1977-2000 Suzuki DT5/6/8 Outboards Service Manual, Page 85Get this manual
GEAR CASE
sure that there is backlash between reverse .gear and pinion gear, although small amount of backlash there is permissibIeeliminate the backlash, if increase thickness of the shim behind reverse gearmeans of the shim the inner side of forward gear and reverse gear, adjust the thrust play of propeller shaft to this value:
Propeller shaft thrust play