trans fluid - M923A2

[FXR1969]

Searched and searched best thing I can tell is use dextron 3 in it
whats every one else opnion??
1991 m923 a2

 

[Ford Mechanic]

15w40 oil per the TM. Other folks have tried other stuff

 

[swede69]

I use oil. you will spent a lot of money to properly flush and fill. allison says oil is used under hd application.

 

[Ultra Mag]

I use Trans Guard synthetic,150.00 for 5 gal made by Valvaline I think

 

[emr]

Do what the military did and does, Its time tested and works, 10 wht is standard for most climates. swede69 is on it... that's the facts ...

 

[Csm Davis]

10wt is what it came with from the factory and the military changed to using 15w40 for easier logistics, bet you good money none were drained and refilled just to change from one to the other.

 

[idbankrman]

I bought three trucks from Ft Hood that were completely drained. Normally I run 15W40 in the tranny but I decided to experiment with a NAPA heavy duty tractor and hydraulic transmission oil in the M934A2. Its basically a 15 weight oil. Well I cant tell any difference at all. I would stick with the 15W40 since that makes just one type of oil you need for both engine and transmission. It also accomadates the widest climactic conditions.

 

[idbankrman]

If you get a truck that has dexron III in it you can continue using it or just drain the tranny and refill with 15W40. No need to flush as the Dexron will mix with anything and the transmission will not care.

 

[jjb]

Do what the military did and does, Its time tested and works, 10 wht is standard for most climates. swede69 is on it... that's the facts ...

HaHaHa

Were you trying to make a joke with that statement?

Doing what the military does will only cost you big money the down the road when it comes to fluids. They replace the engines/trans in these trucks with only 20k or so miles on them.
They used 15w40 in Detroit in my HEMTT. Anyone who knows anything about 2 stroke diesels will tell you that destroys them.In commercial use they routinely saw 500k miles with the proper oil and regular maintenance. They barely make 30k in the military.

Just call Allison and ask them what oil you should run in your trans. They will tell you 10wt or 15w40 will work but they will severly shorten the life of the transmission.

I prefer to listen to the people who actually manufacture the engine/trans they know better than uncle sam what should go in them.

 

[juanprado]

mine came with dexron already in the tranny and power stg. I have changed the spin on several times and dropped the pan filter last year. I refill / top off with dexron. Cheap and has always shifted smooth.

my .02

 

[idbankrman]

Allison's own manual includes 15W40 right along with 10W and Dexron III. If oils other than Dexron III were the cause of vastly shortened life I dont think Allison would be recommending them. For operations in temps below 5F Dexron III is a better choice than 15W40 due to the 20 minute warm up time before shifting from neutral. Still if only occasionally wanting to drive your truck below 5F I would probably still stick with the 15W40. Allison also recommends changing the oil every year. Wonder how many people actually do that?

 

[jjb]

Allison's own manual includes 15W40 right along with 10W and Dexron III. If oils other than Dexron III were the cause of vastly shortened life I dont think Allison would be recommending them. For operations in temps below 5F Dexron III is a better choice than 15W40 due to the 20 minute warm up time before shifting from neutral. Still if only occasionally wanting to drive your truck below 5F I would probably still stick with the 15W40. Allison also recommends changing the oil every year. Wonder how many people actually do that?

Take a look at their current recommendations. Only TES295 and TES389 approved fluids are recommended and they do not include 15w40. That is designed as an engine oil not transmission oil.

I have called Allison and asked. They explained why the military uses 15w40 and its not because its the best fluid.

Do what you want but spending an extra $100 or $200 for the manufacturers recommended fluid is much cheaper than spending thousands on a new transmission.

 

[Csm Davis]

jjb your own list shows military spec fluids are accepted in military trucks, also these trucks didn't start life with 15w40 which was chosen to make logistics easier they started life with 10wt which at the time was chosen because of the hard use they were expecting the trucks to endure. If you will back up and read the other post about the subject on here you will see that these trucks and the transmissions in them did hold up extremely well. But I have seen several post of failure shortly after switching to automatic transmission fluid so I think I will stay with what the military has run millions of miles and Allison warranted originally to be the correct fluid for the job, 10wt.

