Apparatus for stabilising both guide rods (1) of a tractor comprises a preselecting valve (12) and a control valve (13) connected between the power lifter (9), applied by a first pressure source (P1), and both hydraulic cylinders (7) of the side struts (6). The preselected valve (12) has an additional connection for a separate pressure source (P2). The control valve (13) has two connections (14,15) alternately connected to the hydraulic cylinders (7).
