1995 LAND ROVER DISCOVERY Workshop Manual

57STEERING
2
DESCRIPTION AND OPERATION

STEERING
3
DESCRIPTION AND OPERATION Steering column components
1. Upper shroud
2. Column harness
3. Cruise control switch (if fitted)
4. Steering wheel and nut
5. Rotary coupler
6. Column switch
7. Shear bolts
8. Switch saddle
9. Upper steering column
10. Universal joint
11. Universal joint bolt
12. Steering column lock assembly13. Lower shroud
14. Column lock/ignition
15. Air bag mounting bracket (if fitted)
16. Air bag module
17. Steering pad (non-airbag)
18. Lower shaft
19. Rubber coupling
20. Compression joint
21. Universal joint
22. Universal joint bolt

57STEERING
4
DESCRIPTION AND OPERATION
Power steering box components
1. Housing complete with sector shaft bearings
2. Cover plate complete with bearing
3. Sector shaft
4. Hydraulic piston/rack
5. Worm/valve and torsion bar assembly
6. Shims for centralizing worm/valve
7. Ball race (2)
8. 'Teflon' seals for valve sleeve (3)
9. Bearing adjuster, locknut and seal
10. Worm shaft pressure seal, circlip and dirt
excluder11. 'Teflon' and rubber seal for piston
12. End cover seal and snap ring
13. Adjustment components for piston/rack
14. Hydraulic pipe
15. Bleed screw
16. Sector shaft adjustment lock nut with seal
17. Cover plate bolts (4)
18. Cover plate seal
19. Seal, washer and backup seal
20. Circlip and dust cover

STEERING
5
DESCRIPTION AND OPERATION Rotary valve operation
The rotary valve assembly seen in RR3620M
comprises the worm (1), the valve sleeve (2), the input
shaft (4) and the torsion bar (5).
The valve sleeve is retained inside the worm by the
trim screw (3), and incorporates valve ports in its inner
bore. The input shaft is attached to the steering wheel
via the steering shaft and steering column and
incorporates valve ports in its outer diameter to align
with those in the sleeve. The torsion bar which is
secured to the worm and input shaft with pins (6) at
each end (later models use one pin at input shaft
end), holds the valve ports in neutral alignment when
there is no demand for assistance.No demand for assistance (Valve at neutral)
When there is no demand for assistance as seen in
RR3620M, the torsion bar holds the input shaft and
sleeve valve ports in neutral relationship to one
another, allowing equal pump pressure A to both
sides of the piston/rack (9). Any excess fluid flow from
the pump returns to the reservoir via B.
Rotary valve at neutral

57STEERING
6
DESCRIPTION AND OPERATION Demand for assistance (Valve misaligned)
When the steering wheel and input shaft is turned,
steering resistance transmitted to the worm causes
the torsion bar to be twisted and the valve ports to be
misaligned for a right or left turn. The misalignment of
the valve ports directs all fluid pressure A to one side
of the piston only and allows displaced fluid B on the
other side.When demanding maximum assistance, any
excessive fluid output from the pump due to high
pump speed, will circulate through the regulator valve
located in the pump unit, causing the temperature of
the fluid and the pump to rise rapidly.
To avoid excessive fluid temperatures which could
damage the oil seals, the steering must not be held on
full lock for more that 30 seconds in one minute.
Only when the steering wheel and the demand for
assistance is released, will the torsion bar return the
valve to neutral, allowing the fluid to circulate through
the reservoir where it is cooled.
In the unlikely event of mechanical failure of the
torsion bar, a coarse splined connection (7) between
the input shaft and worm, ensures steering control is
maintained sufficient to allow the vehicle to be
recovered.
Rotary valve misaligned

STEERING
7
DESCRIPTION AND OPERATION Pump and regulator valve operation
The pump which is belt driven from the engine is an
eccentric roller type and also houses the pressure
regulator and flow control valve. The pressure is
controlled by a spring loaded ball valve 3 which is
housed inside the flow control valve piston 4.
No demand for assistance High flow through box -
Low pressure
With no demand for assistance as illustrated in
RR3568M the rotary valve in the steering box acts as
a pressure relief valve, allowing fluid A to flow freely
through the steering box and back to the reservoir and
pump inlet B.
No demand for assistance
1. Reservoir
2. Pump
3. Pressure control ball valve and spring
4. Flow control valve and spring
5. Press fit plug (ball bearing)
6. Restrictor
The ball plug item 5 is pressed into the valve 4
during manufacture and determines the opening
pressure of pressure relief valve 3.No flow, through box - High pressure
When the steering is turned, the rotary valve
effectively stops all fluid flow through the steering box,
thus causing an increase in pressure A. This increase
in pressure is felt in the flow control valve spring
chamber where, at a pre-determined pressure the
relief valve 3 will open and allow the pressure to
escape. The fall in pressure in the flow control spring
chamber, allows the flow control valve to move to the
right, which in turn allows pump output A to escape
directly into the pump inlet B, as seen in RR3569M.Assistance demanded
As soon as the steering wheel is released after
making a turn, the system reverts to the condition
seen in RR3568M and the road wheels are returned
to the straight ahead position by the mechanical
steering geometry.
In the event of any hydraulic failure steering control
though heavy, will be maintained through the
mechanical components in the steering box.

