wheel torque LAND ROVER DISCOVERY 1999 User Guide

REAR AXLE
51-14 OVERHAUL
42.Fit adjusting nuts, tighten crown wheel side nut
to 22 Nm (16 lbf.ft). Ensure opposing nut is
loose.
43.Position DTI to check crown wheel backlash.
Adjust opposing nut to obtain correct crown
wheel backlash.
44.Rotate pinion in both directions to settle
bearings.
45.Measure in 3 places to obtain correct crown
wheel backlash.
NOTE: Crown wheel backlash should be within
0.076 mm - 0.177 mm (0.003' - 0.007').
46.Align adjusting nuts to next roll pin slot, do not
loosen nuts to align slots.
47.Tighten bearing cap bolts to 90 Nm (66.5 lbf.ft).
48.Secure adjusting nuts with new roll pins.
49.Apply Prussian Blue to crown wheel teeth to
check tooth contact.50.Rotate pinion several times to obtain full tooth
contact.
51.A = Normal pattern, the drive pattern should be
centred on the gear teeth. The coast pattern
should be centred on the gear teeth but may be
towards the toe. There should be some
clearance between the pattern and the top of
the gear teeth.
52.B = Backlash correct, thinner pinion shim
required.
53.C = Backlash correct, thicker pinion shim
required.
54.D = Pinion shim correct, decrease backlash.
55.E = Pinion shim correct, increase backlash.
56.Note assembly Torque to Turn when checking
tooth contact. Total Torque to Turn should not
exceed 10.85 Nm (8 lbf.ft).
Reassembly
1.Fit differential assembly.

STEERING
57-6 DESCRIPTION AND OPERATION
Tilt adjustment
The column tilt adjuster lever mechanism is located on the LH side of the steering column and allows the upper column
tube, nacelle and steering wheel assemblies to be tilted up or down a maximum of 7.5° or 47 mm (NAS vehicles have
a smaller range of movement than the ROW vehicles).
The pawl of the mechanism is attached to the lower column and is allowed to pivot, a toothed quadrant is fixed to the
upper column tube.
When the lever on the LH side of the steering column is raised the mechanism releases the pawl from the toothed
quadrant, this allows the column to be moved. When the lever is released two return springs pull the pawl into
engagement with the toothed quadrant.
Steering column lock (All except NAS)
The steering column lock houses the ignition switch, ignition illumination light ring, key lock barrel and the alarm
passive coil. The steering lock is attached to the upper column with two shear bolts. The bolts are tightened to a
torque which shears off the heads of the bolts preventing easy removal of the steering lock.
The steering lock operates by a bolt, which emerges when the ignition key is turned to position 'O' and the ignition key
removed. The bolt engages in a lock collar located on the upper shaft in the upper column tube. The lock collar is
attached to the upper shaft by a 'wave form' interference ring. If a high torque is applied via the steering wheel with
the lock engaged, the lock collar will slip on the upper shaft. This prevents damage to the steering lock, yet still
prevents the vehicle from being driven.
Steering column lock (NAS only)
The steering column lock houses the ignition switch, ignition illumination light ring, key lock barrel and the alarm
passive coil. The steering lock is attached to the upper column with two shear bolts. The bolts are tightened to a
torque which shears off the heads of the bolts preventing easy removal of the steering lock.
The steering column lock operates by a bolt, which emerges when the ignition key is turned to position 'O' and the
ignition key removed. The bolt engages in a groove machined into the upper shaft in the column tube.
Steering wheel
The steering wheel comprises a cast centre and wire frame onto which the soft polyurethane foam is moulded. The
steering wheel is located on the upper column shaft by a spline and is secured with a nut. A remote radio control switch
(if fitted) is located on the LH side of the steering wheel, a cruise control switch may be located on the RH side. Horn
switches are located on each side of the centre of the steering wheel and protrude through the airbag module cover.
Both switches are connected by wires to the rotary coupler connector.
Intermediate shaft
One end of the intermediate shaft is attached to the steering column lower shaft by a splined universal joint and a bolt,
the universal joint is part of a rubber coupling assembly. The rubber coupling assembly is covered by a heat shield
and connects to the lower section of the intermediate shaft via a decouple joint. The rubber coupling reduces the
shocks felt by the driver through the steering wheel. A second universal joint on the other end of the intermediate shaft
is held in by a bolt. The universal joint is splined and engages with the splined rotor (input) shaft of the steering box.
The decouple joint consists of a metal plate that has open ended slots, the plate is bolted through the slots into the
other half of the decouple joint. The top half of the decouple joint has a slot that accepts the lower section of the
intermediate shaft. The slotted metal plate clamps the lower section of the intermediate shaft to the top section. An
indicator clip is installed between the slotted metal plate and the top half of the decouple joint.
If the intermediate shaft is compressed in an accident, the slotted metal plate in the decouple joint will disengage if
sufficient force is applied to the front end of the shaft. If the forces involved do not disengage the shaft, the red
indicator clip located in the decouple joint will break off if the shaft moves. The intermediate shaft cannot be repaired
and must be replaced as an assembly if accident damage occurs.

