Allison Transmission had low oil, would not engage in forward

[osonegro]

After a 200 mile run from Manzanillo, Mexico to Ixtapa, my port engine would not go into foward when we were leaving the anchorage. I checked the oil in the transmission and it showed to be below the low mark. I put almost 4 qts of fresh 40W oil in and the transmission engaged. Now when I check the oil with the engine running it looks kind of brownish and not the normal oil color. I want to know if I'm in trouble and what to do from here. I am thinking of draining all the oil from the transmission and filling with new fresh oil.

[saltshaker]

After a 200 mile run from Manzanillo, Mexico to Ixtapa, my port engine would not go into foward when we were leaving the anchorage. I checked the oil in the transmission and it showed to be below the low mark. I put almost 4 qts of fresh 40W oil in and the transmission engaged. Now when I check the oil with the engine running it looks kind of brownish and not the normal oil color. I want to know if I'm in trouble and what to do from here. I am thinking of draining all the oil from the transmission and filling with new fresh oil.

Any signs of oil leaks? What's the engine oil level look like? Does the oil look dark or milky brown? Does the oil look normal after the engines are shut down and set for an hour or so? If you overfilled them the oil will get aerated and look milky but clear up after it sits. Not a big deal but you do need to get it to the proper level if this is the case. In order to get an accurate reading the oil needs to be checked when the unit is running and preferably up to temp.

[Jasper]

Unfortunately I have had a lot of experience with this problem and Allison Gear Boxes. A quick education I have paid dearly for. I still have a lot to learn before I am at the level of some of the Senior Members here, but maybe I can point out some things to look for. As Saltshaker has asked, is there an oil leak? If not:
What is the oil pressure of the gears in idle?
What is the oil pressure of the gears in Forward?
Is there a "burnt oil" smell?
When you checked the oil level, was the engine running?
Have you checked the screen/filter? You will find this on the hose going into the oil pressure pump.
Is the oil pump a Hydreco?

The fact that the gear now engages with an oil fill up is a good sign that you may have saved the clutch and other parts. It may be a pump problem which is a relatively cheap fix. The lack of oil and oil pressure can burn your clutch away. Find out why before using the boat, it may save you a lot of trouble.

[AL BAUMER]

Try filling with oil, then check filter, right side of gear under 3 bolts. If full of metal, you will have to rebuild gear. If not Hydreco pump may be bad. This is located on ( I think ) left accessory drive rear of engine.

[AL BAUMER]

Strange as it may seem, these gears will engage in reverse with low oil pressure, but not in forward. Had 1973 58YF, 8V71TI with Allison M gears, and 1979 58CY 8V92TI.

[osonegro]

Any signs of oil leaks? What's the engine oil level look like? Does the oil look dark or milky brown? Does the oil look normal after the engines are shut down and set for an hour or so? If you overfilled them the oil will get aerated and look milky but clear up after it sits. Not a big deal but you do need to get it to the proper level if this is the case. In order to get an accurate reading the oil needs to be checked when the unit is running and preferably up to temp.

No sign of oil leaks. Engine oil level is OK. The oil in transmission looks milky light brown. I've not checked what the oil looks like after shut down. Will do that tomorrow. I checked the oil with the engine running and filled until it was at full mark on dip stick. The engine does engage in forward and reverse.

[Tim Powell]

Unfortunately I have had a lot of experience with this problem and Allison Gear Boxes. A quick education I have paid dearly for. I still have a lot to learn before I am at the level of some of the Senior Members here, but maybe I can point out some things to look for. As Saltshaker has asked, is there an oil leak? If not:
What is the oil pressure of the gears in idle?
What is the oil pressure of the gears in Forward?
Is there a "burnt oil" smell?
When you checked the oil level, was the engine running?
Have you checked the screen/filter? You will find this on the hose going into the oil pressure pump.
Is the oil pump a Hydreco?

The fact that the gear now engages with an oil fill up is a good sign that you may have saved the clutch and other parts. It may be a pump problem which is a relatively cheap fix. The lack of oil and oil pressure can burn your clutch away. Find out why before using the boat, it may save you a lot of trouble.

Jasper and Jack
with no sign of oil leak where would a gallon of oil go? I do understand what Jack said about settling down and air being in it but a gallon.

[osonegro]

Unfortunately I have had a lot of experience with this problem and Allison Gear Boxes. A quick education I have paid dearly for. I still have a lot to learn before I am at the level of some of the Senior Members here, but maybe I can point out some things to look for. As Saltshaker has asked, is there an oil leak? If not:
What is the oil pressure of the gears in idle?
What is the oil pressure of the gears in Forward?
Is there a "burnt oil" smell?
When you checked the oil level, was the engine running?
Have you checked the screen/filter? You will find this on the hose going into the oil pressure pump.
Is the oil pump a Hydreco?

The fact that the gear now engages with an oil fill up is a good sign that you may have saved the clutch and other parts. It may be a pump problem which is a relatively cheap fix. The lack of oil and oil pressure can burn your clutch away. Find out why before using the boat, it may save you a lot of trouble.

The oil pressure with the gears in idle and Forward is normal now. I havn't checked for a burned oil smell but will do that tomorrow. The oil level was checked with engine running. Everything is stock on the trans so I don't know if the oil pump is Hrdreco.

[MikeP]

Rebuilding the pump, should that prove to be needed, is quite easy and the parts kit is around 80 bucks. The seals get old/brittle and may not seal well after many years of use. If the tranny pressures are in spec, or can be adjusted to be in spec, then the pump is ok. I seem to recall that the pressure is supposed to be 130PSI at 1800 RPM in forward but don't hold me to that…look it up.

[osonegro]

As I said in the first post, the trans not engaging occurred after a 200 mile run from Manazanillo to Ixtapa, Mexico. On arrival in anchorage the trans engaged fine while setting the anchor then we sat there for 2 days at anchor. The problem did not show itself until we were trying to get underway and that's when I discovered the low oil condition in the port engine transmission. I know to check the oil with the engine running, but the first thing I noticed was a low oil pressure on that transmission. Now the oil pressure is OK and the oil is up to the full mark but the color is cloudy and a light brown.