Nope, 4 wheel air suspension was not available on any of the 1992-99 S-class
w140 chassis. In 2000 it became standard on the New S-class series in the US.
Most S420's were not equipped with the $940 optional Automatic rear-axle level
control that consisted of hydropneumatic rear shock absorbers. And never have I
seen S420 with the $2700 Active Dampening System shocks (ADS). I am sure there
is one out there, but it would have been a special order, most wanting those
options opted for the S500 where the level control is standard or the S600
where everything is standard. To know if you have ADS, you will have a selector
switch with a picture of a shock absorber on it, just below Climate control,
and just above the seat heater switches (if you have the option).
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