piston rod extension 25 is provided with a longitudinal bore 26 at the end of which a rupture disc 27 is secured by means of a fixing nut 28 the chamber 29 is filled with a pressurized gas as the cross sectional area of the piston rod 5 and the cross sectional area of the piston rod extension 25 are equal to each other the volume within the chambers 20 and 21 is independent of the axial position of the piston rod 5 with respect to the cylinder 6 the pressurized gas within the chamber 29 exerts a biasing force onto the piston rod extension 25 and the piston rod 5 in upward direction this means that the steering wheel is biased towards the driver body and can be pushed inwards against the biasing force when the valve member 24 has been brought into opening position the pressurized gas within the chamber 29 can be avoided e g one can provide an opening from the chamber 29 to atmosphere in this case no biasing force is acting onto the extension 25 and the piston rod 5 the opening could be made however with a very small cross sectional area so that on inward movement of the piston rod 5 with respect to the cylinder 6 a damping effect is obtained the rupture disc 27 mounted at the lower end of the bore 26 is so designed that with effect from a predetermined pressure difference between the working chamber 21 and the chamber 29 this disc breaks so overcoming the locking effect of the adjusting element this means that under.