I have a 2004 Mack Granite I got recently with the 427 and Mack transmission. For the life of me, I cannot downshift it. It upshifts totally fine, but it will not downshift. Other people have tried and cannot get it to downshift. It only grinds. Sometime it can be forced to downshift, but will grind the whole time.
Tried it all different ways, speeds, etc. It just will not downshift.
What could be wrong with the transmission m ? I think something is wrong with it. Considering swapping for an 8LL...
