The Touareg Suspensionand 4XMOTION Systems

Self-Study ProgramCourse Number 89H303

Volkswagen of America, Inc.Service TrainingPrinted in U.S.A.Printed 4/2003Course Number 89H303

2003 Volkswagen of America, Inc.

All rights reserved. All Information contained inthis manual is based on the latest informationavailable at the time of printing and is subject to the copyright and other intellectual propertyrights of Volkswagen of America, Inc., its affiliated companies and its licensors. All rights arereserved to make changes at any time withoutnotice. No part of this document may bereproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recordingor otherwise, nor may these materials be modified or reposted to other sites without the prior expressed written permission of the publisher.

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Always check Technical Bulletins and theVolkswagen Worldwide Repair InformationSystem for information that may supersede anyinformation included in this booklet.

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iTable of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1The Touareg Chassis, The 4-Wheel Concept

Front Axle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Component Overview, Lower Control Arm Connection

Rear Axle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Sub-Frame, Component Overview

Suspension/Damping System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Suspension Struts

Air Suspension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Air Suspension System, Air Suspension Level Adjustment, Air SuspensionShock Damping Regulator, Shock Damping Adjustment Valve, Front Axle AirSpring and Shock Damper, Rear Axle Air Spring and Shock Damper, Air SupplyPump, Accumulators, Tire Inflation Connection, Sensor/Actuator System, LevelChange, Vehicle Jack Mode, System Overview

Brake System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Overview, Brake Equipment, Parking Brake, Anti-Lock Brake System ABS/ESPContinental/Teves MK 25, Electronic Differential Lock (EDL), Hill DeclineAssistant, Off-Road ABS

Steering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Steering System, Steering Column

Wheels and Tires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Tire Pressure Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Tire Pressure Control System, System Overview, Tire Pressure SensorsG222...G225, Tire Inflation Connection

4XMOTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Overview, The Transfer Case, Center Differential Lock, Center DifferentialReduction Stage, Rear Differential Lock, Electronic Drive Train Management,Control Strategy

Special Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Knowledge Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Page

New!

Important/Note!

The Self-Study Program provides you with informationregarding designs and functions.

The Self-Study Program is not a Repair Manual

For maintenance and repair work, always refer to thecurrent technical literature

1Introduction

The chassis of the Touareg sets new stan-dards with its outstanding on and off-roadproperties. The Touareg combines the bestproperties of off-road vehicles andsedans/hatchbacks.

The design of the front and rear axlesensures the noise and comfort level of aluxury sedan, and the wheel location pro-vides the driving precision of a sports car.The suspension system, with optional airsprings and electronically controlled shockabsorbers, provides a very high level of sus-pension comfort both on and off the road.

The Touareg is equipped with the electroni-cally controlled 4XMOTION system.

A transfer case, equipped with off-roadreduction, delivers the engine power to thedrive wheels via limited-slip differentials.

Depending on requirements, up to 100% ofthe drive force can be delivered to one ofthe two axles. The standard 4-wheel EDLdistributes the drive force between thewheels.

The short front and rear body overhangs, aswell as the large ground clearance and ford-ing depth, are other characteristics of theTouareg's off-road capability. Its climbing abil-ity and lateral inclination also enable off-roaduse in extreme terrain.

Introduction

The Touareg Suspension

The suspension in conjunction with4XMOTION delivers exceptional off-roadperformance with its center differentialand reduction stage.

Its independent suspension also helpsensure the highest driving comfort onnormal roads.

Introduction

2

Tire Inflation Connection Under the Right FrontSeat (only on vehicles with air suspension)

Dual Wishbone Front Suspension

Dual Wishbone Rear Suspension with SplitUpper Transverse Link

Front and Rear Anti-Roll Bars

Independent Suspension

Air Suspension with Regulated Damping(Optional on V6 and V8)

3Introduction

Center and Rear Axle Differential Locks

Foot Parking Brake,Duo Servo Drum Brake

Tire Pressure Monitoring(optional at a later date)

Ventilated Disc Brakes(front and rear)

Continental/Teves MK25 ABS System withBraking Assistant and EDL

Hill Incline Assistant,Hill Decline Assistant

The 4XMOTION Concept

The Touareg has the technical prerequisites for excellent off-road capability with either thestandard steel springs or the optional air spring suspension. It has short body overhangs,high ground clearance, a deep fording depth, a steep climbing capability, a steep lateralincline, an excellent ramp and pitching angles. These all enable the Touareg for extremeoff-road use.

