare locked and rotate at same speed.

R/H sidegear

L/H sidegear

R/H sidegear

L/H sidegear R/H side

gearL/H side

gear

A B C

Figure 16-22. The ratchet differential uses matching sets of teeth on each side of the differential case. Teeth are engaged anddisengaged to transfer power. A—Differential is straight-ahead operation. Teeth are engaged on both sides of the case, and poweris transferred equally to each wheel. B—When the vehicle makes a left turn, the greater speed of the right wheel causes the internalcam on the right side of the case to take the right-side teeth out of engagement. All power goes through the left axle and wheel.C—When the vehicle makes a right turn, the greater speed of the left wheel causes the left-side cam to take the left-side teeth outof engagement. All power goes through the right axle and wheel. (Ford)

Ringgear

Axle shaft

Axleshaft Differential

case

Spurgears

Worm(axle gear)

Worm wheels

Figure 16-23. The Torsen differential uses a unique arrange-ment of gears to transfer power. This differential has beenavailable as a high-performance aftermarket replacement forabout 25 years. It is now being offered as original equipment onsome European vehicles. The operation of this differential iscomplex. (Torsen)

spaces produces pressure that can be used to operate theother components of the differential assembly. Figure 16-24Bshows the operation of a rotor-type pump. Check valvesensure that pressure is always produced, no matter whatthe direction of pump rotation.

The internal gear is attached to one of the side axles.The external gear is attached to the other side axle. Whenboth wheels have equal traction, both side axles turn at thesame speed. Therefore, the internal and external pumpgears do not move in relation to each other, and no pres-sure is developed. When the vehicle loses traction to onewheel, one of the side axles begins turning at a faster ratethan the other. The difference in axle speeds causes theinternal and external pump gears to move in relation to

each other, producing hydraulic pressure. This pressure isdelivered to the ring diaphragm, which expands againstthe clutch pack. With the clutch pack applied, the sideaxles lock together and turn as a unit. When the wheelsbegin turning at the same speeds, the internal and externalgears do not move in relation to each other, and no pres-sure is produced. With no pump pressure produced, thering diaphragm depressurizes and releases the clutches. Ifone wheel again begins to slip, the pump starts operatingagain, and the system reapplies the clutches.

When the vehicle makes a turn, the pump gears moveslightly in relation to each other. They do not, however, pro-duce enough pressure to apply the clutches. Therefore, thedifferential does not attempt to lock up during normal turns.

Some locking differentials are operated by an electricmotor attached to the axle assembly. Note the additionalparts installed on a standard rear axle, Figure 16-25. The shiftfork shaft and shift fork are operated by the motor and movea hub sleeve. The hub sleeve has splines that can engagematching splines on the differential carrier and side gear.During normal non-locking operation, the shift fork shaft andshift fork are positioned to keep the hub sleeve disengaged.The hub sleeve has no effect on differential operation.

To lock the differential, the motor moves the shift forkshaft and shift fork to engage the hub sleeve splines with thesplines on the differential carrier and side gear. The splines lockthe hub sleeve, differential carrier, and side gear into a singleunit. Locking the carrier and side gear together prevents theother differential gears from turning. The differential assemblyturns as a unit, delivering equal power to each drive wheel.

Rear Axle Housing: Solid-AxleRear Suspension

The rear axle housing contains and supports otherparts of the rear axle assembly. It also forms a reservoir forthe rear end lubricant. The housing accommodates sus-pension system attachment. Most rear axle housings alsosupport the stationary parts of the rear brake assemblies.


Housing

Outerrotor

Inlet Outlet

Highpressure

area

Inner rotor

Close fit sealsinlet and outlet

sides

Lowpressure

area

B

Figure 16-24. A—A hydraulic locking differential, consisting of apump with internal and external gears, a ring-shaped pressurediaphragm, and a clutch pack. B—The arrangement of theinternal and external rotor resembles a rotor type engine oilpump. The close fit of the inner and outer rotors forms a seal atthe point where the teeth almost touch in the pumping chamber.(Daimler Chrysler)

A

Motor

Figure 16-25. Rear locking differential. (Toyota)

The rear axle housing associated with solid-axle rearsuspension consists of a central housing, or differentialcarrier, and axle tubes, which enclose the drive axles andextend to the rear wheels. (Vehicles with independent rearsuspension will not have axle tubes.) Rear axle housingswill have a vent to relieve pressure buildup. They will alsohave oil drain and fill plugs. See Figure 16-26.

