Allison 3000 transmission leak

[a4epilot]

Have a very small transmission leak. Lose about 1 qt every 2000 miles or so. Because it's so small and the airflow spreads the fluid all over, it's impossible to determine where it's coming from. Gets on my towed.

Been to 2 Allison service centers and they cannot tell either. They both cleaned the transmission case and I drove it around for a while and then returned for an inspection. The leak was so small that no fluid was visible. They both confirmed it is not a leaking driveshaft seal.

I have always used the transmission control panel electronic fluid level feature to determine fluid level.

When it began, there had been no recent servicing of the transmission. I did replace the filters and related seals just in case that might have been the issue but it was not.

It has not been overfilled and therefore not a possible issue with too much fluid and venting outside at the top of the case.

Looking at the pics, it might appear obvious the leak is the pan seal or the verticle case seal but I don't think so. It appears to collect there only after being driven for many miles. When it is cleaned and then driven, there is no apparent leak anywhere including there. However, that's not to say it isn't a possibility. The only way to know for sure would be to replace both one at a time. If I do anything, I'd replace the pan seal first. Any thoughts about that??

Replacing a qt every few thousand miles in itself is not a problem. The main issue is the fluid sticking to the underside of the case and chassis and worst of all, all over the right side of my towed collecting dirt and diesel exhaust, a mess, and damaging the paint.

Haven't read anyone posting anything like this but hoping someone might have an idea or two.

Thanks in advance.

Gary K

Edited October 17 by a4epilot
Additional info added

[jacwjames]

Do you see any oil coming out of the bottom hole on the bell housing??

Dropping the pan isn't that bad, after we bought our coach I didn't have any maintenance history at all.  So the first time I changed fluid I dropped the pan just to see if there were any issues.  Didn't see any, put everything back together

So I you think it might be the pan I'd drop it and check to see if you can see a problem with the gasket, which if in doubt I'd replace.   

[Ray Davis]

I suppose you or someone has made sure the bolts are snug,  Outside of that you may have to start replacing gaskets.  As Jim said they are not too bad a job.

Might be a good time to service the transmission too.  The reddish color that I see, is that leaked fluid?

[a4epilot]

All bolts were retorqued. 

Serviced when replacing filters and seals. No issues.

Gary K

[cbr046]

I just "washed" my radiators for the second time.  The oil gets in the fins that attracts dirt and starts limiting air flow.  Probably not enough oil in your case but watch your engine temp anyway.  I used SuperClean, BTW. 

- bob

[Ray Davis]

Jim asked about the bottom hole in the bell housing, we can't see it in the pictures but is it oily in that area?    There is a seal up there, so it could leak.   I'm not sure why but they don't plug that hole.  However, I might be tempted to wad a rag & screw it in there for a while.  If the oil is coming from there it should stop & turn the rag red.

[a4epilot]

Side radiator so no problem. 🙂

[Ray Davis]

1 minute ago, cbr046 said:

I just "washed" my radiators for the second time.  The oil gets in the fins that attracts dirt and starts limiting air flow.  Probably not enough oil in your case but watch your engine temp anyway.  I used SuperClean, BTW. 

- bob

Gary has a side radiator that pulls the air from outside & moves it across the engine.  Pretty much eliminates the oil + dirt radiator problem.

You are right though, rear radiators are inclined to collect stuff.

[a4epilot]

3 minutes ago, Ray Davis said:

Jim asked about the bottom hole in the bell housing, we can't see it in the pictures but is it oily in that area?    There is a seal up there, so it could leak.   I'm not sure why but they don't plug that hole.  However, I might be tempted to wad a rag & screw it in there for a while.  If the oil is coming from there it should stop & turn the rag red.

Not familiar with the "hole." Have to check it out. However, if that were the problem, the 2 Allison dealers should have found it, I'd think. One dealer had 2 guys looking for over an hour.

[Ivan K]

I use a dye and UV light, in fact I just put it in the toad to find a leak. It should make it pretty obvious.

[a4epilot]

1 minute ago, Ivan K said:

I use a dye and UV light, in fact I just put it in the toad to find a leak. It should make it pretty obvious.

Probably, will take to another Allison service center soon and ask about doing that.

[bobdinsmore]

I'm guessing, but based on experience with cars, if there is a transmission cooler check its connection arrangement to the transmission. I just had a steel tubing rust out between the transmission and the cooler.

