Defender. Manual — part 49
a reservoir that also acts as a cooler.
The steering box houses a self neutralizing rotary valve which is part of the worm/valve assy and an hydraulic
piston/rack to assist the mechanical operation. The rotary valve which is operated by movement of the steering wheel,
directs fluid pressure to the appropriate side of the hydraulic piston/rack to provide assistance.
Rotary valve operation
Rotary valve at neutral
The rotary valve assembly comprises a worm (1), valve sleeve (2), input shaft (4) and torsion bar (5).
The valve sleeve is retained inside the worm by a trim screw (3), and incorporates valve ports in its inner bore. The
input shaft is attached to the steering wheel via a 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, holds the valve ports in neutral
alignment when there is no demand for assistance.
When there is no demand for assistance 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 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.
CAUTION: To avoid excessive fluid temperatures which could damage the oil seals, the steering must not be held
on full lock for more than 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.
Pump and regulator valve operation
No demand for assistance
Item
Part Number
Description
1.
-
Reservoir
2.
-
Pump
3.
-
Pressure control ball valve and spring
4.
-
Flow control valve and spring
4.
-
Press fit plug (ball bearing)
5.
-
Restrictor
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).
With no demand for assistance 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).
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).
Assistance demanded
As soon as the steering wheel is released after making a turn, the system reverts to the condition seen in J6292 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.
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Steering System - General Information - Steering System
Diagnosis and Testing
Symptom Chart
Power steering pressure faults
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.
Excessive pressure in the system is almost always caused by a faulty relief valve in the PAS pump.
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.
Symptom
Possible Sources
Action
Insufficient power assistance
Fluid leaks
Check for leaks, top-up reservoir.
Incorrect system pressures
Carry out pressure test.
Power steering pump drive belt
Check for contamination and/or correct tension.
Steering linkage faults
Symptom
Possible Sources
Action
Excessive kickback through
steering wheel
Faulty steering damper
Replace steering damper
Looseness or free play in
steering linkage
Check steering linkage and replace worn or faulty
components.
Looseness or worn bushes in
front suspension
Check suspension and replace worn or faulty
components.
When replacing suspension bushes, ALL bushes and
fixings must be replaced.
Swivel hub resistance incorrect
Check swivel pin bearing pre-load.
Fluid leaks
CAUTION: The steering wheel must not be held on full lock for more than 30 seconds in one minute, as this may
overheat the fluid and cause damage to the oil seals.
Symptom
Possible Sources
Action
Fluid leaks from
steering box
Excessive system pressure
Replace power steering pump. If problems persist,
overhaul the steering box.
Power steering fluid
leaks
Incorrect fluid level.
Refill or drain to the correct level.
Leak from hoses and/or joints.
Slacken and re-torque unions. Replace faulty pipes or
hoses.
Fluid escaping from filler cap.
Bleed power steering system.
Worn or damaged seal in steering
system component.
Replace faulty seal(s).
Insufficient power assistance - normal castor return action
Symptom
Possible Sources
Action
Insufficient
power
assistance
Incorrect tire pressures or
incorrect type of tire
Adjust tire pressures and/or replace tires.
Low fluid level or air locks
in the system
Top-up fluid level, bleed the fluid system.
Incorrect system
pressures.
Check system pressures and bleed system. If fault persists, replace
power steering pump and/or overhaul steering box.
Steering heavy/stiff - poor castor return action
Symptom
Possible Sources
Action
Stiff or heavy
steering
Incorrect type of tire or incorrect
pressure.
Fit correct tires or inflate to correct pressure.
Universal joint incorrectly aligned
or seized.
Free off or replace universal joint, align correctly.
Steering box incorrectly adjusted.
Adjust steering box.
REFER to:
Steering Gear Adjustment
(211-00 Steering System -
General Information, General Procedures).
Steering ball joints seized.
Replace seized components.
Swivel pins require lubrication or
bearing preload resetting.
Lubricate swivel pins or set bearing preload.
Steering box worn or seized.
Overhaul steering box.
Steering excessively light/sensitive. Excessive free play at steering wheel
WARNING: Adjustments of steering box should not be required while in warranty period. If box is within warranty,
it must be returned to manufacturer. No attempt must be made to introduce backlash.
Symptom
Possible Sources
Action
Light
steering/excessive
free play
Incorrectly adjusted steering box
Adjust steering box.
REFER to:
Steering Gear Adjustment
(211-
00 Steering System - General Information,
General Procedures).
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