Discovery 2. Manual — part 170

STEERING

DESCRIPTION AND OPERATION

57-15

As the pump rotor rotates towards the pump inlet the volume between the roller vanes and the pump housing
increases, this action causes a depression in the chamber between the pump roller vanes and the housing. As the
rotation continues the chamber is opened to the pump inlet, and the depression in the chamber causes fluid to be
drawn in. The roller vanes continue past the inlet port, closing off the inlet port and trapping the fluid in the chamber
between the rollers and the pump housing.

The internal 'cam' shape of the pump housing causes the rollers to move closer together as the pump rotor rotates
towards the outlet port. The reduced volume of the chamber between the roller vanes causes the fluid to become
pressurised. When the chamber is opened to the outlet port of the pump the fluid escapes at high pressure. The roller
vanes continue turning and go past the outlet port, closing off the chamber between the two roller vanes.

As rotation continues the inlet sequence begins again. The inlet and pressurisation/outlet sequences continue as the
pump rotates, and is repeated between each two roller vanes. The pump is a positive displacement type and the
potential pump output increases with engine (drive pulley) speed. The pressure relief and flow control valve regulates
flow/pressure by diverting fluid back to the pump inlet through internal recirculation passages in the pump body.

Steering damper
The steering damper is located behind and just below the first cross member of the chassis. The ends of the steering
damper have steel 'eyes' welded on, rubber bushes are installed in each 'eye'. The steering damper is attached
between brackets on the chassis rail and the drag link. Each end of the steering damper is secured by a bolt and
locknut. The hydraulic damper absorbs shocks in the steering, caused by road wheel deflections when operating on
rough terrain.

STEERING

57-16

DESCRIPTION AND OPERATION

Operation

Hydraulic fluid is supplied to the PAS pump inlet from the PAS reservoir, the PAS pump draws in and pressurises the
fluid. The PAS pump self regulates internal flow rates and operating pressure, and supplies pressurised fluid from the
PAS pump outlet to a rotary control valve in the steering box. At neutral the fluid is circulated by the PAS pump and
flows around the system at a lower pressure and a constant flow rate. With most of the fluid being returned to the
reservoir the pressure inside the system remains very low. When a control input turns the rotary control valve in the
steering box, pressure in the system will rise as the control valve directs fluid to give power assistance.

The action of turning the steering wheel turns the steering column and intermediate shaft. The intermediate shaft turns
the input shaft of the steering box. The input shaft moves the rotary control valve in the steering box, the rotary valve
controls the pressure used inside the steering box for power assistance. The input shaft also turns a worm gear, the
worm gear acts on a roller attached to the output shaft. As the worm gear turns the roller, the roller travels along the
lands of the worm gear. As the roller is attached to the output shaft the output shaft turns.

As the output shaft of the steering box turns, hydraulic pressure is supplied via the rotary control valve to the steering
box. The hydraulic pressure acts on a rack that assists with the movement of the output shaft of the steering box. A
drop arm is attached to the output shaft of the steering box. The drop arm is connected to a drag link by a ball joint.
The drag link is connected via ball joints to one front steering knuckle and road wheel. A track rod connected to this
steering knuckle links the two steering knuckles together. As one steering knuckle and road wheel is turned by the
drag link, the other steering knuckle and wheel is moved by the track rod.

STEERING

ADJUSTMENTS

57-17

ADJUSTMENTS

Steering box - check and adjust

$% 57.10.13

Check

1. Raise front of vehicle.

WARNING: Do not work on or under a
vehicle supported only by a jack. Always
support the vehicle on safety stands.

2. Remove nut securing drag link to drop arm.
3. Using LRT-57-036, break taper joint and

release drag link.

4. Ensure steering is centralised.
5. With the drop arm held, check for rotational

movement at the intermediate shaft universal
joint. If any movement exists, the steering box
requires adjusting.

Adjust

1. Loosen lock nut on steering box adjuster and

tighten adjuster until movement is removed at
universal joint.

CAUTION: Ensure that steering box is
centralised before adjustment. Never over
adjust, free play should just be eliminated.

2. When adjustment is correct, hold the adjuster

and tighten adjuster locknut.

3. Turn steering wheel from lock to lock and check

no tightness exists.

4. Fit drag link to drop arm, and tighten nut to 80

Nm (59 lbf.ft).

5. Remove stands and lower vehicle.

STEERING

57-18

ADJUSTMENTS

Hydraulic system - bleed

$% 57.15.02

Bleed

1. Clean PAS fluid reservoir around filler cap and

fluid level indicators.

2. Remove filler cap from PAS fluid reservoir. If

necessary, fill PAS fluid reservoir to upper level
indicator with recommended fluid.

+

CAPACITIES, FLUIDS,

LUBRICANTS AND SEALANTS, Fluids.

CAUTION: Ensure no dirt is allowed to enter
the steering reservoir when the cap is
removed.

3. Start engine and run to normal operating

temperature.

4. Position container to catch fluid spillage from

steering box.

5. With engine at idle speed, and an assistant

turning the steering from lock to lock, loosen
bleed screw on top of steering box. Keep PAS
fluid reservoir topped up and allow all air to
bleed from system. When fluid from bleed
screw is free of air, tighten bleed screw.

CAUTION: Do not hold steering at full lock
for longer than 10 seconds.

6. Stop engine.
7. Clean spilled PAS fluid from steering box and

surrounding area.

CAUTION: Power steering fluid will damage
paint finished surfaces. If spilled,
immediately remove fluid and clean area
with water.

8. Check fluid level in PAS fluid reservoir and fill to

upper level mark. If fluid is aerated, wait until
fluid is free from bubbles.

9. Fit PAS fluid reservoir filler cap.

Steering linkage - centralise

$% 57.35.05

The following procedure assumes that the front
wheel alignment is correctly adjusted.

Adjust

1. Raise front of vehicle, and position the road

wheels at straight ahead.

WARNING: Do not work on or under a
vehicle supported only by a jack. Always
support the vehicle on safety stands.

2. Remove nut securing drag link to drop arm.

Using tool LRT-57-036 break taper joint and
release drag link from drop arm.

3. Fit centralising bolt to steering box and ensure

that front road wheels are in the straight ahead
position.

4. Loosen clamp bolts on drag link.