Most rear axle housings are made of steel. Steel axletubes are pressed and welded into the housing or are castintegral with the housing. The axle tubes usually have anintegral flange at the outer end. The flange provides amounting surface for the brake backing plate and an axleretainer plate.

Since the rear axle housing is a solid structure, itmoves up and down with the wheels as they move overbumps and holes. To control this movement, the rear axlehousing is attached to the vehicle body through anarrangement of springs, shock absorbers, and control arms,Figure 16-27. These parts align the rear axle assembly tothe vehicle while isolating most of the axle movement.


Rear axlehousing Drive shaft

Fill plug

Drain plug

Figure 16-26. Rear axle assemblies will almost always have fillplugs but not necessarily drain plugs. On a differential without adrain plug, the inspection cover or carrier must usually beremoved to drain the oil. Oil can sometimes be drained byremoving the lowest inspection cover-attaching bolt.(DaimlerChrysler)

Driveshaft

Differentialcarrier

Brake line

Rear axlehousing

Vent hoseU-bolt

assembly

Brake assembly

Axle flange

Brake drum

Suspensionsystem leaf spring

Shockabsorbers

A

Figure 16-27. Two methods of suspending the rear axle assembly of a vehicle with a solid-axle rear suspension are shown. Bothmethods involve the use of conventional shock absorbers. A—Leaf springs support and align the rear axle assembly. This methodsimplifies the assembly, but makes the removal of the rear end difficult.

(continued)

Leaf springs support the axle and hold it in alignment,eliminating the need for control arms, Figure 16-27A.When coil springs are used, separate control arms must beused to maintain rear axle alignment. See Figure 16-27B.

Two kinds of rear axle housings are used on vehicleswithout independent rear suspensions—removable carrierand integral carrier. Both types will be discussed in thissection. (Rear axle housings used with independent rearsuspension will be discussed in the section that follows.)

Removable Carrier

The removable carrier has a separate housing for thedifferential assembly, Figure 16-28. It can be unbolted andremoved from the rest of the rear axle housing after thedrive axles are removed. All of the internal differentialparts, then, will be removed with it. Differential assemblieshoused in this kind of carrier are, in general, easier toservice, since repairs can be done on the bench instead ofon the vehicle.

The carrier mounting flange is where the carrierattaches to the rest of the rear axle housing. Usually,threaded studs are installed in the housing. The studs passthrough holes in the mounting flange when the carrier isinstalled. The carrier is then tightened in place by installing

and tightening nuts over the threaded studs. This attachingmethod makes it easier to align and reinstall the carrier. Agasket is always used between the carrier and axle housing.

The differential pinion bearings are installed in thecarrier in the pinion bearing bores. When tapered rollerbearings are used, the bearing cups are tightly pressed intothe bores. Some removable carriers have an extra supportbearing at the end of the pinion gear. This bearing is calleda pinion pilot bearing.

Figure 16-29 shows the attaching points for the differ-ential side bearings, also called case bearings. The sidebearings are held in place by bolted, U-shaped caps. Most


Control arm

Shock absorber Suspension systemcoil spring

Rear axlehousing

Sway bar

Shims

Oil seal

O-ring

Locknut

Lock washer

Washer

Outer race

Inner race

Bearinghousing

Oil seal

Axle flange

Brake drum

Brake assembly

Axle, orwheel bearing

B

Figure 16-27. (continued). B—Coil springs require the use of control arms and sway bars to maintain alignment. This method makesfor easier rear end removal. (DaimlerChrysler)

Axle tube

Ring gear

Drivepinion gear Removable

carrier

Figure 16-28. The removable carrier type of rear axle housingis a two-piece assembly. The carrier contains differential parts.It can be unbolted and, after the drive axles are removed,serviced on a bench.

differential side bearing mounts have a provision foradjusting the side bearing preload. This adjustment isusually made with a threaded end cap, or adjusting nut.The end cap is tightened against the bearing cup until theproper preload is attained.

Drain and fill plugs may be mounted on the differen-tial carrier or on the rear axle housing, depending on theparticular manufacturer. The ribs on the front of the carrierstrengthen it without adding a great deal of weight to theassembly.

