1989 Mercury outboard lower unit rebuild

[dmiles452]

I am getting ready to replace the seals and gaskets on my 100 hp 4 cylinder outboard lower unit. What seals should I suspect is leaking water into the gear case? I will replace the water pump while I have the unit apart. I have done the water pump 4 times in the past, but I wonder if I should leave the seals and gaskets to a pro.

 

[Chris1956]

Use the gear pump tube as a hose to pressurize the gearcase. A bicycle pump will provide enough pressure. See where it is leaking.

My '77 Merc leaked at the waterpump base seal, several times. Easily replaced. My '93 Merc has leaked twice at the shift seal. You need a spanner to replace it, but still easy repair.

None have leaked at the propshaft seal, which is really good news.