76 merc 850 lower unit problems

[angis431]

so last week, i get my boat to the ramp, andnotice oil dripping from my propseals. went home and drained the bullet. the oil was black, but no water. let the unit drain for a day ,put the screw back in and started the motor with the garden hose hooked up. now i have water in the oil.what seals should i replace? prop or the ones on top of the lower unit? total rebuild? if so can it be done in a day or two?

 

[Mi duckdown]

Re: 76 merc 850 lower unit problems

Seals on top, since it was not in the water, and run on muffs. Easy fix.
BUT, is the driveshaft carbon steel? or stainless steel?
Carbon had got grooved at the seal letting water into the lowerend.???
Could be the shiftshaft seal also.
A pressure and vacuum check will tell your what is happening with your lowerend.

 

[angis431]

Re: 76 merc 850 lower unit problems

dont think the shaft is bad. there was some kind ofseal behind the thrust hub, double walled rubbur with a spring inside. it had vibrated loose,so i pulled it out and cleaned the crud out of the spring and put it back in. no more drip.yay. now my bullet is full of what looks like vanilla icecream! how would i do a pressure/vacuum test? funds are low but maybe i can do something

 

[Wingedwheel]

Re: 76 merc 850 lower unit problems

Those prop-shaft seals are about $12 apiece and yes, there are two. I had the same motor and that's where my leak was. You have to pull the LU apart to get to them, but its not that bad of a job if you have the right tools. Just make sure you torque the retaining nut to the correct spec when you re-install the carrier. I think its about 235-250ftlbs but you might check on that or you'll still have water in the oil. if the seal vibrated loose that's not a good sign as those are pressed in.

 

[angis431]

Re: 76 merc 850 lower unit problems

guys thanks for the help. gonna replace every seal in the lower unit and will post with pictures when its done. any idea how long a rebuild will tak? seems like about 90 parts in lower unit. think it can be done in two days?

 

[merc850]

Re: 76 merc 850 lower unit problems

Here's are diagrams of the LU

and this tool takes out the bearing carrier nut

 

[Chris1956]

Re: 76 merc 850 lower unit problems

Angis, Do yourself a favor. First, don't run the motor w/o a gearcase full of marine gearoil. You will only ruin the bearings, gears etc.

Second, replace the waterpump base first, with it's new driveshaft seal, and see if that is where the leak is. It is a heck of a lot easier, and is likely the bad seal. Inspect the driveshaft where the seal rides, to make sure it doesn't tear the seal.

 

[angis431]

Re: 76 merc 850 lower unit problems

hey thanks for the help guys. i removed my lower unit, but my shift shaft stayed mated to the upper unit. now the marine shop says they cant pressure/vacuum check the unit without it. better question is, what can of worms did this open? and chris i would never run the engine without the oil. oils cheap engines arent.

 

[chum1]

Re: 76 merc 850 lower unit problems

can o worms only because the last guy didn't do it right/ didn't know how/ gave up and sold cheap/
The shift shaft has a circlip that prevents it from coming out (corroded away or possibly left out).

There is an article thats posted about how to reinstall shift shaft without pulling all the guts out, might as well change all the seals, if you know what your doing and have the parts and tools a person could be able to change all seals in under an hour.

Chris1956 is probably correct in waterpump seal problem, check to make sure they aren't in backwards.

If everything is changed fresh it should last you many years to come.