Allison M20 parts schematic

[Hatteras58]

Looking for a parts schematic for an Allison M20 transmission. In particular, I could use a diagram showing seals/gaskets. A link to Acadian that was posted on the HOF several years ago no longer works.
Thanks in advance for any help.

 

[Play'N Hooky Too]

I'm sure you are probably already familiar with boatdiesel.com, but I have found them to be a very valuable resource. They do have a nominal (boat dollar-wise) membership fee, but the access to technical information that it provides is more than worth it, in my opinion.

https://boatdiesel.com/

 

[Captain Ralph]

Are you wanting to rebuild your self? Repair your self? Warranty it your self?
There is a reason these experts are still working so well for so long on these older, out of production products.
Long ago we have learned to let the experts support, sell & rebuild certain products,, this is one of those products that keep meat on their tables and can not keep bologna on mine. Let those who know, do the work and supply the parts.
To many part numbers for the same piece. Just call one up and ask for the part. They will ship it to you. There will be no warranties of course. but you will have the part.

 

[SKYCHENEY]

https://www.acadianmarinetransmission.com/

 

[Captain Ralph]

https://www.acadianmarinetransmission.com/

AND Yes, SKY had provided an address to a good site that can help.

 

[Hatteras58]

Thanks guys for the quick response. On my last cruise (3 hrs) it appears that about 1.5 gal of engine oil got into the transmission. Based upon what I’ve read about this problem on the HOF and elsewhere, I’m guessing the rear seal on the engine is the issue. The M20 has been operating fine and I don’t have any reason to believe there are other problems with the tranny. I’m going to help a mechanic pull the unit back so we can replace the seal. I just wanted to identify the gaskets and seals we will need the put things back together before we actually start the job. Sounds like I should call Acadian for some advice on what parts to get, right?

 

[rsmith]

Gallon and a half? That doesn’t even sound possible. Typically if the rear main is leaking it just tints the trans oil. Mine did for years until the last rebuild. It’s not a pressure situation just the oil level in the engine. If you really did have that much oil in the trans something else is going on. I’d look at the crankcase pressure before I ripped the trans apart.

 

[Hatteras58]

I spoke with Acadian Marine and they too believe it's a problem with the rear seal on the engine. I ordered an oversize seal with sleeve and the other gaskets necessary to reinstall the Allison. Before leaving for the 3.5 hr cruise home, I emptied 1.5 gallons of oil from the transmission which brought it back down to the 'full' level. We kept a close eye on the engine oil pressure underway and after 1-1/2 hours of running, added 5 qts of oil to the engine. Then again at 2.5 hours into the trip, added another gallon. Haven't check yet but I suspect that engine is low another gallon or so at the end of the trip.

I am not looking forward to pulling the transmission back for this repair!

FYI, Acadian is charging $425 for a rebuild of the Hydreco pump for the M20.