STEERING
DESCRIPTION AND OPERATION 57-11
Rotary control valve in demand mode
1Worm gear
2Torsion bar
3Valve sleeve
4Pin5Input shaft and valve rotor
6Piston/rack
7Coarse spline
8Spline (torque shaft to worm gear)
When the steering wheel and input shaft is turned steering resistance transmitted to the worm causes the torsion bar
to be wound up and the valve ports in the valve rotor and valve sleeve to be aligned for a right or left turn. The
alignment of the valve ports directs fluid pressure 'A' from the PAS pump to one side of the piston/rack . The other
side of the piston/rack is now connected to return 'B' (due the valves port alignment) and displaced fluid returns to the
reservoir. The pressure difference in the cylinder on each side of the piston gives the power assistance to move the
rack and so turn the steering.
The greater the resistance of the road wheels to the steering rotary movement, the greater torque acting on the torsion
bar and input shaft causing greater changes of alignment of the ports in the valve. As the change of alignment
becomes greater, the fluid pressure passing to the applicable side of the piston/rack increases.
Only when the steering wheel stops turning and the torsion bar has unwound, will the valve rotor return to the neutral
position. In the neutral position the fluid circulates through the ports in the valve rotor and valve sleeve and back to
the reservoir where it is cooled.

BRAKES
DESCRIPTION AND OPERATION 70-5
Description
General
The brakes consist of front and rear disc brakes operated by a diagonally split, dual circuit hydraulic system with
vacuum servo power assistance. The system incorporates the following control functions as standard on all models:
lAnti-lock Brakes (ABS), to prevent road wheels locking during brake application.
lElectronic Brake Distribution (EBD), to control distribution of hydraulic pressure between front and rear axles.
Replaces mechanical pressure limiting valve of previous systems.
lElectronic Traction Control (ETC), to maintain even torque distribution to the road wheels.
lHill Descent Control (HDC), to provide controlled descent ability in off road conditions.
Hydraulic system schematic
1Master cylinder/brake servo assembly
2Brake pedal
3ABS modulator
4Rear brake5Front brake
6Hydraulic circuit
aPrimary
bSecondary
For normal brake operation, brake pedal movement is assisted by the brake servo assembly and transmitted to the
master cylinder assembly. The master cylinder assembly converts brake pedal movement to hydraulic pressure.
Primary and secondary brake pipe circuits supply the hydraulic pressure to the brakes via the ABS modulator: the
primary circuit supplies the front left and rear right brakes; the secondary circuit supplies the front right and rear left
brakes. Vacuum for the brake servo assembly is obtained from the engine inlet manifold (V8 models) or a vacuum
pump (diesel models), through a vacuum line and non return valve. To reduce operating noise, sleeving is installed
on some of the brake pipes in the engine compartment and the pipes are located in sprung pipe clips.
For all control functions, the ABS modulator regulates the hydraulic pressure to the brakes to control the speed of all
four wheels, either individually or in axle pairs. Operation of the ABS modulator is controlled by the Self Levelling and
Anti-lock Braking Systems (SLABS) ECU. The SLABS ECU also operates warning indications in the instrument pack
to provide the driver with status information on each function.

BRAKES
DESCRIPTION AND OPERATION 70-17
SLABS ECU
The SLABS ECU is attached to a bracket behind the front passenger glovebox. Brake related inputs are processed
by the SLABS ECU, which then outputs control signals to the ABS modulator. Five electrical connectors interface the
SLABS ECU with the vehicle wiring.
SLABS ECU connector pin details
Connector/Pin
No.Description Input/Output
C0504
1 Battery supply Input
2 Ignition supply Input
3 Road speed Output
4 Rough road (V8 models only) Output
5 K line (diagnostics) Input/Output
7 Reverse gear Input
8 Return pump monitor Input
9 Brake warning lamp Output
10 Engine data (throttle position, torque, engine type, gearbox type) Input
11 Transfer box range Input
12 Earth-
13 ETC warning lamp Output
14 HDC switch Input
15 Neutral selected (automatic gearbox only) Input
16 HDC fault warning lamp Output
17 HDC information warning lamp Output
18 ABS warning lamp Output
C0505
1 Front left wheel speed Input
2 Front left wheel speed Input
3 Rear right wheel speed Input
4 Front right wheel speed Input
5 Front right wheel speed Input
6 Rear right wheel speed Input
7 Rear left wheel speed Input
8 Rear left wheel speed Input
C0506
1 Front left outlet solenoid valve Output
2 Front left inlet solenoid valve Output
3Earth-
4 Front right outlet solenoid valve Output

