A multi-disc brake assembly with cooling system, comprising: a housing (7a, 7b); a coupling shaft capable of rotation with respect to the housing and comprising an axial torque transfer feature on the outside surface; a first axial fluid rail formed in the shaft and comprising an opening adjacent an end of the shaft; and a first plurality of orifices fluidly connecting the first axial fluid rail to the outside surface of the shaft; at least two rotating braking discs with centre holes slidably mounted along the torque transfer feature on the shaft; a plurality of stationary braking discs with centre holes mounted to the housing and interleaved among the rotating braking discs such that the stationary braking discs are incapable of rotation yet capable of axial motion with respect to the housing (7a, 7b) and such that a stationary braking disc is located on each side of a rotating braking disc; a plurality of friction materials located in each interface between the rotating braking discs and the stationary braking discs and mounted to either the rotating braking discs or to the stationary braking discs; a plurality of gaps between the outside surface of the shaft and the plurality of friction materials and between the interleaved rotating braking discs and the stationary braking discs, wherein the first plurality of orifices are located adjacent to the gaps; whereby a disc pack is created comprising the at least two rotating braking discs, the plurality of the stationary braking discs, and the plurality of friction materials; a clamping mechanism for clamping the rotating braking discs, the plurality of friction materials, and the stationary braking discs together; a supply of coolant fluid connected to the axial rail opening in the shaft; and a mechanism for delivering the coolant fluid from the supply to the first axial fluid rail; characterized in that the first plurality of orifices in the first axial fluid rail essentially decrease in size from the middle of the disc pack to the ends of the disc pack. a housing (7a, 7b); a coupling shaft capable of rotation with respect to the housing and comprising an axial torque transfer feature on the outside surface; a first axial fluid rail formed in the shaft and comprising an opening adjacent an end of the shaft; and a first plurality of orifices fluidly connecting the first axial fluid rail to the outside surface of the shaft; at least two rotating braking discs with centre holes slidably mounted along the torque transfer feature on the shaft; a plurality of stationary braking discs with centre holes mounted to the housing and interleaved among the rotating braking discs such that the stationary braking discs are incapable of rotation yet capable of axial motion with respect to the housing (7a, 7b) and such that a stationary braking disc is located on each side of a rotating braking disc; a plurality of friction materials located in each interface between the rotating braking discs and the stationary braking discs and mounted to either the rotating braking discs or to the stationary braking discs; a plurality of gaps between the outside surface of the shaft and the plurality of friction materials and between the interleaved rotating braking discs and the stationary braking discs, wherein the first plurality of orifices are located adjacent to the gaps; whereby a disc pack is created comprising the at least two rotating braking discs, the plurality of the stationary braking discs, and the plurality of friction materials; a clamping mechanism for clamping the rotating braking discs, the plurality of friction materials, and the stationary braking discs together; a supply of coolant fluid connected to the axial rail opening in the shaft; and a mechanism for delivering the coolant fluid from the supply to the first axial fluid rail; characterized in that the first plurality of orifices in the first axial fluid rail essentially decrease in size from the middle of the disc pack to the ends of the disc pack.