Abstract: A family of transmission assemblies is provided that includes both manual and automatic shifting versions. The family utilizes a casing assembly having an interchangeable central housing portion that will receive either a manual or an automatic transmission mechanism. Both the automatic and the manual transmissions utilize an input shaft member, an output shaft member, a countershaft member and a reverse/idler shaft member that are oriented along parallel operating axes and that are disposed in a geometric array which is common to both the automatic and the manual versions. The casing assembly has a central housing portion that has at least a front and rear opening, and a series of supporting axes--one for each of the operating axes defined by the shaft members that are common to both the automatic and the manual versions. The supporting axes are disposed in a geometric array that is congruent to the geometric array of said operating axes.