1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 264Get this manual
NON BIGFOOT GEAR HOUSING
FORWARD GEAR 1Inspect forward gear teeth for breakage, rust, chipping and excessive wear2Inspect forward gear clutch jaws for wearRounded jaws indicate the following: Improper shift cable adjustment or linkageEngine idle speed too highShifting too slowly
a-Gear Teeth b-Clutch Teeth 3Inspect propeller shaft FORWARD gear bushing surface to determine condition of bushingIf surface is discolored (from lack of lubricant), pitted or worn, propeller shaft and bushing should be replaced