Hydragas Suspension units – faults and repair

Fixing them sooner rather than later saves you a lot of money!

The hydragas units consist of a sealed rubber bag of nitrogen gas, which provides the springing, and an adjacent chamber filled with liquid, which transmits the mechanical suspension loadings to the gas bag, and also provides the means of connecting front and rear units.  As fitted to the MGF, the system provided a very good combination of ride and handling.  However, there are two conditions which can develop with this suspension as it ages:

  1. The suspension settles gradually over the years.  This is due to the very gradual diffusion of the gas out of its rubber bag – a bit like the way a balloon goes down over time.  This loss of ride height can be rectified for quite some time by pumping more fluid into the fluid chamber, raising the car back up to the correct height.  However, the more gas is lost, the less springing there is and the suspension becomes gradually firmer as time goes on – getting to the stage where it is very hard riding.  The only cure for this is to remove the suspension units and re-fill them with gas.  This requires specialist equipment as the chambers were sealed by the factory.
  2. The suspension ruptures – either the gas bag or the bottom diaphragm of the fluid chamber.  This is a very sudden occurrence which leaves the ruptured side sitting on the bump stops.  Visually, it is a few inches lower than the other side, with the top of the tyres protruding up a bit past the top of the wheel arch of the exterior bodywork.  The only fix for this is to replace the hydragas unit.  This is more problematic as new units are no longer available, so a second hand one must be found – and the condition of these can vary considerably.

Fortunately the rupture scenario is reasonably easy to avoid, as it is brought on by the amount of gas which has been lost from the system.  When too much gas is lost, the pressure needed in the fluid system to raise the car increases substantially – and it is this extra pressure which delivers the fatal blow.  A second cause from the lost gas is via the rivet which was used by the factory to plug the gas injection point when it was made.  If the bottom of the gas balloon (thanks to its reduced volume) makes contact with the rivet the balloon can puncture and the unit is dead.

If the system is re-gassed in time, then both these scenarios are avoided and the life of the units substantially prolonged.  In addition, the excellent original ride qualities are restored.

We are able to service the original units for all of the above situations.  There are also on the market some spring conversion units which do away with the gas bags altogether, but are a couple of thousand dollars worth before GST and fitting – so not a cheap fix.

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