At our department we deal with continuous tuning of torsiona l oscillating mechanical systems during their operation, mainly in terms of torsional oscillation size, whereby we use the methods and means of technical diagnostics. One of the manners of continuous tuning realization is the application of the extremal control – experimental optimization. The main advantage of this is that we need not know the mathematical model of the mechanical system. Actuating variable in this regulation is the pressure of gaseous medium in the pneumatic flexible shaft coupling – pneumatic torsional oscillation tuner. By changing the pressure of the gaseous medium in pneumatic flexible elements of the coupling we change its torsional stiffness and thereby dynamic properties of the mechanical system too. The objective of this paper is to present partial results of extremal control operation on the newly built mobile torsional oscillating mechanical system.