System Description - 1990 Model Year On Page 6

System Description - 1990 Model Year on

CAUTION: The hydraulic power system uses CASTROL HYDRAULIC SYSTEMS MINERAL OIL (HSMO). Use of other oil may result in system failure. Store the HYDRAULIC SYSTEM MINERAL OIL ONLY IN ITS ORIGINAL CONTAINER. Keep the container clean and tightly closed as contamination will result in mechanical failure or costly repairs.

The hydraulic power steering and payload compensated levelling system uses a power hydraulic system to provide power assisted steering operation and can also provide self-levelling, which automatically adjusts the vehicle trim to maintain the correct body attitude with respect to the road. Trim adjustments undertaken by the system are limited to those which compensate for laden/unladen (bulk load) changes over the rear axle rather than those experienced when cornering or negotiating undulating road surfaces.

CAUTION: Since the system corrects the vehicle trim to compensate for rear axle load changes, it is possible to grossly overload the vehicle without any perceptible difference in trim height. It is essential that the specified vehicle weight is not exceeded.

The system, which responds to trim deflections maintained over and above a period of 20 seconds, contains the following items:

Suspension-up, down and unloader solenoid valves: These valves, under ride height sensor control, increase or decrease the oil pressure applied to the struts. Trapped line pressure valve (integral part of down solenoid valve assembly): A non-return valve which ensures that a minimum oil pressure of 27 bar (400 lb./sq.in.) is retained within the levelling system.
Pressure relief valve: permits high pressure oil to return to the reservoir in the event of gross vehicle overloading or the system becoming over-pressurized.
Pump: a three piston radial device which operates at 0.75 times engine speed and delivers 0.7 litre/min (0.153 gal/min) at 600 rev/min.
Oil reservoir: a vessel which stores a supply of mineral oil for use by the system.
Levelling strut: is an integral part of the rear suspension which extend and retract in response to oil pressure changes made by the suspension-up/down valves.
Ride height sensor: a device which monitors the body-to-axle distance and controls the suspension-up/down valves to obtain the correct trim.

Fig. 2 Power Hydraulic Circuit - 1990 MY on (schematic only):

A schematic illustration ofthe power hydraulic circuit for vehicles from 1990 model year onward, is shown in Fig.2.