Detroit DT12
The other half of the Freightliner fuel economy story. Paired with a DD15 and a downsped axle it is the drivetrain most fleet fuel testing puts at the top, and eCoast, which freewheels on downgrades, is the feature people notice.
Torque rating
1650-2050
pound-feet at the input
Weight
700 lb
60 lb over the lightest, which is payload
Shifting
Actuated
software decides the gear
Maker
Detroit
What it does to fuel
Among the best available, and the integration is the reason: engine, gearbox and axle are calibrated as one set rather than three parts that happen to be bolted together.
What this type is
The same gearbox with the clutch and the shifting actuated. It is NOT an automatic, it has no torque converter, and it fails and gets repaired like a manual. This is now the default in new linehaul, because software shifts more consistently than a person and consistency is fuel.
Known issues
Clutch actuator and shift rail sensors. It is a manual underneath, so a worn clutch is a clutch job rather than a rebuild.
Verdict
Buy the whole Detroit drivetrain or do not bother. Mixing a DT12 with another maker's engine gives up most of what you are paying for.