STEERING
1
FAULT DIAGNOSIS INSUFFICIENT POWER ASSISTANCE
1.Is fluid level correct?
YES - go to 3.
NO - Fill/bleed sytem
2.Is problem a leak?
YES - Diagnose.
See Power Steering Fluid
Leaks
NO - continue
3.Is drive belt tension correct?
YES - go to 5.
NO - retension.
See ENGINE, Repair, Drive
Belt
4.Is problem resolved?
YES - end
NO - continue
5.Carry out pressure test at idle and 1000 rev/min.
See Power Steering System - Test
6.Is correct pressure achieved?
YES - steering box defective
Not at any speed go to 9.
Not at idle go to 7.
7.Is idle speed correct?
YES- Goto8.
NO - Correct idle speed -
If 3.9
See ENGINE TUNING DATA,
Information, Engine 3.9 V8i
If TdiSee ENGINE TUNING DATA,
Information, 300 Tdi Engine
If MpiSee ENGINE TUNING DATA,
Information, Engine - Mpi - 2.0 Litre
8.Is problem resolved?
YES - end
NO - go to 9.
9.Bypass steering box using adaptor tap
LRT-57-001
10.Is correct pressure obtained?
YES - defective steering box
NO - defective steering pump
CAUTION: Do not hold steering wheel on
full lock for more than 30 seconds in any
one minute to avoid overheating fluid and
possibly damaging seals.
NOTE: 1. Excessive pressure in the
system is almost always caused by a
faulty relief valve in the PAS pump.
NOTE: 2. Insufficient pressure in the
system is usually caused by low fluid level
or PAS pump drive belt slip, or one of the
following: PAS system leaks, faulty PAS pump
relief valve, fault in steering box valve and worm
assembly, leak at piston in steering box, worn
components in PAS pump or box.

57STEERING
2
FAULT DIAGNOSIS POWER STEERING SYSTEM - TEST
NOTE: If steering lacks power assistance.
Check pressure of hydraulic pump before
fitting new components. Use fault
diagnosis chart to assist in tracing faults.
A. Steering box.
B. Steering pump.
C. Existing hose, steering box to pump.
D. Hose LRT-57-030.
E. Test adaptor LRT-57-001.
F. Pressure gauge LRT-57-005.
G. Thread adaptor LRT-57-004.
H. Thread adaptor LRT-57-022.Procedure
1.A hydraulic pressure gauge and test adaptor is
used to test power steering system. This gauge
is able to measure 140 kgf/cm
2. The maximum
power steering system pressure is 77 kgf/cm2.
2.Some fault conditions of hydraulic pump may
obtain pressures up to 105 kgf/cm
2. Pressure on
gauge is same pressure being exerted upon
steering wheel. When testing, turn steering
wheel gradually while reading pressure gauge.
3.Check and maintain maximum fluid level of
reservoir.
4.Examine power steering units and connections
for leaks. All leaks must be rectified before
attempting to test the system.
5.Check steering pump drive belt tension.
See
ENGINE, Repair, Drive Belt
6.Assemble test equipment and fit to vehicle, as
shown in RR3959M.
7.Open tap of adaptor.
8.Bleed system, take care not to overload
pressure gauge.
9.With system in good condition, pressures should
be:
(A) Steering wheel held on full lock and engine
running at 1,000 rev/min, 70 to 77 kgf/cm
2.
(B) Steering wheel held on full lock and engine
idling, 28 kgf/cm
2.
Checks should be carried out on both full lock
positions.
CAUTION: Do not maintain this pressure
for more than 30 seconds in any one
minute to avoid overheating fluid and
possibly damaging seals.
10.Release steering wheel and with engine idling.
Pressure should read below 7 kgf/cm
2.
11.If pressures differ to those given a fault exists.
12.To determine if fault is steering box or pump.
Close adaptor tap for a maximum five seconds.
13.If gauge does not register specified pressure,
pump is faulty.
14.Fit a new pump, bleed system and repeat test. If
low pressure or a substantial imbalance exists,
fault is in steering box valve and worm
assembly.