The Allison MT643R is a fully automatic transmission with integral input retarder that has been designed and developed for the Latin American city bus market. This transmission provides a cost effective manner to integrate secondary braking into an automatic transmission to lower overall life cycle costs for the city bus. It provides the ease of operation of the fully automatic transmission while providing a system that will enhance vehicle braking and safety while saving on brake system repairs - all in one package. The MT643R has a 250 horsepower input retarder which has a two-stage capacity that, in conjunction with the gear multiplication through the drivetrain as the transmission downshifts, allows for tailoring of the retardation performance to very specific duty cycles. This paper will discuss the design, development, and specific product launch of the MT643R into the Latin American marketplace.