shaped having a first generally horizontal short distal end member 33 a corresponding in cross sectional outline shape to the socket of the receiver 18 for slip fit therein a generally vertical center section member 33 h is rigidly attached to the distal end member 33 a and extends downwardly a selected distance and is pivotally connected to a second distal end member 33 b the opposing end of the second distal end member 33 b is a u shaped portion for pivotally receiving a lower end connecting mount of a hydraulic cylinder 32 a of the hydraulic jack unit 32 the hydraulic jack 32 of the preferred embodiment is electric however it is contemplated that pressured fluid or air from a hydrostatic system or pump respectively could be used to actuate the hydraulic jack moreover it is contemplated that a rack and pinion assembly can be substituted for or used with the hydraulic jack although it is less efficient and more bulky a pin 32 e connects the cylinder 32 a to the opposing end of the second distal end member 33 b of the coupler 33 by alignment and cooperative engagement of holes formed within the distal end member 33 b and cylinder 32 a the distal end of the piston rod of the hydraulic jack unit 32 includes a connecting yoke having a hole therethrough for pivotally connecting to the corresponding aligned yoke holes of the adjusting mechanism unit 34 by a pin 32 d the.