M 135, M 211 Transmission Oil

[M543A2]

I used one of these trucks for years for farm grain hauling, pulling a 30 foot trailer, and plowing snow with no transmission problems. When I first got the truck a friend of mine who worked on these in the military that had a transmission shop told me to get the engine oil out of the transmission ASAP and replace it with ATF. He built these for racing at the time, saying they were a good transmission. His thought was that the military used engine oil was that the supply line was not well adapted at the time to including special oils like the ATF. My experience did not correlate with so much bad press about this transmission in the military trucks so something had to be happening and I think it was because of owners staying with the engine oil in them.
At a local sale I bought quite a few old military truck manuals going back to the 1940 to 1941 era. I also got owner's manuals for some civilian trucks in the early to mid 1950 era. One was for heavy duty trucks using this transmission. I have attached GM's specifications out of that manual for the Hydramatic oil. It was too big to copy normally so it is sideways, hope you can read sideways! They do not want engine oil in the Hydramatic at all, but in an emergency it can be added but must be changed out for pure ATF ASAP. I hope this along with my experience halps to clarify why I have been telling owners of these trucks to change out the engine oil if that is what is in their transmissions ASAP for long life. Change it to ATF, run it for about a hundred miles or so, drain and refill with ATF again to get all of the engine oil out of it.
Don't forget to take the cover off the front of the transmission oil pan and clean out the crud that might be hindering cooler operation.

 

[USMC 00-08]

Great info!! Thanks!! Every time I have pulled the cover off of the cooler in various trucks, there has been a lot of crud settled in the bottom of them.

For discussion sake, what do you think of the write up that recommends Hytran in the transmission? It's sure hard to argue with the success you had with your truck.

https://www.steelsoldiers.com/showthread.php?17023-Hydramatic-Heaven

 

[M543A2]

Very good dissertation, thanks for the reference to it! I always shifted my truck like he describes.
Obviously oils like Hytran were not available when the manual I have was written. I believe it would be an excellent choice but have not used it in the truck, so I cannot speak from experience. I believe I remember Allison saying you can use that type of oil in their transmissions. The fellow in the article had very good luck with it, using his trucks like I did, and I agree with his statements about compatibility with the older frictions.

 

[yodraino]

Hi for what it's worth I rebuilt my transmission and after talking to a lot of different people I decided to run hy Tran I have roughly a thousand miles on this transmission everything seems to work flawless I can't tell you too much on how it shifts because I put a manual valve body in this transmission.