A method of operating a drive-train of a vehicle having a drive engine, at least one drive axle and at least one further axle which can be drivingly connected by a pressure-controlled switching device. The switching device is acted upon by an opening pressure to disconnect the axle. When a service brake system of the vehicle is actuated, the axle is automatically connected by actuating the switching device, which is actuated as a function of a braking mode determined during actuation of the brake system, in such manner that when the brake system is actuated in a first braking mode, the switching device is actuated by a first control pressure to transmit a first torque, and if at least one parameter that characterizes the occurrence of a second braking mode is exceeded, the switching device is actuated by a second control pressure to transmit a second, higher torque.