which reference is made the words 34 inwardly 34 and 34 outwardly 34 will refer to directions towards and away from respectively the geometric center of the device and designated parts thereof the above applies to the words above specifically mentioned derivatives thereof and words of similar import the present invention relates to a pneumatically operated actuator of the mechanical push pull rod type which is suitable for an automatic or semi automatic vehicular master clutch actuation system a portion of a typical push rod mechanical clutch operation linkage 20 is illustrated in fig3 rod 7 is engageable with clutch release lever 22 which is pivotably fixed about pivot point 26 with the clutch release bearing 24 a return spring 28 is provided to bias the lever 22 and bearing 24 into the clutch engaged positions thereof the operating rod 7 of the invention is moved axially in any known manner by pneumatic power applied to a primary piston in a cylinder in some arrangement such as automatic or semi automatic actuation where the degree of engagement of the clutch needs to be reliable and repeatably sensed thus the primary piston should maintain its relative position with respect to the operating stroke of the clutch whatever the degree of mechanical wear in the clutch or in the clutch friction surfaces if a computer type control electronic control unit 34 ecu 34 does not 34 know 34 when a clutch is just beginning to bite or is 50 engaged for example operation will be unpredictable rough or lead to over rapid wear of the drive or of the driven device e g the vehicle some types of clutches wear such that the incipient engagement position of the.