Yamaha Outboard F15A F9.9C, FT9.9D F15 Service Manual, Page 326Get this manual
BACKLASH MEASUREMENT (F15AF9.9C)
8 Attach the backlash indicator onto the drive shaft (12.8 mm in diameter)Backlash indicator: YB-0626590890-06706 Attach the dial gauge onto the lower unit and have the dial gauge plunger contact the mark on the backlash indicatorBase plate: YB-0700390890-07003 Dial gauge set: YU-0309790890-01252 Magneto base: YU-3448190890-06705 Slowly turn the drive shaft clockwise and counterclockwiseWhen the drive shaft stops in each direction, measure the backlash2Adjust: Forward gear backlash Remove or add shim(s)NOTE: