M35A3 Allison Transmission Fluid Change Out

[glcaines]

My M35A3, as received from the U.S. Army, had 10W-30W motor oil in the Allison 1545 automatic transmission. The Army used motor oil to eliminate one more fluid they needed to support. I have now changed out the motor oil with fresh Dexron III ATF. I used the repetitive drain and fill technique to purge the system of motor oil. What a difference! The transmission shifts much smoother now and runs cooler. The lock-up feature is also much smoother. I'm absolutely amazed at the difference. I also changed out the external filter and plan to change out the internal filter, but have not done so yet. Originally, I planned to upgrade to Castrol TranSynd synthetic ATF that was designed for the Allison transmission. I purchased a 5 gallon (US) pail of the TranSynd fluid, but now I think I will sell it and stick with the Dexron III.