Integral CarrierThe integral carrier, as the name implies, is an inte-

gral part of the rear axle housing. See Figure 16-30. Thistype of rear axle housing has a sheet metal or cast metalinspection cover, sometimes called the differential cover.The inspection cover can be removed to service the rearend components. Service operations must be performedunder the vehicle, since the carrier cannot be separatedfrom the rest of the rear axle housing.

Figure 16-31 shows a typical integral carrier. Noticethat almost all the rear end components are installed inside

the rear axle housing. Most of these can be removedthrough the opening that is kept closed off by the inspec-tion cover. The cover is sealed with a gasket of some sort.

The pinion front and rear bearing cups are pressedinto the carrier portion of the rear axle housing. Integralcarriers do not normally have a pinion pilot bearing.

Differential side bearings are installed in the integralcarrier in the same manner as on a removable carrier. Theside bearing preload adjustment is sometimes made withshims. These shims are placed between the bearing cupand the rear axle housing. In other instances, the preloadadjustment is made with a threaded end cap, as on theremovable carrier.

Rear Axle Housing: IndependentRear Suspension

On vehicles having independent rear suspensions, amodified rear axle housing is used. Figure 16-32 showssuch a housing. Notice that the housing has no axle tubes.The drive axles resemble drive shaft assemblies to somedegree, complete with conventional or constant-velocityuniversal joints. This design allows each wheel to reactindependently to the road surface, improving ride qualityand handling.

The housing has oil seals to prevent oil loss where theaxles enter the housing. The internal construction of thehousing is identical to the previously discussed carriers. Toreduce vibration and strengthen the drive train, a torquetube is sometimes used to attach the front of the housing toone of the vehicle crossmembers. (Torque tubes wereexplained in Chapter 12.)

Rear Drive Axles

The rear drive axles transfer power from the differen-tial assembly to the rear wheels. There are two major kindsof drive axle designs. One is the solid drive axle, shown inFigure 16-33; the other is the independently suspendeddrive axle, shown in Figure 16-34.

Solid Drive AxleA solid drive axle, or live axle, is a hardened-steel

shaft. See Figure 16-35. Each rear axle assembly in solid-axle rear suspension systems has two. External splines onthe inboard (inner) end of each axle mate with internalsplines on the differential side gear to which it is connected.An axle flange at the outboard (outer) end of each axle actsas a wheel hub. It provides the mounting surface for thebrake drum or rotor and the wheel. The brake assembly andwheel are installed directly on the flange wheel studs.

Each shaft is supported on the outboard end by anaxle bearing, also called a wheel bearing. The axle


Pinion bearing Carrier

Side bearing

Side bearing boreCarriermounting flange

Bearing bore

Figure 16-29. The mounting flange of a removable carrier isdesigned to seat against the axle portion of the rear axlehousing. The carrier is attached with studs and nuts. Thegasket is always installed between the carrier and the axlehousing. (Subaru)

Axle tubeDrive pinion

gear

Rear axlehousing

Ringgear

Gasket surface

Inspection cover

Integral carrier

Figure 16-30. The rear axle housing with an integral carrier isessentially a one-piece unit. All moving parts are inside thehousing. The differential parts are reached for service byremoving the inspection cover at the rear. This type of axle isusually serviced under the vehicle.

bearing can be installed on the shaft or in the axle tube.Axle bearings that are installed on the shaft are

usually packed with grease. An axle seal is pressed into thehousing behind, or on the inboard side of, the bearing. Thelip of the seal seats against a machined area of the shaft.This seal keeps rear end lubricant from reaching the bear-ing. An outer seal prevents water and dirt from leakingthrough the outer ends of the rear axle housing and enter-ing the bearing.

Axle bearings that are installed in the housing arelubricated by rear end lubricant (gear oil). When the vehi-cle makes a turn, lubricant is thrown outward from the car-rier, reaching the axle bearing. An axle seal is installed infront of, or on the outboard side of, the bearing to keep

lubricant from leaking out from the outer ends of the rearaxle housing. The shaft is held in place by a clip asexplained in the next section.

An axle bearing installed on the shaft is held in place byan axle collar. The axle collar is tightly pressed on the shaft.In addition, some will have a spacer to keep the bearing atthe proper distance from the end of the axle. The axle retainerplate holds the axle and axle bearing to the axle tube.

Semi-floating axlesSolid drive axles can be semi-floating or full-floating.

