On my BX there is a knob that locks the MMM to the top or adjust how high the cut,, there is another knob in the same general location by the floor that controls the speed the 3 point hitch arms come down and if the Knob/valve is completely closed the lift arms will stay in the up position. open this valve and the arms should come down, open it all the way and they will come down fast..
Hope this helps and fixes your issues..