Life of Allison M-15 Transmission Seals

[bobk]

I'm posting this regarding life expectancy of an M-15 transmission. Maybe it will help someone in the future.

The boat is a 1981, 6V92TA's from 1980. Two years ago, 29 years old, I lost foward on the starboard transmission due to bad seals. Clutches and pump were fine. Engine hours about 4000 and presumably this was the first major service on the transmission.

Last week I had the port transmission removed for R&R of the rear main seal. About 4500 hours on it and 31 years old. The transmission was still seemingly OK but we were doing the rear main seal so WTH. The mech found the foward clutch seal was hard and had a crack. This was another disaster waiting to happen on the waterway away from home. Caught it in the nick of time. Again the clutches were fine, but this one had a very slow leak in the pump seal. I have no record of prior service on either of these.

I don't know if the end of service life is related to age or hours, but 30 years/4000 hours ought to be the time to start to worry.

Cheers,
Bobk
1981 48MY
Chateau de Mer

 

[Canuck Dennis]

I thought the M series were rate3d for under 350 HP ?

 

[bostonhatteras]

Got you beat on those hours and age. Two m 20 gears going strong after 40 years and over 5000 hours. The boat is '70 45' convertible that was originally set up as a hardcore fisherman with giant tower and 6' pulpit. It went to fla from ma every year for 10 years plus and it's original name was jealous lady owned by joe falconi of Boston area. The engines have new cyl heads and injectors but all the gears have ever had are oil changes and converted to spin on filters with new lines. I would say they should be durable, they are rated for full throttle shifting, I believe.

 

[bobk]

Got you beat on those hours and age. Two m 20 gears going strong after 40 years and over 5000 hours. The boat is '70 45' convertible that was originally set up as a hardcore fisherman with giant tower and 6' pulpit. It went to fla from ma every year for 10 years plus and it's original name was jealous lady owned by joe falconi of Boston area. The engines have new cyl heads and injectors but all the gears have ever had are oil changes and converted to spin on filters with new lines. I would say they should be durable, they are rated for full throttle shifting, I believe.

Interesting. I hope to hear other similar experiences. Then I'll have to wonder if the formulation for the seals changed of the oil was different or if mine overheated sometime in the past. Thanks for the info.

Bobk

 

[bostonhatteras]

I believe there was a recall performed on these gears back in the 1970s. It seems there was an issue with oiling of some of the bearings. I can't recall the specifics right now, but I will look into it and post that.

 

[SKYCHENEY]

I thought the M series were rate3d for under 350 HP ?

Guess not. I have M gears mated to 465hp 6v92TA's.

 

[mike]

I believe there was a recall performed on these gears back in the 1970s. It seems there was an issue with oiling of some of the bearings. I can't recall the specifics right now, but I will look into it and post that.

You are correct the issue was the early units did not have pressurized oil delivery to the main shaft bearings. On early units upper bearing oiling was provided by splash from the gears. The fix required "gun" drilling a 0.090 bore to the main shaft oil passage. This path provides pressured oil to the outer bearing. The inner bearing fix required drilling a 0.090 passage into the center oil gallery that delivers oil from the selector valve to the main shaft. Made the mods on my two 1972 (4k hrs) units, and have the DD/Allison doc if anyone is interested.