Most automobiles and light trucks have semi-floatingaxles. In the semi-floating axle, the weight of the vehicle


Axle flange

Seal

Axle bearing

Screw

Collapsiblespacer

Cup

Pinionyoke Nut

Washer

Seal

Cone and rollers

Axle flange

Stud

SealAxlebearing

Axle tube

Washer

Screw

Lock

Cap

Adjuster

Cup

Bolt

Cone androllers

Shaft

Case

BoltRing and pinion

drive gears

Shim

Cup

Cone and rollers

Adjuster

WasherWasher Cup

CapScrew

Side gear

Pinion

Washer

Lock

Lock

Side gearWasher

Plug

ScrewInspection cover

Figure 16-31. This is an exploded view of an integral carrier rear axle assembly. Notice that most of the moving parts fit inside therear axle housing. The inspection cover often contains a fill plug. (DaimlerChrysler)


Drive shaft

Torque tube

Differentialcarrier

Independentrear suspension

Drive axle

CV-joint

Crossmember

Figure 16-32. The rear axle housing used on vehicles with independent rear suspension has no axle tubes.The carrier has oil seals wherethe drive axles enter. A torque tube is often used at the front of the housing to increase rigidity and reduce vibration. (DaimlerChrysler)

Lugs

Axleflange

Solid driveaxle

Axle tube

Drive piniongear

Differentialassembly

Splinedconnections

Inspectioncover

Ring gear

Spider andside gearsAxle

bearing

Figure 16-33. The axle shaft used on a solid drive axle, or a live axle, is a single piece of steel that is supported on both ends. Theouter support is provided by an axle bearing, and an inner support is provided by the differential side bearings. Note that thedifferential has been rotated 90° for the purpose of illustration. (Fiat)

passes through the axle bearing to the drive axle and on tothe wheel and tire. Figure 16-36 shows three versions ofthe semi-floating axle.

Figure 16-36A shows a semi-floating axle using a ballbearing. This is a pregreased bearing. There is an axle sealbehind the bearing. The axle collar is pressed onto the axleshaft. The bearing and axle are held in the housing by anaxle retainer plate, mounted on the outer end of the rearaxle housing. The retainer plate and bearing control end-play during turns.

Figure 16-36B shows a roller bearing version of thesemi-floating axle. This bearing is lubricated by rear endlubricant. The axle seal is installed in front of the bearing.When this kind of bearing is used, the axle is held in thehousing by a clip on the inboard end of the shaft, at the dif-ferential assembly. This kind of axle is sometimes called aC-lock axle, because of the shape of the locking clip.Endplay on turns is controlled by the fit of the axle shaftbetween the C-lock and the other parts of the differentialassembly.

Figure 16-36C shows a semi-floating axle using atapered roller bearing. This type of axle is usually found onolder vehicles. When this type of bearing is used, there isusually some provision for adjusting the bearing preload tocontrol endplay. This is generally done by using axle shimsor by turning an adjusting nut. Tapered roller bearings maybe packed with grease or lubricated from the rear axle


Rubber seat

Coil springDifferential

mounting insulator

Differentialassembly

Driveaxle

Insulator

Bumper rubber

Dust cover

Shock absorber

Disc rotor

Suspension arm

Suspensionmember stay

Stabilizer

Figure 16-34. Axle shafts used on vehicles having independent rear suspensions somewhat resemble drive shafts. A flexible joint,such as a CV joint, is used on each end of each shaft.

Shaftinnerseal

Axleretainer plate

Axle shaft

Axle flange(wheel hub)

Sealretainer

Shaftouter seal

Axlecollar

Axlebearing

Figure 16-35. Drive axle and related components are shownhere. The external splines on the inboard end of the axle matewith the matching internal splines in the differential side gear.The axle flange is a mounting surface for the brake drum orrotor and wheel. The bearing is kept in place by the axle collar.The axle retainer plate keeps the axle and bearing retained inthe axle tube. (DaimlerChrysler)

housing, depending on the particular manufacturer’s design.In Figure 16-36C, notice the use of the tapered axle.

This is one of two methods used to secure a wheel hub toits axle. The tapered end wedges into a tapered hole in thewheel hub, and the key keeps the axle from rotating in thehub. The other method, mentioned earlier, has the wheelhub (axle flange, in this case) solidly mounted to the axle.

The design of the semi-floating axle causes weightloads to be placed on the axle. These loads will shift as theaxle rotates, placing flexing stresses on the shaft. On auto-mobiles and light trucks, the loading is not serious and theaxles will usually last the life of the vehicle.

