an improved suspension assembly for a high capacity hauling vehicle having a strut that is connected to a two - chamber cylinder or accumulator . the strut has a first section that is connected to the axle and a second section which is secured to the vehicle chassis and telescopes in relation to the first section . further , the strut has a chamber that contains a gas and a liquid . the suspension assembly accumulator has two chambers that are separated by a movable piston . the first accumulator chamber is filled with liquid while the second accumulator chamber is filled with a gas . the gas - filled accumulator chamber is connected to the strut chamber , which also contains gas , by way of a hose which includes a fixed size orifice . the orifice is sized to regulate the flow of gas between the chambers so that the dynamic stiffness characteristic of the strut varies as a function of the speed of the movement of the axle relative to the vehicle . the liquid filled accumulator chamber is connected to a source of liquid under pressure so that the volume of liquid in the accumulator may be varied . a self - leveling feature senses the relationship of the axle to the vehicle to automatically level the vehicle . the operator of the vehicle may manually override this feature to raise or lower the vehicle body upon command .