Hatman
I agree with you 100%. Drain the old fluid, install a new filter and refill with new oil and then unhook the cooler out to transmission line and start the engine and manually shift to reverse-1st-netrual-reverse 1st-netrual-stop the engine-add more oil-start the engine and repeat until oil runs out clear like new.
***REMEMBER***
One tiny speck of dirt could kill your transmission. Use a pressure air hose to clean the disconnect fitting before and after loosening. Then proceed to open the line and run the old oil out the cooler line.
Plan on needing about the same amount of oil as is required to overhaul the transmission plus a couple quarts more for the cooler.
When you know your Allison has "TRANSYND OIL" forget about the drain period for several years and then oil sample analysis will tell you when to change it.
Allison will not endorse this procedure because of the dirt risk but how much dirt entered the transmission all the years they required us to remove the oil pan and the valve body etc.to change the filter?