Introduction

4

Body Overhangs Front and Rear:

33 - Air Suspension

28 - Steel Suspension

Climbing Capability:

45 - Air Suspension

45 - Steel Suspension

Ground Clearance:

12 in (300 mm) - Air Suspension

8 in (200 mm) - Steel Suspension

5Introduction

Lateral Inclination:

35 - Air Suspension

35 - Steel Suspension

Ramp Angle:

27 - Air Suspension

22 - Steel Suspension

Axle Pitching:

6.7 in (173 mm) - Air Suspension

6.3 in (157 mm) - Steel Suspension

Fording Depth:

23 in (580 mm) - Air Suspension

20 in (500 mm) - Steel Suspension

The Front Axle

Component Overview

The front axle of the Touareg has dual wishbone suspension with a large base (solid steelconstruction).

Front Axle

6

7Front Axle

Lower Control Arm Connection

The lower control arm is connected to thewheel bearing housing from above.

Front Axle

8

Tie Rod Connection

9Rear Axle

Sub-Frame

The sub-frame for the rear axle has a pipe-frame construction.

It supports the following components:

Upper and lower control arms

Stabilizer bar

Tie rod

Rear axle differential

Hydraulic bushings isolate the sub-frame andreduce road noise transfer to the body.

Rear Axle

Component Overview

The rear axle also has dual wishbone suspension. However, the upper control arm is splitinto two components.

Rear Axle

10

11

Rear Axle

Suspension Struts

Either steel spring suspension struts oroptional air spring suspension dampers areused on the Touareg.

Suspension/Damping System

12

Steel Spring Suspension Strut

Ground clearance 9.48 in. (237 mm)

Air Spring Suspension Damper

Ground clearance 6.4 -12 in. (160 -300 mm)

13

Air Suspension

Air Suspension Level Adjustment

The air suspension enables the suspensionto be adjusted for every situation.

The chassis switch (right rotary switch) isused to set the ground clearance from 6.4in. (160mm) to 12 in. (300 mm). Loweringthe vehicle improves the road position andreduces wind resistance. When the vehiclereaches certain speeds, the level is adjustedautomatically.

At 112 mph (180 km/h) or faster,the vehicle is lowered automati-cally again by 0.4 in (10mm).

The height specifications arecountry specific and subject tochange. Please check vwweb-source.com for the latest speci-fications.

Under 3 mph (5 km/h)Loading level

Over 80 mph (125 km/h)High speed I

Under 50 mph (80 km/h)Street level

Under 25 mph (40 km/h)Off-road level

Under 15 mph (25 km/h)Xtra level

Air Suspension

14

Air Suspension Shock Damping Regulator

The Touareg's shock damping regulatorincreases driving comfort in all driving situa-tions.

In the Touareg, the shock absorber dampingis set using the damping regulator switch inthe middle of the chassis control panel onthe center console. This switch controlswhether the shock absorbers are soft, firm,or adjusted automatically depending onsensed terrain.

Shock damping settings:

Auto - middle damper setting(standard)

Sport - hard damper setting

Comfort - soft damper setting

Also located on the center console, the lockbutton limits the maximum speed in off-roadlevel to approximately 45 mph (70 km/h). Thisprevents the vehicle from being lowered inoff-road terrain.

With a sporty driving style, e.g.fast curves, damping is automat-ically set to "Sport" regardless ofthe thumbwheel setting. In the"Sport" damper setting, the vehi-cle is lowered to High Speed 1level even when below 80 mph(125 km/h)

15

Air Suspension

Air Suspension System Overview

The air suspension system has beendesigned with strong components to sup-port the weight of the Touareg.

The Touareg system has: Two wheel acceleration sensors

Two large accumulators with a volumetriccapacity of:

- 4.8L for accumulator 1

- 5.2L for accumulator 2

An air compressor with integrated airdryer

Large volume air spring elements in theair spring suspension dampers

External valves for damper adjustment

Tire inflation connection

Large cross section of the air supply lines (6mm)

Shock Damping Control

The control system for the shock absorberdamping regulator uses wheel accelerationsensors and three body acceleration sensorsto monitor the road condition through vehi-cle movement.

