Mercury Mariner 30/40 4-Stroke Outboard Service Manual 1998, Page 407Get this manual
NON-BIGFOOT GEAR HOUSING
Gear Housing Reassembly
IMPORTANT: This gear case assembly does not have have any shims for the gear assembliesBacklash cannot be adjustedThe mechanic must verify that all bearing races are firmly seated in the gear case during reassembly and that all gear case components are in serviceable conditionPrior to installing the seal carrier and water pump assembly on the drive shaft, the FORWARD gear should be held stationary (with screw driver or similar tool)While pulling up on the drive shaft, lightly turn the shaft back and forth lightclicking" sound should be heard indicating the presence of backlash between FORWARD and PINION gearsIf this backlash is not present, the pinion gear race andor forward gear race are not fully seatedRaces should be removed and inspected for debrisReinstall races and check backlashIf backlash is still not present, replace gear housing