Re: Help with 1969 Chrysler 70hp Lower Unit
You need to replace all the seals. Prop shaft, drive shaft (under the water pump), shift rod seal, and gaskets on the fill and drain plugs. The shaft seals are standard and can be bought at a bearing supply house. The shift rod seal was used on all engines up until about 1994 so order one at the Mercury dealer or right here at iboats.
The lower unit takes about 30 ounces of lubricant and it is important to be certain it is full so the top bearing is not starved.
NOW: when water gets into a lower unit, residual oil has additives that tie up free oxygen and in most cases, if the unit is not open, no rust will occur. HOWEVER: once you drain it, air gets in and rust can start. SO, it is best if you flush out the lower unit with solvent of some sort then squirt in a light oil until you can re-seal and re-fill it. If you are replacing the seals, might as well disassemble it and clean the gears. That is a two piece lower unit. There are seals under the washers on the top bolts, an O ring at the bottom of the long front stud, and a large O ring at the perimeter of the gearcase torpedo. Any of these areas could also be leaking. The rear gland held with two allen head screws is sealed to the case with an O ring but usually does not leak.
