Most car suspensions are based on a spring - used to be flat cart type but now most cars have coil springs.
Some cars did go with a hydraulic suspension - early minis come to mind.
If you really mean the shock absorber, or damper, then they can be pressurized and tend to use oil.
Never seen a vacuum based system on trucks or cars but it might have been done - however, given how complicated it would be...
Edit: based on the addition, some things use high pressure nitrogen cylinders, or bags, to provide a spring-loaed action for hydraulic systems. One example is for hydraulic arms that need to move if they encounter an object but need to stay put otherwise. Some are over 400Bar so knowing what you are about to undo is crucial...