It is a Mack manual transmission. It features in Mack tradition a 5 speed main box and a 2 speed transfer case integrated into a single package. The transfer case is a separate casting bolted to the back of the main box, but the output shaft is a single long shaft reaching through both boxes. The main box is of the constant mesh type in that the gears are always engaged and a small shifting spline slides to lock the proper gear to the output shaft. It is not a synchro-mesh transmission, in that the extra hardware to synchronize the gears is not present. The oil compartment of the main transmission and the transfer case are separate. Each has its own level plug and they are at significantly different elevations. The second lubrication circuit and the one that causes the grief is in the input shaft. There is a splash catcher high on the right side of the main box. This catch basin has a cast drain hole that runs forward and down and around to the front main bearing.The input shaft is rifle bored and oil is inserted into the center of the input shaft in this area and pushed backwards to oil the needle bearings between the input shaft and the output shaft and is further pushed into the front of the output shaft to oil the second, third and fourth gears which ride on the output shaft. A small bore riding piston pushes the oil into the input shaft circuit. The sealing to the front is accomplished with 2 sets of spiral threads machined into the input shaft. The primary 'screw' is about half an inch long, and is supposed to screw the oil to the rear as the input shaft turns. It screws within a presumably close fitting surface on the inside of the collar that bolts over the front of the transmission.
