A system and method for operating a large single engine sweeper includes a two-mode transfer case assembly inserted into the chassis drive train of the vehicle on which a package of sweeping equipment is mounted. In road mode operation, power from the chassis engine passes through a chassis automatic transmission, through a two-mode transfer case assembly to the differential and real wheel assembly. In sweep mode, power passes from a propel hydraulic motor into the two-mode transfer case assembly and then to the differential and real wheel assembly.