Allison MH20R

[Sadey]

The shaft coupler on my starboard motor has developed a serious leak. Based on the spray pattern it’s the coupler not the real seal. It’s about $4000 to replace the coupler with no guarantee it will stop the leak. This from a highly recommended mechanic. The splines on the output shaft of the transmission could be worn enough that a new coupler will still have enough slop to leak. So we’re looking at replacing the transmission. Obviously this seems like a radical solution, but considering the logistics and cost involve, it might end up being the best solution. Obviously the leak has to be fixed because, 1 it’s making a mess 2, It’s the right thing to do and 3 it’s going to come up on a survey at some point. Curious if anybody else has gone down this path and if so, what was your solution?

 

[Avenger]

Not on transmissions, but it happens on vibration dampers sometimes, where oil will creep through the bore of the damper where it goes on the crankshaft.

Usually applying sealant to the washer under the damper bolt will keep oil from escaping.

 

[rsmith]

The coupler and output shaft need to be clean and anaerobic sealant to be applied before reassembly. How do you know it’s leaking through the splines? Is it coming out the mating flange ?

 

[drewread]

The shaft coupler on my starboard motor has developed a serious leak. Based on the spray pattern it’s the coupler not the real seal. It’s about $4000 to replace the coupler with no guarantee it will stop the leak. This from a highly recommended mechanic. The splines on the output shaft of the transmission could be worn enough that a new coupler will still have enough slop to leak. So we’re looking at replacing the transmission. Obviously this seems like a radical solution, but considering the logistics and cost involve, it might end up being the best solution. Obviously the leak has to be fixed because, 1 it’s making a mess 2, It’s the right thing to do and 3 it’s going to come up on a survey at some point. Curious if anybody else has gone down this path and if so, what was your solution?

Do you have some photos you can share of the situation?

 

[Briankinley2004]

Can't you just replace the output shaft instead of the entire transmission?

https://dieselpro.com/allison-marine-transmission/allison-mh/shafts-ejes.html

 

[Sadey]

Still working the possibilities, these suggestions help. The leak started out as “clean oil” the turned to a rust color.

 

[Captain Ralph]

Can't you just replace the output shaft instead of the entire transmission?

https://dieselpro.com/allison-marine-transmission/allison-mh/shafts-ejes.html

That would still require R&R of the whole clutch assembly.
Then major tear down of the clutch that may has well go thru a rebuild or exchange.

 

[Captain Ralph]

Still working the possibilities, these suggestions help. The leak started out as “clean oil” the turned to a rust color.

Your picture shows it perfectly.
Output flange/shaft O ring oil leak.
Flange/shaft nut is probably loose.

If you have room to push the shaft back several inches and have an air tool with socket, that job is correctly doable on board.
Remember to drain all the oil out first.
Order the O D seal and the O ring.
Heavy grease the O ring.
And of course, RTV under the flange/shaft nut.

The tech that wanted to replace the whole clutch probably expects metal in the clutch from the wear between the flange & shaft. This will happen if not already. Oil lab report can help here.

Replacing the flange is pending a close inspection of all wear surfaces. If it is still true, should be re-usable. Have a credit card ready just in case. ☺

I would consider this an emergency repair this winter. No more water skiing until it is fixed.

 

[rsmith]

They used to have parts breakdown on the site but it looks like there’s no link. Highly unlikely the splines are worn even with a loose nut. Many times mechanics just goober up the nut and washer with RTV that deteriorates over time. Plus the surfaces need to be free of oil film. I douche everything down with brake cleaner. The not approved in California good stuff. Don’t use carb cleaner it leaves a film and eats plastic and rubber.


https://www.acadianmarinetransmission.com/

 

[drewread]

They used to have parts breakdown on the site but it looks like there’s no link. Highly unlikely the splines are worn even with a loose nut. Many times mechanics just goober up the nut and washer with RTV that deteriorates over time. Plus the surfaces need to be free of oil film. I douche everything down with brake cleaner. The not approved in California good stuff. Don’t use carb cleaner it leaves a film and eats plastic and rubber. https://www.acadianmarinetransmission.com/

This site has a parts diagram. No clue about it this company x but there is a parts diagram. https://www.valliantindustriesinc.com/allison-marine-transmission

 

[rsmith]

This site has a parts diagram. No clue about it this company x but there is a parts diagram. https://www.valliantindustriesinc.com/allison-marine-transmission

That’s the M gear the MH has 2 oil seals on the output shaft. But the basics are the same you can see the nut there it’s Like a 4 wheel drive hub removal socket

 

[Sadey]

Pulled the coupler yesterday and lots of oil came out when the coupler and shaft started to separate. Also, it was obvious the shaft wasn’t aligned correctly. The output shaft was loose indicating the internal bearings are worn. Looks like a rebuilt transmission is in the very near future. Acadian Marine has one in stock so now it’s just a logistical issue at this point. Something good came from this, I didn’t know about the screen that needed cleaning at each oil change interval. Removing and replacing the oil through the screen housing is so much easier.