Cummins Diesel and the 68RFE: Why Diesel Owners Need More Frequent Trans Services Than They Think

Cummins diesel Ram owners are a confident group. They believe their trucks are built to handle everything, and in terms of the engine, they're largely right — the 6.7L Cummins is a durable powerplant. But that confidence doesn't always extend to the 68RFE sitting behind it, and the mismatch between what that engine produces and what that transmission was originally designed to handle is exactly why these transmissions fail at the rates they do. The 6.7L Cummins produces peak torque at a very low RPM — typically 1,600 to 1,700 RPM in stock form. That low-RPM torque delivery is hard on automatic transmissions because the torque converter is at relatively low multiplication ratio at those engine speeds, which means the transmission is receiving high input torque with less hydraulic cushioning than it would see from a gasoline engine at the same output torque. The 68RFE's clutch pack apply pressures were calibrated with some margin for this, but that margin erodes fast with fluid degradation and high ambient temperatures.

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