Hydragas displacers have two chambers, the lower chamber being full of fluid and a valve provided for a suspension pump to be attached and the ride height of the vehicle maintained. The top chamber is pressurised with Nitrogen Gas and no provision was made to top this up as the manufacturers estimated that the charge of gas would last the life of the car which was estimated at 15 years. The gas gradually escapes from the units over decades, this is perfectly normal, this escape would have started as soon as the unit was manufactured and very slowly progressed. The problem is that all Hydragas units are now older than their design life and this loss of gas causes a hard and uncomfortable ride but not many people know that this also causes the top gas separator diaphragm to be higher in the unit than it should be, this causes the diaphragm to be in contact with the top of the unit every time the car hits a bump. The top of the unit has a riveted plug where the unit was charged with gas during manufacture and this leaves sharp edges inside the top of the unit where contact with the diaphragm eventually leads to it being holed and destroying the unit. The units don't generally deteriorate with age as such so if the units are re-gased as soon as a harsh ride is felt it prevents the diaphragm from ever getting damaged so the units have the potential to last indefinitely. Many perfectly good units are ruined just because they are low on gas and the car has been used for too long in this condition, all this can be avoided with a re-gas and this brings the ride back to how it was when the car was new, lovely and comfortable with superb cornering, it's a long term fix and provided the units don't fail for any other reason, and this is rare, another re-gas wouldn't be needed for another 15 - 20 years.
As Featured in Practical Classics
and Autocar Magazine