Abstract: An improved mechanism is provided for selectively altering the position of a depressible, outwardly biased, shiftable structure, such as a splined shaft, and for releasably holding such structure in either a depressed or an outwardly shifted position. The mechanism is especially adapted for use with powered wheel hub assemblies, such as commonly employed in combine or normally self-propelled agricultural implements or the like, in which provision is to be made for disengaging the hub from an associated power shaft to permit two-wheel drive or towing of the implement at higher speeds than those used for operation of the implement. The power shaft is disengaged when the plunger of the device is pushed inward and turned through 90.degree. to lock it in position. On releasing the handle by turning through 90.degree., the spring loaded plunger is retracted and the powered wheel hub assembly is engaged in a drive position.