# Replacing Prop shaft seal?



## Carpn (Apr 5, 2004)

Drained my lower unit this weekend and found a little bit of water in the gearcase. I'm assuming that I need to replace the prop shaft seal. I have the O&M book for my outboard but I think it makes it sound harder than it really is. Is this something I can replace myself or would it be advisable to take it into a marina....It sounded like there may be a couple special tool needed to make the job alot easier.....The motor is a 2000 Johnson 150.....
Thanks for the input fellas.


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## Workdog (Jan 10, 2007)

That leak could be coming from a couple other places too. Are the seals good on your drain plugs? I had a leaker once from a bad seal at the water impeller. A leak test will confirm where it's coming from. Not familiar with your motor, but I think you need to pull the prop shaft in a Merc.


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## Carpn (Apr 5, 2004)

Thanks, I forgot about the impellar seal....I've had the motor long enough I probably should take it in and just have all the seals replaced to be on the safe side.


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## KaGee (Sep 8, 2006)

Before you pull it apart, or spend needless money, do a pressure check. As Workdog said, a lot of leaks happen at the vent and drain screws. Those nylon seals should be replaced every season when you change the oil. 

If you do have another seal leaking in the lower unit, I recommend a complete re-seal of the lower unit.


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## Carpn (Apr 5, 2004)

OK....Do I need to take in somewhere to pressure check it or can that be done at home.


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## KaGee (Sep 8, 2006)

You can do it at home... if you are handy.
Here it is...









This tool for pressure testing that can be put together from parts available at most car parts stores.

They are 1) vacuum & fuel pressure gauge with 3 way tee. 
2) Hand bicycle air pump (for 8 to 12 p.s.i. max). 
3) Oil fill screw 3/8 inch robbed from a boat lower unit oil pump/refill kit.

You can get fancier with one of those hand-held MightyVacs and a true professional would not only do a pressure check, he would also pull a vacuum check.

Drain the oil in the lower unit.
Replace the vent screw and tighten down.
Insert the 3/8ths fitting into the drain. Tighten down using the nylon washer. I also use an O-ring to make a good seal.
Pump up pressure, not to exceed 12lbs.
Let stand for a two-three hours.
Any loss of pressure (provided the vent and drain is sealed properly) indicates a seal is bad. 

To me it irrelevant at that point which seal is bad, the unit should have them all replaced. The only exception to that would be if you tore up a seal with fishing line on the prop shaft. I would just replace the prop shaft seals at that point.


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## Carpn (Apr 5, 2004)

Thanks, I have a vacumn/pressure pump here at work and all the other fittings and stuff. So is the darin/ nent hole threads 3/8 npt. I have a buncha 3/8 and 1/4" stuff that I could rig up a T with a vacumn pressure gauge and use teflon tape on the threads.
I appreciate all the help guys.


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## KaGee (Sep 8, 2006)

Your drain and vent are NOT NPT. 3/8ths-16 I do believe.
Rob the fitting from one of these...


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## Carpn (Apr 5, 2004)

Thanks...I have one of those plunger pumps at home.....


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## ezbite (May 25, 2006)

good info, ive never done a pressure test of my lower unit, i will be doing one now.


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## Carpn (Apr 5, 2004)

Well, I tested it and it bled off pretty quick. i checked all my connections and the vent and drain plugs with soapy water and didn't see any bubbles. I then pulled the prop off and there was some braided line wrapped around the shaft in front of the thrust bearing...Looks like it had worked its way into the seal. Not the news I wanted but at least I know what it is.
Whats a realistic price to have all the seals redone on a lower unit? I looked at my O&M manual and I'm not sure I wanna try and redoe them all myself.


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## KaGee (Sep 8, 2006)

Sorry to hear that man.
Not familiar with your market.
Maybe a new post in the Lounge asking for recommendations?


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## KaGee (Sep 8, 2006)

They'll probably suggest it, but since it will be apart, have them replace the water pump impeller.


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## Carpn (Apr 5, 2004)

I'll probably just have them do it. I replace it myself every other yr but as long as they are in there they might as well do it. Thanks again for all your help. I don't think I'm the only one thats gonna benefit from your advice.


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