Allison Gear Manual

I am looking for the service manual for the Allison Marine Gear in my 1981 Motoryacht, gear number M15. I am experiencing some slugishness in the port gear when engaging either forward or reverse. I understand there is a valve assembly on the top of the gear at the shift point, and further that it can be rebuilt. Would this rebuild solve this problem or might it be somewhere else internal to the gear? The manual would be a great help. Please contact me at 313-220-6081 or email at dakrhon@comcast.net. I am willing to pay for manual.

I have had my selector valve apart and there is little that can go wrong with it. I doubt that the valve is the problem. It is more likely a clutch pack

PROBABLY the clutch pack or the piston assembly that engages it.

The gear has to come out to fix either.

If you pull one for rebuild make sure you get a BINDING estimate before you have the work done - parts and labor. In many cases you can BUY a new Twin Disc either for the price of the rebuild or very close to it.....

I know it is basic, but is the pressure ok and is the level full when idling. Also check the screen and change the filter. I had a boat recently where there was remnants of a rag in the screen. Sluggishness in both fwd and rev sounds like a pressure problem.

What are the gear pressure readings before and after you try to shift into gear?

Does it go into reverse better than it goes into forward?

The answers to these questions may lead to a very simple fix you can do yourself, if you have an air leak at the suction side of your hydro pump, like I did, or even a bad pump, which yoou can fix yourself with a new seal kit.

Fixing the gear costs thousands. Fixing the pump costs less than $100. I hope it's the pump.

BTW - Maybe you should move this thread to the General Discussion section. You can get more readership and active answers there.

Doug Shuman

I moved the thread to "General".

A good point was made - post your gear pressure readings when out of gear at idle and at 1500 RPM (neutral), then at idle when shifting and once the shift is complete.

That'll help.

Also, do check for suction airleaks, clogged gear oil filters, a clogged strainer, and I assume you've checked for proper oil level, yes? Note that the oil level must be checked with the ENGINE RUNNING, IN NEUTRAL.

If the gear is not HOT then you want to be filled to just above the "LOW" line. DO NOT OVERFILL these gears! By the same token, at or below "LOW" hot is too low! Ideal is right in the middle with the gear at operating temperature.