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Lower Unit Oil leak (question on seal kit) - 1976 Mercury 7.5 HP (SN/4400192)

J

jaywalk101

New member
Hey guys,

I wanted to see if anyone could help me out. I went to drain the lower unit oil for winter storage and found that no gear oil came out at all (bone dry). I'm assuming I have a pretty bad leak. I've drained my lower unit oil in the past and have found water in the lower unit as well. Last year I also took off the gear case and replaced the impeller. Motor seemed to run OK last summer. Anyways.. I want to get a lower unit seal kit for this thing but can't find an all in one kit. I found the parts list (http://www.marineengine.com/parts/m...ru-4851692-usa/gear-housing-assembly-complete) but I'm not sure exactly what I need. Could someone give me some recommendations? The only thing I have on hand is spare drain plug seals. By the way, when I took apart the lower unit last year, it was pretty gunky in there. I'm not very mechanical but i'd like to try some simple stuff to get this motor running good this year. Thanks in advance!!!

David
 
I'm 99 % sure it's the seal just under the impeller. And the shaft in that area is rusty, which means a new seal won' correct the problem.

Jeff
 
kimcrwbr1 said:
Just thinking about it if you let it freeze with water in it you very likely have a cracked gearbox do a quick pressure soap test. Put no more than 8psi pressure in it and spray soapy water all over it and the seals will show you where it is leaking!
Click to expand...

Thanks for your response! I'm now also wondering if it's worth trying to fix. It sounds like I might just be using my electric trolling motor this year.. :(

Now when you say do a pressure soap test? How do I go about doing this and applying 8psi pressure in it? What kind of tools do I need? Thanks again!
 
fastjeff said:
I'm 99 % sure it's the seal just under the impeller. And the shaft in that area is rusty, which means a new seal won' correct the problem.

Jeff
Click to expand...

Thanks for your response fastjeff. With this being said, what options do I have? Am I better off just parting this motor out? Thanks!
 
Try this:

1. Drop the lower unit and remove the impeller.
2. Using two screw drivers, lever the WP housing up and out. (Be careful not to loose any shims.)
3. Knock the seal out of the bottom of the WP housing with a long, thin screw driver. Then buy a new seal (from this site) and an impeller--good time to change it.
4. Take a piece of scrap plastic about 1/16 " thick and cut out a 'washer' that's OD and ID match the seal. (Drill the ID first.) This will be a spacer to make the new seal ride in a different (and better) location.
5. Insert the plastic washer, then the seal and reassemble everything.

Jeff

PS: These LUs are a dog to reassemble, so do it with the motor upside down--and if you can't get it back together, STOP and repost.
 
Thanks for the steps fastjeff! Sorry for the late response. We just recently had our first baby, and I'm now getting a chance to look at the motor again. Anyways.. I have another question. I went ahead and simply put some lower unit oil back in the lower unit. I went ahead and did the bucket test and everything seems to be working OK. Engine sounds good, I'm able to shift, and the prop is turning good when I give it gas. Had it running for about 5 minutes. If I had a cracked gearbox, what kind of symptoms would I be having? I'm thinking about just taking this out in the water and just trying it out. Won't go too far though.. LOL Then drain the oil again and see what happens.....
 
First of all, congrats Papa!

..."If I had a cracked gearbox, what kind of symptoms would I be having?"

Lots of noise and a sudden end in forward motion! I've worked on a ton of those and, if you don't keep the LU in the water, and keep an eye out for water inside (or no oil), they will keep on going.

Jeff

PS: Congrats on getting the LU back on as well! Not an easy job with 'Slanters'.
 
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