The characteristic curves of the individualshock dampers are adjusted according to thecalculated damping requirement. Here thedampers work as semi-active components inextend and compress mode.

Continuous shock damping control (CDC) isbased on shock dampers that can be adjust-ed electrically. These shock dampers areintegrated into the air spring dampers.

The shock damping force is adjusted accord-ing to a map and by using a proportion valvepositioned on the shock damper. With thisvalve it is possible to adapt the damping forceto the driving situation and the road condi-tions within milliseconds.

The system tries to adjust the shock damp-ing force according to the "sky-hook controlstrategy". The shock damper is adjusted inproportion to the vertical acceleration of thewheels and the vehicle body. Ideally, damp-ing is regulated so that the vehicle body"hangs on a sky-hook" and floats above theroad with almost no disruptive movements.

Air Suspension

16

Large control currents lead to harddamping. Small control currentslead to soft damping. The middlecharacteristic curve results whenthere is no control current.

17

Shock Damping Adjustment Valve

The shock damping force of the CDC two-pipe gas shock absorber can be adjustedover a wide range by an electrically con-trolled valve mounted on the damper.

By changing the current to the solenoid, theoil flow through the CDC valve, as well asthe damping force, can be adjusted to therequirements within a few milliseconds.

Oil flows through the CDC valve in the sameway in both rebound and bump directionsusing the check valve function of the pistonas well as the bottom valve.

The wheel acceleration sensors mounted tothe front axle dampers send signals, which,together with the signals from the bodyacceleration sensors, are used to calculatethe required shock damper setting.

The fast detection and control betweenbump and rebound stages ensure that onlythe damping force required for the drivingsituation is applied.

The shock damping maps are stored in theLevel Control System Control Module J197.

Air Suspension

With certain driving conditions, usually with longitudinal and/ortransverse movements, self-leveling is temporarily disabled andshock damping regulation becomesharsh to maintain vehicle control

Front Axle Air Spring andShock Damper

The air spring shock dampers are designedfor the weight of the Touareg. The featuresof these air spring dampers are:

The large air capacity of the bellows, and

The external CDC valve for shock damp-ing adjustment

Air Suspension

18

19

Rear Axle Air Spring and Shock Damper

Air Suspension

Air Supply Pump

The air supply pump is mounted to a vibra-tion-isolated holder on the front right under-body. A plastic cover with ventilation holesprotects it from dirt.

Air for the compressor is supplied from themotor air filter. The air is drawn via thesilencer/filter, cleaned and then used in thecompressor.

An integrated temperature sensor protectsthe compressor from overheating.

The air supply pump consists of:

The compressor unit with

- electric motor,

- dry run compressor,

- air dryer,

- electromagnetic discharge valve,

- silencer with air filter,

- integrated sensor for compressortemperature (temperature sensor foroverheat protection),

- pneumatic discharge valve withresidual pressure retaining functionand maximum pressure limit

Tire inflation connection and

The solenoid valve block with the controlvalves for each air spring damper andfor the accumulator and an integratedpressure sensor for monitoring.

Air Suspension

20

21

Air Suspension

Air Dryer

The air in the pressure system has to bedehumidified so that condensation does notcause corrosion or freezing. An air dryer isused to dehumidify the air.

The compressed air in the self-levellingcontrol system passes through the silicategranulate and is dried in the process.

This granulate can, depending on thetemperature, absorb more than 20% of itsown weight in moisture. When the dried airis discharged (during lowering), this air flowsback through the granulate on its way outinto the open, and in doing so draws themoisture out of the granulate that wastemporarily stored there.

Due to this regenerative process, the airdryer requires no maintenance.

Air Dryer Configuration

The air dryer configuration has a separateline that can be used to inflate the spare tire.The spare tire inflation connection is locatedin the base of the front passenger seat.

Air Suspension

22

23

Accumulators

The purpose of the accumulators is to guar-antee fast and silent level-regulation up to aspeed of 30 mph (50 km/h). The maximumpressure of the accumulators is 240 psi (16.5bar). If the pressure in the accumulators fallsbelow 160 psi (11 bar), the compressor startsand adjusts the vehicle to the set level. Therear accumulator has a volume of 4.8L andthe front 5.2L.

