Prop Shaft leak 1978 Mercury 90 ss# 5031148

stevehendo34

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1978 Mercury 90 ss# 5031148
Slow leak from bottom of overdrive/prop shaft.
There is a 1 2/3 42mm diameter oil seal on shaft under the big prop washer.

nut-->nut lock washer-->prop-->big prop washer-->seal with rubber-->pressed in seal on shaft.

It just slides of shaft after big washer.
Is this right or should it also be pressed into the shaft?

Seal seams to have cracked rubber.
How can I get a part # and order one?
 

Texasmark

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The lower unit is full of oil. The environment is full of water, maybe salt water. You need to keep the two separated. On that shaft PRESSED into the housing are 2 seals, back to back....one seals from the inside and the other from the outside. You want nice pliable rubber to make a good seal. You can fish them out after you drain the lower unit oil which probably needs changing anyway, if you are the least bit mechanically inclined. Just don't tear up the casting or score the prop shaft. If iboats doesn't have them go online and look for Merc. parts. When finished WM has the lower unit oil in the quart with adapter hose and fitting, in the sporting goods section. Engine vertical, since the drain plug is already out, above the antiventilation plate, on the right side of the engine is a SS screw about the size of a dime which is the vent screw.

Insert the oil fitting in the drain hole and pump till oil comes out the vent. Insert the vent screw. Pull out the adapter and install the drain plug rapidly minimizing the amount of oil that is normally lost in the process.
 

stevehendo34

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" On that shaft PRESSED into the housing are 2 seals, back to back....one seals from the inside and the other from the outside."
The outside seal is not pressed in it just sets on the shaft.
Could the outside seal have worked it's way out of the housing and the inside one pushed it out because it also worked it's way out.
Also I can't tell you how it was when I got it when it was used.
I suppose I could try a socket and hammer to move the inside seal a bit further into the housing then try to do the same to get the outside one back into the housing.

This is really weird if both seals were to be pressed in like you say, because it almost looks like it was assembled wrong then.
Do you this is specific to middle 70s tower of powers.
 

stevehendo34

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"Could the outside seal have worked it's way out of the housing and the inside one pushed it out because it also worked it's way out"
​Exactly what happened will test in water and replace the seals if necessary.
May check with 10 PSI on plug hole to see if pressure holds.
I hope the rubber goes in first on the outer seal when pressing it in the housing?

​I suppose one can get washers for fill and drain screws at auto parts store or hardware store or should I go to dealer.
 

Texasmark

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"Could the outside seal have worked it's way out of the housing and the inside one pushed it out because it also worked it's way out"
​Exactly what happened will test in water and replace the seals if necessary.
May check with 10 PSI on plug hole to see if pressure holds.
I hope the rubber goes in first on the outer seal when pressing it in the housing?

​I suppose one can get washers for fill and drain screws at auto parts store or hardware store or should I go to dealer.

Dealer on the screws and gaskets. Glad you said that. Shows you know something about what you are doing.

From the outside you have metal with minimal rubber showing. For the inside, this side is against the oil. That puts the lips of the seal opposite to each other to seal in both directions as I said.

The gaskets aren't pressed in, rather tapped in. Gasket is flush with adjacent casting when properly installed. If bulging, something had to push them out. Only thing I can think of is pressure in the crank case....from where? Don't think inner alone would push outer out. Something had to push on the inner.

If you test with 10 psig, you might just blow them out....makes exchanging easy. If they fit sloppy, glue them in with JB Weld or Permatex #1.
 

stevehendo34

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Guess I am kidda a dope here, because I don't no what you mean by lips.
There are oil springs on one side of the seals.
Can you just tell me which way the side with the springs goes on the shaft on inner and outer seal.
Thanks!!!!!!!!

Reason, I guess who ever replaced them last put the inside one in backwards, because with the outside one removed only very little rubber shows. I ordered some new ones on iboats and will post a picture on the internet to show how I think they should go
 
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Texasmark

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You can tell in the diagram. The inner part of the seal, where you can see the spring, is facing the same part of the other seal. The smallest dimension of the rubber is toward the other seal which is also positioned with the smallest diameter toward the other seal. You can clearly see the inner seal, on the right, has it's metallic back to you and the one on the left has it away from you.
 

stevehendo34

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Thanks I got new ones in from iboats--cheep--will pull them with drill self tapping screws and little slide hammer
 

stevehendo34

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I need to change them and they won't come out. Anyone drill. screw and use a slide hammer. If so what size bit. They are hard as hell will a cobalt bit drill them.
please only answer if you have done this. I also see there is a what looks to be a huge round nut type thing you might be able to take off with punch and hammer. Wish someone could see how the service man says to do this.
 

stevehendo34

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If anyone is interested this what I did

Well this is a type I not type II thing so it supossedly has only one prop seal unlike my digram. I tried to drill holes and pull it out with screws and slide hamer. No luck to hard even for cobalt bit. Then I decided to remoce carier. Pounded on big ring nut with chisel a.d bfh and it came off. Use old prop with steal bar under it used washers under nut and turned the nut to get the carrier out most af the way. Used som heat but I dought I had to.
 
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