Range Rover Classic. Manual — part 97
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
57
STEERING
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 - Go to 8.
NO -
Correct idle speed -
If 3.9
See ENGINE TUNING DATA,
Information, Engine 3.9 - V8i
If 4.2
See ENGINE TUNING DATA,
Information, Engine - 4.2 V8i
If Tdi
See ENGINE TUNING DATA,
Information, Engine - 300 Tdi
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.
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