Tire Inflation Connection

When air is withdrawn from the compressorto inflate the spare tire, a reed contactswitches the solenoid valves of the com-pressor off. Thus, no air can escape from thewhole system (level change).

Sensor/Actuator System

The signals from the vehicle level senders,wheel acceleration senders and the vehicleacceleration sensors are used by the thelevel control system control module to adjustthe vehicle height through the air supplypump and the solenoid distribution block.

Level Change

When the vehicle level is changed, the barindicator in the display unit on the dashpanel insert flashes until the selected level isreached.

Vehicle Jack Mode

Vehicle jack mode should be activated anytime the wheels of the vehicle are to be lift -ed off of the ground, either through changinga tire or raising the vehicle on a hoist. Thismode locks the system and prevents over-extension of the air springs.

Switching On

The vehicle is stationary

Ignition on

Parking brake applied

Press and hold the lock button for morethan 5 seconds

Switching Off

Drive faster than 5 km/h or

Press and hold the lock button for morethan 5 seconds

Air Suspension

If vehicle jack mode is activated,the level that was previously set iskept in memory and an indicatorappears in the instrument panelinsert.

Air Suspension

24

System Overview

25

Air Suspension

Brake System

26

Overview

The Touareg has a new high performancebrake system with ventilated front and reardisc brakes. Other features are ElectronicBrake force Distribution (EBD), a foot parkingbrake which mechanically locks the rearwheels, and the Brake Assistant.

27

Brake System

Brake Equipment

To achieve excellent deceleration values duringbraking, the Touareg is fitted with large frontand rear brakes.

Brake System

28

Front Brakes

The brake discs are ventilated and theBrembo calipers are constructed of aluminum.The Touareg has a brake pad wear indicator forthe front and rear disc brakes so that brakepad wear out can be detected before compo-nent damage.

29

Rear Brakes

The Touareg's rear brakes are high perfor-mance ventilated discs.

The fixed aluminum caliper has four pistons.

A drum-style parking brake is integrated intothe brake disc. The following pages describehow this parking brake functions.

Brake System

Parking Brake

A foot-activated parking brake holds thevehicle securely in place when desired.

The parking brake lever is located in thefootwell in the A-pillar area.

The parking brake is a drum brake with brakeshoes housed inside of the rear brake rotor.These brake shoes press out on the insideof the disc brake rotor, providing the desiredbraking action.

The release handle and control cable forreleasing the parking brake are integratedinto the instrument panel.

Brake System

30

31

Parking Brake Pedal

The parking brake pedal is used to apply andrelease the parking brake. It is a self-adjusting mechanism and needs no mainte-nance.

Applying the Brake

The toothed piece and parking brake pedalare mounted on a pivot bearing and are fixedto each other.

Pressing the parking brake pedal actuatesthe control cable. A ratchet that locks intothe toothed piece holds the brake.

The force of the spring on the catch leverprevents the ratchet from jumping out.

At the same time, the damper is com-pressed. The brake cable is pulled.

Releasing the Brake

When the driver pulls the release lever, thecatch lever lifts the ratchet, which releases thetoothed piece. The release lever spring, nowtensioned, pulls the release lever back into itsnormal position when the driver lets go.

The compressed damper with itsspring/damping action guides the parkingbrake pedal slowly back to its startingposition.

Brake System

The Adjustment Mechanism

An adjustment mechanism is integrated intothe foot parking brake module to ensure thatthe control cable to the rear wheel brakesalways has the optimal length. This adjust-ment mechanism is integrated into the park-ing brake pedal.

Pre-Loaded Mechanism

The spring for control cable adjustment ispre-loaded. A catch lever locks into thetoothed rod inside the spring. The triggerspring presses on the catch lever to preventit from jumping out and thus from triggeringthe adjustment mechanism too soon. Whenthe driver applies and releases the foot park-ing brake, the whole adjustment mechanismmoves up and down.

Brake System

32

33

Self-Adjustment upon Parking Brake Release

When release lever is pulled, the catch leverwill fall quickly to the trigger end stop.

This pushes the catch lever up against theforce of the trigger spring and momentarilyreleases the toothed rod. The pre-loadedspring for control cable adjustment canmove upwards on the toothed rod and adjustthe cable length accordingly.

Brake System

Applying the Brake

Pressing the parking brake pedal pulls thebrake cable, which then actuates theexpander lock lever.

