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lower unit pressure test

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iskjohnson

New member
I am new to site and need some help.
I recently purchased a boat with a '88 Yamaha 30 hp motor. There was water in the gear oil. After watching some youtube videos of putting in lower unit seal kits, I decided I would try it. I built a pressure tester and pressure tested the lower unit before I did anything else to test my tester and see where the leaks are. I submerged it when pressure testing with less than 10 lbs pressure. No air leaked from the prop shaft, only a few bubbles from the drive shaft when I turned it, but air is pouring out of the housing right in front of the shift linkage. Is this normal or do I have a cracked housing (from water in it freezing?) or another issue? It is not where I expected to see air coming from.

I have not removed the water pump housing or anything else yet. I appreciate any advice, Thanks.
 
There is normally a seal on the shift shaft as well. Is this what is leaking? Don't forget that you ideally should vacumm test as well. Some of the seals are holding vacuum rather than pressure.
 
It actually looks like it is coming from in front of the shift shaft but I cant tell for sure. I will test it again out of the water and spray some soap on it and I should be able to tell. I don't see anything in the lower unit seal kit that looks like the right size for the shift shaft, is that a separate item?
 
Sorry, I can't tell you for that particular engine, but there is usually some sort of seal around the shift shaft.
 
yup its shift shaft leaking. I pulled it out, looked ok so I put it back in and pressure tested, no leak. Pushed it down to put in forward, no leaks. Pulled it up for reverse, seal popped loose and leaked like crazy. Plastic bumps that expand into casing to hold it look worn and not holding it in there solid. The lower unit seal kit does not have any parts for the shift shaft. Thanks for help aliboy.
 
Nearly all lower units have a prop shaft seal x 2 (vacuum and pressure), a shift shaft seal, and a drive shaft seal x 1 (or 2). Figured it had to be the one you hadn't checked. Good luck with the repair.
 
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