A suspension unit, for example for a track-laying vehicle, comprises an oil-filled cylinder within which a piston, connected to a piston rod, is provided. The cylinder 4 is oil-filled, and communicates with an upper region of a spring chamber, the lower region 46 of which contains gas under pressure. The piston rod has a hollow interior filled with gas under pressure. The piston is connected by a connecting rod to a secondary piston which is slidable within the piston rod. On rebound the piston rod and the piston move relatively to each other between a retracted end position and an extended end position. During this movement and the return movement, oil is transferred, by way of apertures between damping chambers which serve to damp the relative movement of the piston and the piston rod so avoiding shock loading at the end positions of the movement.