Abstract: A retractable tag axle assembly, including a hydraulic cylinder for up-and-down reciprocation of the tandem axle, is provided with structure for protecting the cylinder against damage from shock forces imparted to the suspension spring through the ground-engaging wheels. The structure includes a crank secured to one end of the spring and coupled with the hydraulic cylinder at a point intermediate the ends of the spring such that the full length of the latter is available for up-and-down flexure, yet the overall length of the assembly, is not increased over that of conventional tag axle assemblies. Ball-and-socket type mountings between the ends of the cylinder, and the frame and crank respectively, permit canting of the cylinder to avoid the adverse effects of twisting of the crank relative to the frame.