Merc 700 driveshaft

[OLLIE45]

Hi Guys,
First post on here so here goes.....
I got a 1979 Merc 700 that runs in saltwater and I can't get the lower unit to drop no matter what I try. I have been through the forum for advice and I know that I have got all the bolts and nuts undone so I'm thinking that it is probably going to be the driveshaft corroded into the crank.
Does anybody know if this motor has a stainless driveshaft or is it carbon steel?
Also, if cutting a hole in the side of the leg so I can get some heat and penetrating oil on to the joint is the answer, can someone give me some dimensions as to where the best place is going to be to cut the hole.

Thanks for any help.

 

[erie_guy]

Re: Merc 700 driveshaft

Ollie,

You may still have a bolt holding the leg from dropping. Check the trim tab area for a bolt that requires a hex wrench to loosen.

I don't have a 70 hp, but service my son's 1974 85 hp four cylinder Merc. I remember a nut on the front of the housing as well, but that I believe was on a Alpha I/O.

Some times it takes a bit of shaking, pulling and wedging to get it loose. Don't give up and cut the housing - that may not solve the problem and you will then have to fix that as well.

We droped his lower unit last month to replace the water pump impeller. It was in bad shape but still had a tattle-tale water flow. Not sure how many years old it was but it was brittle.

erie_guy
Port Clinton, OH

 

[Faztbullet]

Re: Merc 700 driveshaft

If it is still flush with housing ,double check that all bolts are removed and if still flush the sud have grown to DS housing. If this is the case soak the studs in a good penetrating lube and walk it off with alum wedge above studs. If it will drop 1/16-1/4 inch take a old prop and bend the heck out of a blade and run it at the ramp, the vibration will make unit fall off...

 

[erie_guy]

Re: Merc 700 driveshaft

Just make sure the water isn't too deep - or that you have
SCUBA gear to recover it. Keep the trailer straps on the boat to keep it from leaving before you do.

erie_guy

 

[ajgraz]

Re: Merc 700 driveshaft

Ollie,

You may still have a bolt holding the leg from dropping. Check the trim tab area for a bolt that requires a hex wrench to loosen.

Indeed there is a nut under the anode. Did you get that one?

 

[OLLIE45]

Re: Merc 700 driveshaft

Yep afraid so, I got every darn bolt and nut out.
At least I can see a gap between the castings if I hammer a wedge in there now. Only about 1/8" though.

 

[Mi duckdown]

Re: Merc 700 driveshaft

Does the shift shaft come into play on that model? I don't have any of my manuals handy, and it's been awhile since I worked on that year and size.???

 

[Moody Blue]

Re: Merc 700 driveshaft

Does the shift shaft come into play on that model? I don't have any of my manuals handy, and it's been awhile since I worked on that year and size.???

No. Shift shaft and driveshaft are sliding splined joints. If all fasteners are removed, the lower unit would ideally just drop out. Corrosion however tends to make life difficult

 

[chum1]

Re: Merc 700 driveshaft

If it is still flush with housing ,double check that all bolts are removed and if still flush the sud have grown to DS housing. If this is the case soak the studs in a good penetrating lube and walk it off with alum wedge above studs. If it will drop 1/16-1/4 inch take a old prop and bend the heck out of a blade and run it at the ramp, the vibration will make unit fall off...

Wow never heard or thought of that one, learn something new every day. PS i have a prop that you can use but it might shake the powerhead loose too.

 

[turtles11756]

Re: Merc 700 driveshaft

I just won an epic battle with an old Mark 75A . wedges , sledge hammer, crowbar .the front stud had a whitish corrosion and would not let the LU drop. last resort was to torch ( heat ) the bolt HOT and the corrosion gave up after thirty years of sitting .a fresh water only motor .I'd bet it's the shift shaft on yours