Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 255Get this manual
7 Lightly rotate the drive shaft clockwise and counterclockwise to measure backlashThe dial indicator should register .030 in(0.76mm) to .050 in(1.27mm)Take four readings rotating the drive shaft 180 degrees each timeIf the backlash is not within specifications, then gear case is not properly assembled or components within the gear case are excessively worn and should be replacedPosition shim against shoulder in gear case
Forward Gear
DETERMINING FORWARD GEAR BACKLASH 1Install load washer (12-37429) over small V-6 or 70- 11 RH standard propshaft(44-941480r44-12238) so that ltseats against the REAR shoulder of the spline teeth
aShoulder Shim