The expander lock pushes the brake shoesapart, pressing them against the inner sideof the brake drum. This holds the vehiclesecurely in place.

Brake System

34

35

Releasing the Brake

When the brake is released, there is nolonger any tension on the brake cable.

The springs pull the brake shoes together sothat they no longer press against the innerside of the brake drum and the expanderlock returns to its starting position.

Brake System

Anti-lock Brake System ABS/ESPContinental/Teves MK 25

The Touareg uses the MK 25 ABS/ESP sys-tem with Brake Assistant.

The hydraulic unit and control unit areintegrated into one unit

The active wheel sensor system detectsforwards and reverse travel

The ESP Sensor Unit G419 contains theSensor for Transverse Acceleration G200, theLongitudinal Acceleration Sensor G251 andthe Sender for Rotation Rate G202 in onehousing.

The Teves MK 25 ABS/ESP system has thefollowing functions:

Brake Assistant

Electronic Differential Lock

Traction Control System

Engine Braking Control

Hill Decline Assistant

Off-road ABS

Brake System

36

Active wheel speed senders areHall type senders.

These senders have the followingadvantages: They are capable of measuring

wheel speed accurately from avery low RPM

They are capable of distin-guishing between forward andreverse motions

ABS Control Module and Hydraulic Unit

37

Brake Assistant

The Brake Assistant is integrated into theABS Control Module. Since research hasshown that the majority of drivers do notpress the brakes hard enough in criticalsituations, the Brake Assistant takes over.

When a rapid rise in brake pressure issensed, the Brake Assistant will increase thebrake pressure to a level that exceeds thelocking limit, inducing ABS operation.

This enables maximum deceleration andshortens the vehicle stopping distance.

Electronic Differential Lock (EDL)

The Electronic Differential Lock (EDL) is a traction assistant that operates withoutdriver intervention.

Each wheel speed is monitored by the EDLsystem and spinning wheels are braked. Forexample, if the front right wheel is spinning,the brake will be applied to that wheel toslow it from spinning. This action sends thepower back through the center differential tothe opposite wheel.

This function operates on both front and rearaxles.

If the braking action is not sufficient to stabi-lize the vehicle, the motor torque is alsoreduced.

Hill Decline Assistant

The Hill Decline Assistant intervenes:

At speeds less than 12 mph (20 km/h)

On slopes greater than 20%

During forwards and reverse driving

When ESP is active

ESP intervention occurs when one wheelloses traction.

Using the ABS pump, the brakes are appliedat the wheels that have good traction. Thisacts against the vehicle acceleration causedby the lack of traction and keeps the vehiclespeed constant.

When this process is complete, the vehiclereturns to the previous driving speed.

Off-Road ABS

The off-road ABS permits the front wheelsto lock momentarily. The wedge action creat-ed in front of the front wheels supportsbraking.

The off-road ABS only acts:

At speeds less than 19 mph (30 km/h)

On the front wheels

When driving forward

Only in low range gear reduction

Brake System

Steering System

Overview

The standard power-assisted steering consists of the following components:

Rack-and-pinion steering box

Hydraulic pump (vane-type pump)

Hydraulic supply lines with large oilcooler

Steering Column

The steering column is electrically lockableand can be adjusted in the vertical and axialdirections.

The steering column is available with eithermanual or electric adjustment.

The travel range is 2 in. (50 mm) in the axialdirection and 1.6 in. (40 mm) in the verticaldirection.

Steering

38

39

Wheels and Tires

Wheels and Tires

The Tire Range

Collapsible Spare Tire

Tire Pressure Control System(Delayed Introduction)

The tire pressure control system monitorsthe tire pressure while driving using tireinflation valves with pressure-sensingelectronics and an antenna in each wheelhousing.

Tire Pressure Control

40

The pressure signals are sent through theCAN-BUS to the Tire Pressure MonitoringControl Module J502.

Incorrect tire pressure is displayed in theinstrument cluster driver information display.

41

The tire pressure control system in theTouareg monitors the pressure in all fourwheels.

The tire pressure control continuously moni-tors the tire pressure while driving and whenparked. A tire pressure sensor is attached toeach valve stem inside of the wheel. Thismeasures tire pressure and temperature atregular intervals.

A high frequency antenna is installed in each wheel housing to receive the radio data signal from each tire pressure sensor.

Data messages are received every 54 sec-onds in normal mode and every 850 millisec-onds in rapid-send mode. Rapid-send modeis triggered when the rate of pressure lossin the tire is greater than 0.2 bar/min.

This data is sent to the central control unitand evaluated.

The tire pressure control makes it possibleto always have the optimal air pressureinside the tires. This minimizes tire wear andfuel consumption.

The Tire Pressure Monitoring Control ModuleJ502 evaluates the tire pressures or tirepressure changes and sends the appropriatesystem messages to the driver informationdisplay in the instrument panel insert.

TPC provides the following benefits:

Constant display of tire pressure

Gradual pressure loss: The system informs the driver in time tobe able to correct the tire pressure.

Sudden pressure loss:The system warns the driver immediatelywhile driving.

Excessive pressure loss when the vehicleis stationary: The system warns the driver immediatelyafter the ignition is switched on.

Tire Pressure Control

To prevent system faults, the spare tire is not fitted with a wheel electronics module.

Tire Pressure Control

42

System Overview(Delayed Introduction)

43

Tire Pressure Sensors G222...G225

The tire pressure sensors have high trans-mission power, due to the thick tire wallsused on the Touareg. The sensors specificfor the Touareg can be recognized by theeight white stars on the top of the sensor.

Tire Inflation Connection

Vehicles with air suspension have a separatetire inflation connection. This is located underthe front right seat. It must only be used toinflate the spare tire or to add pressure tothe other tires on the Touareg.

Tire Pressure Control

Overview

The power of the Touareg engine is transmit-ted to the wheels via the full-time 4 wheeldrive, 4XMOTION system.

The front axle differential is a separate com-ponent from the engine/transmission assem-bly and is flexibly mounted to the sub-frame.In addition to being acoustically beneficial,this also makes it possible to mount thefront wheels further forward.

4XMOTION

44

Mounting the front wheels further forwardallows the overhang of the vehicle to kept asshort as possible, which in turn enhancesoff-road capabilities.

45

There are two drive equipment options forthe 4XMOTION system. The open rear dif-ferential is standard equipment while a lock-ing rear differential is available as an option.

4XMOTION

Open Rear Differential Optional Locking Rear Differential

The adjustable multi-plate clutch of the cen-ter differential is automatically controlled bythe Differential Control Module J646.

Torque is distributed from the engine to thefront and rear axles via the automatic trans-mission and transfer case.

During normal operation, torque is dividedequally between the front and rear axles.

The multi-plate center differential is allowedto disengage whenever the DifferentialControl Module determines a power differ-ential between the front and rear axles isrequired, for example, during cornering.

The driving force between the wheels of anindividual axle is distributed through theoperation of the Electronic Differential Lockfunction of the ABS.

The driver also has the option of locking thecenter differential (and optional rear differen-tial) by using a rotary switch in the centerconsole.

Locking the center differential with theswitch overrides automatic control andforces the front and rear axles to operate atthe same speed.

The transfer case consists of two planetarygear sets, a disk clutch, a locking device, arod and lever system for engaging the gearreduction, and a transfer chain. Power istransferred to the front differential via thechain drive.

Differential action between the front and rearaxles is accomplished via a straight cut gearplanetary gear set. The 2.7:1 gear reductionfor LOW off-road operation is accom-plished via a helical cut planetary gear set.

A single electric stepper motor actuates theengagement of the center differential lockand the gear reduction function. The steppermotor is controlled by the TransmissionControl Module.

46

The Transfer Case

he transfer case has three main functions inthe 4XMOTION system:

Transfer power from the transmission tothe front and rear axles

Provide differential action between thefront and rear axles

Provide gear reduction for LOW range

4XMOTION

47

4XMOTION The planetary gear sets for the center differ-ential and gear reduction as well as the com-ponents for the differential lock and gearreduction engagement are located in thetransfer case.

The stepper motor to actuate the differentiallock and gear reduction is mounted external-ly to the transfer case

An oil pump driven by the main shaftsupplies oil to all lubrication points throughthe hollow shaft.

48

Center Differential Lock

The center differential lock is a multiple-disclock that is actuated by an electric motor.The motor is controlled by the DifferentialControl Module J646 and is actuated eitherautomatically or can be overridden by engag-ing the lock with the lock switch in the cen-ter console

The electric motor turns a cam, which actu-ates a pivot arm. The pivot arm then pushesagainst an engaging plate. The engagingplate presses the disc pack together.

