Abstract: A coupling assembly is provided for detachably securing the thills or shafts of a two-shaft racing sulky to the harness saddle which accommodates adjustable lengthwise and vertical positioning of the shaft relative to the saddle while accommodating a limited range of free pivotal movement of the shaft about a point which is fixed relative to the saddle. The assembly provides for precise tracking control of the sulky while affording reasonable freedom for relative motion between shaft and saddle to accommodate twisting and minor linear motion of the saddle by body movements of the horse in stride and turns.