Allison Transmission and Castrol Industrial North America have teamed up to offer a new synthetic automatic transmission fluid specially formulated for heavy duty automatic transmissions. The new product is called TRANSYND™1 and is approved for use in all current transmission models in all current truck and bus applications.Allison's worldwide customers now have a new option when selecting transmission fluid. Customers may continue to choose from a wide variety of approved DEXRON®-III or Allison C4 quality fluids or they may elect to switch to TRANSYND™ and extend drain intervals. TRANSYND™ has been shown to be cost effective by reducing maintenance through extended drain intervals while providing superior performance. Benefits may be optimized in severe vocations such as transit fleets where there are more vehicles and fluid change intervals tend to be more frequent. Similar savings may also be achievable in general (lighter) duty vocations such as school buses, motor homes, etc. Life Cycle Cost analysis software has been developed to evaluate potential savings based on a customer's individual operating conditions and maintenance practices.Testing at all levels has demonstrated the superior performance of TRANSYND™ in the most severe duty environments. Extended drain intervals have been validated through fleet testing in severe duty applications. This paper discusses the rationale behind the launch of TRANSYND™, reviews the results of various bench, transmission, and fleet validation tests, and discusses the benefits of using this new product in Allison transmissions.