Full-floating axlesIf the rear end will be subjected to heavy loads, such

as the rear end of a large truck might be, a full-floating axleis used. Figure 16-37 shows an example of a full-floatingaxle. With this design, the axle drives the wheel but doesnot carry any of the vehicle weight. The weight passesthrough the bearings on the wheel hub. The wheel hubabsorbs the stresses. This design reduces the stresses onthe shaft, prolonging its life. Full-floating axles are notused on light duty vehicles because of their extra cost andcomplexity.

Independently Suspended Drive AxleIndependently suspended drive axles, used on

vehicles with independent rear suspension, resembleminiature drive shaft assemblies. The axle consists of acentral shaft with flexible joints and stub axles on eachend. The flexible joints—either cross and roller U-joints or


Axleflange

Axle retainerplate

Brake backing plate

Seal Axlecollar

Axlesupports

and driveswheel

Axle sealReal axlehousing

Axle bearing

Retainer-to-housing bolt

Wheellug stud

Axlebearing

Rear axle housingBrake backing

plate

Drive axle

Gear oil

Axlehousing

seal

Axle flange

Rear axle housing

Brake backing plate

Ring sealKeyWasher

Nut

Outerretainer

plateTapered axle

supports wheelhub and

drives wheel

Axle seal

Axle bearingBolt

Washer

Endplay adjustingaxle shims

C—Tapered roller bearing semi-floating axle. The bearing preload is adjusted by shims or an adjusting nut. The axle is retained in same manner as ball bearing, except without the axle collar. The shoulder on the axle keeps the axle from sliding past the bearing.

A—Ball bearing semi-floating axle. The ball bearing is retained on shaft by a pressed on axle collar. The bearing and axle are held in the housing by a bolted retainer plate.

B—Roller bearing semi-floating axle. The major difference between this design and that of ball bearing is the shaft locking method. This axle is retained by a C-lock at the inside of the shaft. The C-lock attaches axle to the differential. The bearing plays no part in keeping the shaft in place.

Figure 16-36. The semi-floating axle is the most common shaftand bearing design used on cars and light trucks. The bearingpasses the vehicle weight through the axle shaft and out to thewheel. The axle drives and supports the vehicle.(Fiat, General Motors, Deere & Co.)

Axlebearing

Drive wheelHub, not axle, supports

weight of car

Axle bearing

Driveaxle

Axlehousing

Wheel hub supportedby bearings onaxle housing

Wheel hub

Sleeve nutsretain bearing

Figure 16-37. The full-floating axle is used on trucks and othervehicles that carry heavy loads. Bearings on the hub transmitthe vehicle weight from the rear axle housing to the wheel huband the wheel without the loading axle. The only job of the axleis to propel the vehicle. (Deere & Co.)

Rzeppa-type CV joints—allow each wheel to move inde-pendently of the vehicle body and of each other.

A typical independently suspended drive axlearrangement is shown in Figure 16-38. Although they lookdifferent, these axles transfer power in much the samemanner as solid drive axles.

Figure 16-39 is an example of how an independentlysuspended drive axle and wheel hub are assembled. Thehub is firmly attached to the suspension control arm. Theinner portion of the hub rotates inside of a bearing and actsas a mounting flange for the wheel and brake assembly.The stub axle is splined to the hub and drives it. Theuniversal joint allows free movement of the suspensioncontrol arm. Some splined axles can slide to compensatefor changes in axle length when the rear suspension movesup and down.

Summary

All rear axle assemblies have the same basic designand operate by the same principles. Rear end variationsdepend on whether the vehicle has a solid-axle or inde-pendent rear suspension, a removable or integral carrier,semi-floating or full-floating axles, and a standard or limited-slip differential.

The major parts of the rear axle assembly are the dif-ferential assembly, rear axle housing, drive axles, bearings,and seals. Engine power enters the drive pinion gearthrough the differential pinion yoke and drive shaft assem-bly. The drive pinion gear turns the ring gear. The

interaction of the ring and pinion assembly turns the powerat a 90° angle and reduces its speed. The ring gear is bolt-ed to the differential case. Power flows from the ring gearinto the differential case, which transfers the power to thespider gears. The spider gears transfer the power to sidegears, which then transfer the power to the drive axles andrear wheels.

The differential assembly has three purposes. It redi-rects the drive shaft rotation in a 90° angle, reduces rotat-ing speed to increase power, and allows the vehicle tomake turns without wheel hop or axle breakage.

