In this system a displacer unit is fitted at each of the four wheels. The displacer units are all interconnected by means of fluid. In the displacer unit, rubber (under compression and shear) is used as a spring whereas fluid under pressure acts as a damping medium. The stem is connected to the wheel through suitable linkage so that its movement is proportional to the up and down movement of the wheel. A two way valve assembly controls the up and down flow of the fluid. The upper valve opens up when the fluid pressure below rises sufficiently. Similarly the lower valve allows the fluid to pass in the downward direction under pressure. The two valves are assembled at right angles to each other.

When the Piston moves up due to the movement of the wheel, the diaphragm pushes the fluid up through the opening, by pushing the damper valve. The fluid under pressure above the valves, then compresses the rubber which acts as a spring. The wheel bounce, the body roll and the pitching are controlled as explained below.

Bounce and roll :- If both displacer units are deflected simultaneously as in pure bounce or roll, no interflow occurs. So the fluid pressure is conveyed entirely to the springs, which deflects simultaneously, giving an increased suspension rate. Since a condition of pure bounce is rearly experienced, the full effect of two springs together is normally felt only during roll, when the outer wheel deflect together.

Pitch :- In the case of pitch when a front displacer unit of the hydrolastic system is deflected by upward movement of the road wheel, fluid is impelled through the conduit to the displacer which raises the rear end of the car and thus reduces the angular acceleration. As a result, pitch is virtually eliminated and the car maintains a substantially level attitude. Similar action takes place when the rear wheel moves up.