Allison has 2 transmission that are used in Newell type vehicles. The older HT740/750 is a 4/5 speed unit. Top gear is one to one & the lower gears have a multitude of ratio's available depending on the application. Some 5 speeds actually start out in second unless overridden. The later transmission, the World transmission comes in may variations, but for high end coaches, the HD4000/4060 are popular. Most are 6 speeds with 5 & 6 being overdrives. These units can handle almost all the larger 4 stroke engines available today. The 4 stroke's are much happier @ a lower RPM than the old 2 strokes.
You can use the link below to find out specific data on later models
http://www.allisontransmission.com/m...tion/index.jsp