1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 184Get this manual
Pinion Gear, Drive Shaft, and Forward Gear 1Hold drive shaft using Drive Shaft Holding Tool (91-56775); remove (and discard) pinion nut2Remove drive shaft, pinion gear, bearing and forward gear 3Replace pinion gear if it is chipped or worn4Replace bearing and race if either are rusted or damaged; or if bearing does not roll freelyTo remove race, refer to "Lower Drive Shaft Bearing Race," following5Replace forward gear if gear teeth or clutch teeth are chipped or worn
6Replace bearing if it is rusted or does not roll freely; use punch and hammer to remove bearing