Castrol TranSynd 668 is a premium, full-synthetic automatic transmission fluid specifically formulated for Allison Transmission® on-highway automatic transmissions. TranSynd 668 provides oxidative stability, anti-wear performance, and friction durability, as well as TES 668™ specification differentiators such as extended anti-shudder durability and extended clutch friction durability. This fluid features an Allison TES 668 approval. The TES 668 spec is fully backwards compatible for TES 295® applications, but is not backwards compatible for TES 468™ applications.