The relative positions of the ring and drive piniongears must be set exactly, or the gears will be noisy andwear out prematurely. The position of the ring and drivepinion gears in the case and in relation to each other mustbe carefully adjusted.

The differential case assembly allows the vehicle to maketurns without wheel hop. It has an arrangement of gears thatallows the rear wheels to turn at different speeds. There are twokinds of differential case assemblies, standard and locking.

The standard differential is composed of meshing spi-der and side gears, enclosed in a differential case. The ringgear is bolted to the case. Power flow is through the case,into the spider gears, and on to the side gears. The sidegears are splined to the drive axles. They transfer power tothe drive axles and rear wheels.

When driving on slippery surfaces, the rear wheels ofa vehicle with a standard differential will often slip. This isbecause the differential will always drive the wheel withthe least traction. To overcome this problem, various kindsof locking differentials are used. They increase traction bysending power to the wheel with the most traction.


Wheelbearings

Rear drive axle(central shaft)

Differentialhas been

rotated (top view)

Stub axle

CV joint

DifferentialStubaxleCV joint

Independentrear suspension

CV joint

Figure 16-38. The drive axle of a vehicle with an independent rear suspension consists of three shafts and two U-joints. The centralshaft is connected through the U-joints to a short shaft, or stub axle, on either side. Stub axles are splined to the wheel hub andside gears. Note that the differential has been rotated 90° for the purpose of illustration.

The most common locking differential is the limited-slip differential. One type uses clutch packs placedbetween the side gears and the differential case. Frictiondiscs are splined to the side gears; steel plates are doggedto the case. The clutch packs are pressed together by thepressure of the spider gears on the side gears.

When the vehicle is moving straight ahead, the limited-slip differential operates like a standard differential. Therear axle parts turn at the same speed, and the clutch packsare not used. When a wheel starts slipping, the differencein pressure on the side gears causes the clutches to apply.The difference in traction between the inner and outerwheels is not a factor during normal turns, and the frictiondiscs and steel plates slip over each other.

Another version of the limited-slip differential usescones instead of clutch packs. Operation is similar to theclutch-plate differential.

The ratchet differential has a series of internal cams andramps that direct power to the wheel with the most traction.Its operation depends on relative wheel speeds, rather thanwheel traction. The ratchet differential transfers powerthrough a set of teeth, which can be engaged and disengaged.

The Torsen differential uses an arrangement of worms(drive gears) and worm wheels (driven gears) to transferpower. On turns or when one wheel is slipping, the axlegear and worm wheel arrangement transfers power fromthe faster wheel to the slower wheel.

The rear axle housing encloses and supports the otherparts of the rear axle assembly and forms a reservoir for therear end lubricant. The rear brake assemblies are usuallyattached to the rear axle housing. The rear axle housing isattached to the vehicle body by the suspension system.

Two kinds of rear axle housings are used on vehicleswithout independent rear suspensions. The removable carriertype has all of its moving parts, except the axles, in a carrier


Brake disc rear

Wheel bearing

Stub axle

Axle oil seal

Rear wheel hub

Disc shroud

Brakecarrier plate

Spacertube

Rollerbearing

Oil seal

Rear drive axle(central shaft)

Shock absorber

Cardan U-joint

Dustcap

Gasket ring

Control arm left

Figure 16-39. This shows how a stub axle and universal joint of an independently suspended drive axle are installed to a hub andwheel of a vehicle with an independent rear suspension. (Porsche)

that can be unbolted from the rear axle housing. The integralcarrier type is a one-piece unit. It is serviced by removing asheet metal inspection cover, located at the rear of the housing.

A modified rear axle housing is used on vehicleshaving independent rear suspension. The internal construc-tion of the housing is identical to those used on live axles.(A version of this housing is used on some front-wheel drivevehicles that have the engine mounted longitudinally.)

The rear drive axles transfer power from the side gearsto the rear wheels. Drive axles can be solid or independ-ently suspended. Solid axles are splined with, and supportedby, the side gears at the inboard end. The outboard end issupported by axle bearings. The axle bearing can beinstalled on the shaft or in the housing. Bearings that areinstalled on the shaft are usually packed with grease.Bearings that are installed in the housing are lubricated byrear end lubricant. Seals are used to keep lubricant fromleaking out of the rear axle housing.