[a4epilot]

The leak is coming from transmission. 

[CTerry]

Not an expert here but those overlapping gaskets do not look right to me.

[96 EVO]

1 hour ago, CTerry said:

Not an expert here but those overlapping gaskets do not look right to me.

Doesn't look right to me either, but, you would think a qualified Allison shop would spot that!

[jacwjames]

5 hours ago, CTerry said:

Not an expert here but those overlapping gaskets do not look right to me.

I took another look, something doesn't look right with the gasket(s). 

Dropping the pan would confirm pretty quickly if that was the problem. 

[Ivan K]

I suppose you won't be dropping the 'pan' yourself? It is a lot more than just a hollow pan and pretty heavy.

[Ray Davis]

3 hours ago, 96 EVO said:

Doesn't look right to me either, but, you would think a qualified Allison shop would spot that!

They would have to actually crawl under and look at it.  👀

I agree, it looks like 2 gaskets.

[a4epilot]

5 hours ago, 96 EVO said:

Doesn't look right to me either, but, you would think a qualified Allison shop would spot that!

It came that way in 2006. Never leaked until 2 years ago so I wouldn't think that's the problem.

I will be taking it to a 3rd Allison Service Center soon. The only reason I posted this problem was in hopes that someone had the same problem and had the answer.

Thanks.

Gary K

[96 EVO]

Your probably right, it's just strange to see two gaskets overlapping!

I would show your pictures to the next Allison shop before they inspect.

It's too bad your thread was a couple of weeks after I changed my fluid and filters, cause I could have inspected that area on mine while I was under there.

Edited October 19 by 96 EVO

[dl_racing427]

On 10/17/2023 at 1:30 PM, Ray Davis said:

Jim asked about the bottom hole in the bell housing, we can't see it in the pictures but is it oily in that area?    There is a seal up there, so it could leak.   I'm not sure why but they don't plug that hole.  However, I might be tempted to wad a rag & screw it in there for a while.  If the oil is coming from there it should stop & turn the rag red.

That hole is open to prevent moisture or leakage from filling up the converter housing.

On 10/18/2023 at 8:07 PM, 96 EVO said:

Your probably right, it's just strange to see two gaskets overlapping!

I would show your pictures to the next Allison shop before they inspect.

It's too bad your thread was a couple of weeks after I changed my fluid and filters, cause I could have inspected that area on mine while I was under there.

It looks like there is a plate between the two gaskets.
Look at the left of the pic just below the bottom horizontal bolt.

[Rico K 2005 Knight]

On 10/17/2023 at 12:13 PM, a4epilot said:

Have a very small transmission leak. Lose about 1 qt every 2000 miles or so. Because it's so small and the airflow spreads the fluid all over, it's impossible to determine where it's coming from. Gets on my towed.

Been to 2 Allison service centers and they cannot tell either. They both cleaned the transmission case and I drove it around for a while and then returned for an inspection. The leak was so small that no fluid was visible. They both confirmed it is not a leaking driveshaft seal.

I have always used the transmission control panel electronic fluid level feature to determine fluid level.

When it began, there had been no recent servicing of the transmission. I did replace the filters and related seals just in case that might have been the issue but it was not.

It has not been overfilled and therefore not a possible issue with too much fluid and venting outside at the top of the case.

Looking at the pics, it might appear obvious the leak is the pan seal or the verticle case seal but I don't think so. It appears to collect there only after being driven for many miles. When it is cleaned and then driven, there is no apparent leak anywhere including there. However, that's not to say it isn't a possibility. The only way to know for sure would be to replace both one at a time. If I do anything, I'd replace the pan seal first. Any thoughts about that??

Replacing a qt every few thousand miles in itself is not a problem. The main issue is the fluid sticking to the underside of the case and chassis and worst of all, all over the right side of my towed collecting dirt and diesel exhaust, a mess, and damaging the paint.

Haven't read anyone posting anything like this but hoping someone might have an idea or two.

Thanks in advance.

Gary K

Just a thought. They have pretty inexpensive Bluetooth cameras out there these days. May be an idea to strap a camera underneath focusing on the transmission and someone can watch it on their phone while you drive. Sounds weird but might be cheaper and quicker than changing parts until you find it.

[a4epilot]

Been thinking that exact same idea. Thanks.

Gary K