The Allison transmission is a heavy duty automatic transmission designed for larger trucks. Changing the fluid is not the same as changing the fluid in a regular car or truck. The system is more prone to metal chard and debris getting into the transmission. Flushing the fluid rids the system of all the old transmission fluid and any debris that is caught up in the transmission. Your Allison Transmission will be able to get any job done for many miles by regularly flushing and changing the fluid on a regular basis. Do not forget to replace the filter at every fluid change as well.
Park the truck on a flat level space and make sure the parking brake is set.
Place a large drain pan underneath the transmission. Locate the drain plug at the bottom of the transmission drain pan.
Unscrew the drain plug with a socket wrench. Allow all the fluid to drain out.
Locate the cooler return line which is labeled "From Cooler". The lines are located next to the transmission filter. Pull the retaining clip, out of the way with a small flat head screwdriver. Pull the line out and place a 5/8-inch plastic hose over the line. Insert the other end of the line into a gallon jug.
Unscrew the transmission filter with an oil filter wrench. Pull the filter down and take the magnet off the top of the filter. Clean any debris off the magnet and place it on the new filter. Fill the filter with automatic transmission fluid and lubricate the gasket. Rub transmission fluid around the gasket with your fingers. Tighten the filter back to the filter housing by hand. Do not wrench tighten as this will strip the threads of the filter.
Open the hood to access the transmission fluid fill pipe. Take the dipstick out and insert a funnel into the fill tube. Pour 8 quarts. of the recommended transmission fluid in to the funnel.
Make sure the hose is sunk into the fill bottle. You may need a partner to help by instructing them to start the truck so you can watch the bottle. You will need to be sure that no more than 2 quarts of fluid gets pumped out into the tube. Turn off the truck when 2 liters have flowed into the gallon container. Dump the 2 liters into the waste transmission fluid. Replace with an additional 2 liters of transmission fluid into the fill tube.
Place the hose in to the gallon container. Be sure to set the brake and then start the truck. Engage each gear while holding it for one second. Bring the shifter back to the park or neutral position and turn the truck off. Make sure you do not lose more than 3 liters of transmission fluid to the container.
Dump the old transmission fluid out and replace with 3 liters of new transmission fluid. Repeat the process one more time to be sure the transmission fluid coming out of the return line is clean. Replace any fluid lost.
Push the cooler return line back to the transmission. Make sure you place the locking ring back toward the top of the line to lock it in place.
Check to be sure the fluid level reads full. If not add more fluid a liter at a time. Drive the truck for at least an hour and check the fluid one more time to be sure the level is accurate.
