HYDROLASTIC SUSPENSION NOTE.- On models with Hydrolastic suspension, an auxiliary coil spring is located between the rear end Of each of the rear radius arms and the body to limit the ann movement on rebound.
Depressurising and Repressurising the System Before any major work can be carried out on the suspension or its components, the Hydrolastic system must be depressurised.
For this operation a special piece of equipment, namely a Hydrolastic Suspension Service unit, is required. Such units are generally available for hire, together with suitable suspension fluid, from most tool hire shops.
In most cases, instructions for operating the unit are supplied with it and are normally printed on the top of the unit.
These instructions should be read through carefully before attempting to use the unit, and followed accurately throughout the operation.
The unit consists basically of a vacuum pump, a pressure pump and a fluid reservoir. Before using the unit, check the fluid level in the pressure/vacuum tank and top up with fluid if necessary. The vacuum and pressure valves are normally identified by colour; YELLOW for vacuum, and BLACK for pressure .
The Hydrolastic system pressure valves are located at the rear of the car on the sub-frame crossmember .
Remember that the ride height of the car will drop as the Hydrolastic system is depressurised, so be careful when working at the rear of the car.
It should be noted that, with the Hydrolastic system in the depressurised state, the suspension arms will contact the bump rubbers at both front and rear, but the car can still be driven with complete safety at speeds up to 30 mph (50 kph) over metalled roads.
When any part of the Hydrolastic system has been disconnected, or after fitting new displacer units or interconnecting pipes, it is essential that the air is evacuated from the system and a partial vacuum created before the system is pressurised.
Once evacuated, the system should be pressurised with the car resting on all four wheels in an unladen condition and with a maximum of 4 galls (18.2 litres) of petrol in the tank.
If a new displacer unit has been fitted, pressurise the system initially to 400 psi (28 kg/sq.cm), or 350 psi (24.5 kg/sq.cm) on early models - see Technical Data for details of specific models application. The system should be left in this over-pressurised condition for about 30 minutes to allow the vehicle to settle, then the pressure reduced to its normal specified setting.
Checking/Adjusting the System Pressure The system pressure is checked using the Suspension Service Unit mentioned above. The car must be resting on all four wheels with a load as described above for pressurising.
The pressure tank on the unit should be pumped up to the system specified working pressure before opening the connector valve, which will already have been connected to the system pressure valve. If a different pressure reading is now indicated, the system pressure should be adjusted by operating the pressure pump to raise the pressure, or opening the pressure valve on the unit to lower the pressure, until the specified figure is obtained.
Checking the Vehicle Ride Height The car ride height is governed by the Hydrolastic system pressure and should be checked with the car resting on level ground and a load condition as described above for pressurising the system.
Measure the height from the axle centre-line to the underside of the wing opening at both the front and rear of the car and compare with the specified trim heights given in Technical Data at the end of this section . If the dimensions are outside the specified limits, the system pressures should be checked and adjusted if necessary to obtain the correct ride height.
The system pressures can be adjusted slightly from the specified figures to obtain the specified trim heights, but large variations will indicate wear or damage to the suspension components or body shell.