 

[wheelspinner]

Take a look at their current recommendations. Only TES295 and TES389 approved fluids are recommended and they do not include 15w40. That is designed as an engine oil not transmission oil.

I have called Allison and asked. They explained why the military uses 15w40 and its not because its the best fluid.

Do what you want but spending an extra $100 or $200 for the manufacturers recommended fluid is much cheaper than spending thousands on a new transmission.


View attachment 611821

What manual is that from? Its talking about MY 2009 and 2010, as well as "Commercial On Highway Products"Seems like this is a possibly recommendations from a vastly different product than the brain dead HD MT transmissions we are talking about. Maybe I'm wrong but it sure seems like it.

 

[Coffey1]

Here's my take on this subject when I had to change transmission on a truck I talked with a Allison service guy not one that stands behind a counter but one who takes these apart. He had to take my converter apart
And clean and check it because the converter that came with transmission was for 250 not the 8.3

He said the 10wt or 15-40 would be find to use also dex would work.
The only reason not to use dex is if you use your truck pulling trailer with load or truck loaded or off roading due to dex has lower boiling point and transmission will over heat.
Heat is the killer of these transmissions.

As far as fluid change

1 drain tranny
2 change filters
3 put new fluid in
4 remove return line from tyranny from oil cooler
5 put line in bucket start truck keep adding fluid until what come through return line looks like what your putting in this will also flush converter

 

[jjb]

What manual is that from? Its talking about MY 2009 and 2010, as well as "Commercial On Highway Products"Seems like this is a possibly recommendations from a vastly different product than the brain dead HD MT transmissions we are talking about. Maybe I'm wrong but it sure seems like it.

It includes the HT and MT series.

 

[Csm Davis]

It includes the HT and MT series.

And it doesn't back up your statement. The only mention of the MT is that it can use the military spec fluids.

 

[jjb]

And it doesn't back up your statement. The only mention of the MT is that it can use the military spec fluids.

I'll upload the whole document later but like I said I spoke to Allison directly and they said it will work but it will shorten the life of the trans. Do what you want it's your money.

 

[Csm Davis]

I'll upload the whole document later but like I said I spoke to Allison directly and they said it will work but it will shorten the life of the trans. Do what you want it's your money.

Okay jjb I understand what you are getting at and I am not trying to mean or argumentative but hopefully save you and or someone else the money of a transmission rebuild. If you are going to be running up and down nothing but asphalt and not putting a heavy load on your truck go for it run a different fluid that will make it shift softer like a car, but if you are going to treat these trucks like the military designed them to be used and Allison specified the transmission to use 10wt because of the use then I would use the original fluid. Also did the Allison person you talked to have anything to do with specifications of the the original setup back in 1984? Or even a fluid specialist for Allison or just some guy who you happened to get on the phone? I have lots of Allison and military data behind my recommendation of 10wt and many many trucks on the road and off that have run for years.

 

[jjb]

Okay jjb I understand what you are getting at and I am not trying to mean or argumentative but hopefully save you and or someone else the money of a transmission rebuild. If you are going to be running up and down nothing but asphalt and not putting a heavy load on your truck go for it run a different fluid that will make it shift softer like a car, but if you are going to treat these trucks like the military designed them to be used and Allison specified the transmission to use 10wt because of the use then I would use the original fluid. Also did the Allison person you talked to have anything to do with specifications of the the original setup back in 1984? Or even a fluid specialist for Allison or just some guy who you happened to get on the phone? I have lots of Allison and military data behind my recommendation of 10wt and many many trucks on the road and off that have run for years.

That may have been true years ago but fluids have come a long way. I have spent lots of time researching what the right fluids are and the resources I have talked to I would consider experts. Like engineers who have intimate knowledge of how these transmissions work.

I didn't want this to turn into debate about trans fluid. I wanted to point out that just doing something because the military does it is just plain dumb. And telling other people to do the same especially people who are new to these vehicles is not fair to them. Like the example I used of the Military using 15w40 in a Detroit 2 cycle engine which will ruin it quick.