Solid axles can be semi-floating or full-floating. In thesemi-floating axle, the weight of the vehicle goes throughthe axle bearing to the shaft and out to the wheel. In thefull-floating axle, the axle drives the wheel but does notcarry any of the vehicle weight. Most passenger cars havesemi-floating axles.

Independently suspended drive axles resemble driveshaft assemblies. They consist of a central shaft with flexi-ble joints and stub axles on each end. The flexible jointscan be conventional U-joints or CV joints. They alloweach wheel to move independently of the vehicle bodyand of each other.

Review Questions—Chapter 16

Please do not write in this text. Place your answers ona separate sheet of paper.

1. Which of the following items does not belong withthe others?(A) Rear axle assembly.(B) Final drive.(C) Differential.(D) Rear end.

2. What is independent rear suspension?

3. Which rear end components change the direction ofpower flow by 90°?

4. How can rear axle ratio be determined?

5. If the drive pinion gear has 10 teeth and the ring gearhas 35 teeth, what is the rear axle ratio?

6. Describe the construction of a drive pinion gear.

7. Which of the following parts is used to set pinionbearing preload?(A) Jam nut.(B) Crush washer.(C) Lock washer.(D) Castle nut.

8. The convex side of ring gear teeth is the _____ side, andthe concave side of ring gear teeth is the _____ side.

9. The standard differential is composed of meshing_____ and _____ gears enclosed in a differential case.

10. In terms of their construction, what is the majordifference between a standard differential and a limited-slip differential?

11. The Torsen differential is a locking differential thatuses a _____.(A) multiple-disc clutch(B) cone clutch(C) dog clutch(D) worm gearset

12. Explain the function of the rear axle housing.

13. Describe the two major kinds of carriers.

14. In the _____-floating axle, the weight of the vehiclepasses through the axle bearing to the drive axle andon to the wheel and tire.

15. In a(n) _____-floating axle, the wheel does not carryany of the vehicle weight.

ASE-Type Questions—Chapter 16

1. Technician A says that every rear axle assembly has ahousing, a differential assembly, and rear drive axles.Technician B says that every rear axle housing hasaxle tubes. Who is right?(A) A only.(B) B only.(C) Both A and B.(D) Neither A nor B.

2. The most common rear axle assembly failures are_____.(A) axle bearing failures(B) pinion yokes failures(C) cracked spider gears(D) stripped ring and pinion gears

3. Each of the following is a primary function of thedifferential assembly except:(A) multiplying engine power.(B) allowing the vehicle to make turns.(C) supporting and aligning the drive axles.(D) redirecting power flow to the rear wheels.

4. Rear axle ratio can be found by dividing the numberof teeth on the ring gear by the number of teeth onthe _____.(A) side gear(B) spider gear(C) drive pinion gear(D) axle end gear


5. Each of the following is used to set the pinion bearingpreload except:(A) a solid spacer.(B) a crush washer.(C) a collapsible spacer.(D) the rear pinion bearing.

6. The ring gear transfers power directly from the drivepinion gear to the _____.(A) axle flange(B) differential case(C) differential carrier(D) differential pinion yoke

7. A rear-wheel drive vehicle cannot be driven becauseone of its drive wheels is parked on ice. Technician Asays that the ring gear and differential case will drivethe spider gears. Technician B says that the differentialspider gears will walk around the side gear related tothe wheel on dry pavement. Who is right?(A) A only.(B) B only.(C) Both A and B.(D) Neither A nor B.

8. Locking differentials overcome traction problems bysending power to _____.(A) the wheel with traction(B) both wheels(C) the slipping wheel(D) the wheel bearings

9. Each of the following is a locking differential except:(A) Torsen differentials.(B) ratchet differentials.(C) limited-slip differentials.(D) MacPherson differentials.

10. Each of the following functions is served by the rearaxle housing except:(A) determining the depth of the drive pinion gear in

the carrier.(B) forming a reservoir for rear end lubricant.(C) accommodating suspension system attachment.(D) supporting stationary parts of rear brake assemblies.

11. Each of the following types of drive axles is found onrear-wheel drive vehicles except:(A) full-floating axles.(B) Rzeppa axles.(C) semi-floating axles.(D) independently suspended axles.

12. Major differences among rear-wheel drive vehicleswith solid-axle rear suspension include each of thefollowing except:(A) conventional versus constant-velocity U-joints.(B) removable versus integral carrier.(C) semi-floating versus full-floating axles.(D) standard versus limited-slip differential.


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