BRAKES
DESCRIPTION AND OPERATION 70-21
ETC
The ETC function uses brake intervention to prevent wheel spin and maintain even torque distribution to the wheels.
ETC is automatically enabled while the brakes are off at speeds up to 62.5 mph (100 km/h), and operates the brakes
either individually or in axle pairs:
lAt speeds up to 31.3 mph (50 km/h), ETC uses individual brake intervention to maintain even torque distribution
between wheels on the same axle.
lVehicles up to 03 model year – At speeds between 0 and 62.5 mph (0 and 100 km/h), ETC also uses brake
intervention in axle pairs to maintain even torque distribution between the front and rear axles. In effect, this mode
of operation replaces the centre differential lock of the transfer box which, although still incorporated, is non
operational under normal driving conditions.

+ TRANSFER BOX - LT230SE, DESCRIPTION AND OPERATION, Description. If the centre differential
lock is in the locked condition, the SLABS ECU illuminates the ABS and ETC warning lamps and inhibits the ETC
function (the ABS, EBD and HDC functions are retained, but at degraded performance levels).
lVehicles from 03 model year (with differential lock fitted) – At speeds between 0 and 62.5 mph (0 and 100
km/h), ETC uses brake intervention in axle pairs to maintain even torque distribution between the front and rear
axles. If the centre differential lock is in the locked condition, the differential lock warning lamp in the instrument
pack is illuminated. The ABS, EBD, ETC and HDC functions are retained, but with revised parameters to suit the
locked differential.
While the ETC function is enabled, if the SLABS ECU detects a wheel accelerating faster than the average, indicating
loss of traction, it operates the ABS modulator in the active braking mode. Depending on the vehicle speed, active
braking is employed for either the brake of the affected wheel or for both brakes on the affected axle, until all four
wheels are driven at approximately the same speed again. During active braking the SLABS ECU also illuminates the
ETC warning lamp, for a minimum of 2 seconds or for the duration that ETC is active. ETC operation is desensitised
during 'hard' cornering.
HDC
HDC uses brake intervention to provide a controlled descent ability in off road conditions when engine braking is
insufficient to maintain a comfortable speed. This allows the driver to leave HDC selected and to control the vehicle's
descent speed, down to the system's minimum target speed, using only the accelerator pedal. The HDC function is
selected on/off by a switch on the fascia. When selected on, HDC is enabled in all forward gears and reverse provided:
lVehicle speed is below 31.3 mph (50 km/h).
lThe transfer box is in low range.
lOn manual gearbox vehicles, the clutch is engaged.
When HDC is enabled, the HDC information warning lamp illuminates. If HDC is selected outside the above
conditions, the HDC information warning lamp flashes and the audible warning sounds continuously.
When HDC is enabled, the SLABS ECU calculates a target speed from the throttle position element of the engine data
input, and compares this with actual speed. If the actual speed is higher than the target speed, the SLABS ECU
operates the ABS modulator in the active braking mode to slow the vehicle down to the target speed. While the braking
force is being applied, the SLABS ECU also energizes the brake lamp relay to put the brake lamps on. Active braking
is discontinued while vehicle speed is below the target speed or if the foot brakes are applied. Applying the foot brakes
during active braking may result in a pulse through the brake pedal, which is normal.
During active braking, the brakes are operated predominantly on the wheels of the leading axle, but if that is not
sufficient to achieve the required deceleration the brakes of the trailing axle are also applied. The deceleration rate is
dependent on the speed differential between initial vehicle speed and the target speed. The deceleration rates are
relatively low at higher speed differentials, then progressively increase as vehicle speed approaches the target speed.
Anti-lock braking is also enabled during active braking, but at very low speeds some wheel lock can occur.
The target speed increases as the accelerator pedal is pressed, from a programmed minimum with the accelerator
pedal released, up to a maximum of 31.3 mph (50 km/h). For any given accelerator pedal position, while travelling
uphill or on level ground the target speed is always greater than the corresponding vehicle speed, which allows the
vehicle to be driven normally without HDC intervention. However, when travelling downhill, the gravitational effect on
the vehicle means that for any given accelerator pedal position the target speed is less than the corresponding vehicle
speed, and HDC intervenes to limit vehicle speed to the target speed.