The 48RE four-speed automatic transmission represents an evolution of the previous 47RE transmission model and can be found combined with the Cummins Turbodiesel in Ram pickups from 2003 to 2007 model years. The 48RE transmission design is both heavier and stronger than the 47RE, although the two transmissions share identical ratios. Although the 48RE is considered a significant improvement over its predecessor, it quickly became outdated as power ratings for the Cummins Turbodiesel surged to over 600lb-ft by 2007, the last model year of the 5.9L Cummins ISB. Chrysler would ultimately replace the 48RE transmission with its first diesel specific transmission platform, the 68RFE, following the development of the 6.7L Cummins.
The 48RE transmission features four shift schedules, technically known as governor pressure curves. Governor pressure is electronically controlled relative to engine speed and is used to command upshifts and downshifts according to engine speed and load. The four schedules are as follows:
- When transmission fluid temperature is at or below 30° F – Shifts are delayed and the engine is allowed to rev higher to help the engine and transmission reach normal operating temperature in less time. Shifts are typically harsh while this schedule is in effect.
- When transmission fluid temperature is at or above 50° F – The transmission’s normal adaptive shift strategy is in effect. The adaptive strategy is a dynamic shift schedule that commands upshifts and downshifts based on various operating conditions, including engine speed and load.
- With “wide open throttle” – At full throttle, upshifts are originally commanded by the PCM at predetermined optimal engine speeds. The PCM perpetually learns and creates an optimal upshift schedule based on the time required to complete a shift at a given engine speed/load compared to the desired preprogrammed values. The wide open throttle shift schedule is therefore adjusted routinely based on the outcome of transmission shift events.
- When transfer case 4WD low engaged – In order to compensate for inherent accelerator pedal sensitivity in low range (resulting from significantly higher engine torque multiplication through the drivetrain), the PCM will command upshifts much sooner when the transfer case is placed in the lower range.
The transmission also features a “Tow/Haul” setting that can be activated by a shifter-mounted switch. The 48RE’s Tow/Haul function is not necessarily a “smart” function like those found on modern engine/transmission combinations that have integrated exhaust brake technology and vehicle speed management systems. When the Tow/Haul setting on the 48RE is activated, torque converter lockup is engaged and the transmission shift schedule eliminates overdrive (4th gear) upshifts, therefore direct drive (3rd gear) becomes the final available drive gear. Towing significant weight in overdrive is not recommended, as drive wheel torque is reduced and the load placed on the transmission can contribute to a reduced product lifespan.
The 48RE automatic transmission features an actual input torque rating between 560 and 570 lb-ft of torque; whereas, the standard Cummins Turbodiesel peaked at 610 lb-ft by 2005. As a result, the 5.9L Cummins was designed to detune itself when necessary to promote the longevity of the transmission. The engine will produce its peak 610 lb-ft torque, but only in cases where accessory load brings the actual engine torque output into the 570 lb-ft torque range. In all other cases, the engine will detune to roughly 570 lb-ft of torque under full load. The limits of the transmission are quickly realized in the presence of performance enhancing modifications such as electronic tuning devices.
The 48RE transmission is the weakest point on a Dodge Cummins truck. Not only do they fail on trucks with minor upgrades, but even stock vehicles have been known to be too powerful for the transmission to endure its natural lifespan. A heavy duty truck needs parts which can stand up to heavy trailers, stop-and-go commutes to work, or high-horsepower applications. That’s why we might recommend modifying the transmission to make it the strongest and most reliable part of your drivetrain.
Modern diesel performance is still advancing at a radical pace. Current pickup truck engines can make nearly 1,800lb-ft of torque at the wheels yet still be driveable on the street. Getting that much power to the ground; however, is another matter altogether, and virtually every single part in a transmission could be its weak weak link. Make sure you have the right components in your truck, whether you currently have a 48RE automatic transmission or are looking to replace your current system with one of ours.