An elective down pressure system for cutting units (102 - 106) of a grass mowing machine (100) with lift and lower mechanisms connected to the lift arms (107 - 111) with lost motion couplings(142, 143, 195, 197, 198) that may be set to either a downforce position in which the lift and lower mechanisms urge the lift arms (107 - 111) to apply downforce to the cutting units (102 - 106) while thy are on the ground surface, or a no downforce position in which the lift and lower mechanisms discontinue urging the lift arms (107 - 111) to apply downforce once the cutting units (102 - 106) are on the ground surface.
