How to perform Allison Transmission filter and fluid change?

It has a drain plug. Remove the drain plug, it will drain. It has a spin on filter (Allison Part #29539579), remove and replace with new. Put the drain plug back in and refill with appropriate fluid. If the transmission is in a GMC or Chevrolet 2500 or 3500 series truck the appropriate fluid is Dexron VI. Anything else and the appropriate fluid is Transynd. There are two pan depths availabe: shallow and deep. Refill after service takes 7.4 for shallow and 10.6 for deep. There is a internal filter, but it si only changed during a transmission overhall. If you needed to read this to know how to change the fluid, you should carry it to a dealer.