4XMOTION

The stepper motor is equipped with a plane-tary gear set which enables it to react quick-ly once the required apply torque has beencalculated by the Transmission ControlModule.

49

Center Differential Reduction Stage

Gear reduction for LOW is accomplishedby engaging or disengaging the reductionplanetary gear set in the transfer case. Agear reduction of 2.7:1 occurs whenengaged.

4XMOTION

The stepper motor that actuates the centerdifferential lock also operates the engage-ment of the gear reduction.

The stepper motor actuates the cam. Thecam has a curved inner track that moves apin, which in turn moves the shifter rail andshifter fork.

The shifter fork locks into a sliding sleeve.The inner part of this sliding sleeve is theinternal gear of the reduction planetary gearset. The internal gear is engaged with theassistance of synchronizer rings.

50

Rear Differential Lock

The rear differential lock operates in a similarmanner as the locking center differential. Anelectric motor operates a multiple disc clutchto force the axles to turn at the same speed.The motor is controlled by the DifferentialLock Control Module J647.

The electric motor is able to react quicklyand accurately by using a gear reduction setwhich moves a gear segment.

4XMOTION

51

4XMOTION

The gear segment has elongated ball sock-ets, which are deeper on one side than onthe other. These act like a ramp.

There are also elongated ball sockets in thecounter piece, which is held by the differen-tial housing. A disc holding ball bearings islocated between the gear segment and thecounter piece.

When both plates are rotated relative to eachother, they are pressed apart, creating anaxial movement. This applies pressure to 6studs which in turn engage the multiple discclutch by actuating a thrust plate.

If there is no current to the motor, the lock isopened by springs.

52

Electronic Drive Train Management

Electronic drive train management enablesthe off-road reduction stage to be engagedand the differential locks to be activatedeither automatically or manually. Settings areadjusted using the selector switch.

The "HIGH" setting is for on-road driving. Thedifferential locks are engaged automaticallydepending on the situation (e.g. icy condi-tions).

When driving off-road, the "LOW" settingcan be engaged while driving (up to 9 mph,or 15 km/h).

This engages the off-road reduction stage.The differential locks again react automatically.

Using the other two settings on the selectorswitch, the center differential lock and therear differential lock can be engaged manually.

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Control Strategy

The differential lock is engaged according tothe conditions, independent of the "HIGH"and "LOW" switch settings. The locking effectdepends on the engine speed, engine load,steering angle, accelerator position andwheel speeds. Using these parameters, theactuating motor sets the closing pressure ofthe multiple disc clutch to transfer calculatedtorque. Since the parameters change con-stantly, the torque to be transferred alsochanges constantly.

The differential locks must always operatewithout slipping, to prevent burning of thefriction plates.

The rotary switch is used to engage or dis-engage the reduction stage, and this sendsthe signal to the control unit.

To either engage or disengage the reductionstage, the transmission selector lever mustbe in Neutral.

The reduction stage will only engagewhen the vehicle speed is less than 9 mph(15 km/h). It will only disengage when thevehicle speed is less than 25 mph (40 km/h).

If the time limit expires before these param-eters are changed, the control unit assumesthat the shift sequence is implausible.

To protect the automatic transmission, thedriving speed and the engine speed arelimited 50 mph (80 km/h) when the reduc-tion stage is engaged.

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Special Tools

Special Tools

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Knowledge Assessment

An on-line Knowledge Assessment (exam) is available for this Self-Study Program.

The Knowledge Assessment may or may not be required for Certification.

You can find this Knowledge Assessment at:

www.vwwebsource.com

From the vwwebsource.com Homepage, do the following:

-- Click on the Certification tab

-- Type the course number in the Search box

-- Click Go! and wait until the screen refreshes

-- Click Start to begin the Assessment

For assistance, please call:

Certification Program Headquarters

1-877-CU4-CERT

(1-877-284-2378)(8:00 a.m. to 8:00 p.m. EST)

Or E-mail:

Comments@VWCertification.com

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Volkswagen of America, Inc.3800 Hamlin RoadAuburn Hills, MI 48326Printed in U.S.A.April 2003