I notice that you said "RR MGF and I a TF but both 15's", so you can compare the ride comfort of your (Or is it RR's?) F ride "softness" with the TF. Unless the TF is a very late model or was specified with or retrofitted with the Softride Option, you SHOULD find that the F is much softer than the TF. If NOT, then the GAS part of your hydragas units has lost some or all of it's gas, which of course provides (almost) the only spring. I read somewhere that the original Dunlop-specified design life of Hydragas units was 10 years, so all as-built F's have units at least 21 years old. I suspect that whenever a unit is depressurised, gas tends to diffuse through the rubber diaphragm, dissolve in any remaining low-pressure fluid, and/or just get lost to the atmosphere. Clearly, any serious rusting of the hydragas units is likely to give porosity in the steel and even faster loss of gas.
There must be some ex Dunlop or Rover suspension design team guys out there how understand this stuff much better than me, and Hydragas and Hydralastic Service limited (
enquiries@hahsltd.co.uk) seem to have a good reputation, though I appreciate that they are a long way from you in the Borders.
Anyway, good luck with experiments with Tyre pressures etc. and thanks for raising the warning , which has resulted in very useful info. regarding tyre hardness and the need for caution with cold tyres.
