The Allison 2500 HD transmission is a heavy duty transmission typically equipped on work trucks and motor homes. These massive transmissions require much more fluid than a typical transmission,with the Allison 2500 HD using up two 15 quarts of transmission fluid, about four times more than a typical vehicle. The fluid in these transmissions should be changed once ever 50,000 miles, or every 25,000 miles if your vehicle is subjected to heavy loads.
Locate the drain plug of the transmission case. It will be underneath the vehicle, towards the center.
Place an oil pan underneath the drain plug, and unscrew the plug using an adjustable wrench. Allow the fluid five minutes to drain out.
Screw the drain plug back into the transmission oil pan.
Remove the bolts around the drain pan using a socket wrench with a socket wrench extension.
Pull out the drain pan slowly, being careful not spill fluid. This will expose the transmission fluid filter.
Remove the two bolts that hold the transmission fluid filter in place with a socket wrench and extension.
Place the new filter in its place and bolt it in using a socket wrench and extension.
Bolt the drain pan back into place.
Open the hood and remove the transmission fluid dipstick from the transmission fluid dipstick tube.
Place a funnel in the tube and refill the transmission with DEXTRON III automatic transmission fluid. Check the fluid level occasionally with the dipstick until the fluid reaches the fill line.
