We all know when it comes to a tow vehicle, nothing can compare to Dodge's powerful line of Ram pickups. Dodge set the standard when they developed this platform, and then raised the bar when they installed the potent and efficient Cummins turbo diesel and brutal V-10 for class-leading power. Ask any owner of one of these trucks and the only complaint you'll hear is, "Dodge trucks are great, but they need a transmission that will harness the power." Yes, the transmission has long been considered the weak link in a Cummins or V-10-powered truck, but is the transmission really to blame? The 47RE automatic gearbox and its variants used in these trucks are direct descendants of the tough 727 TorqueFlite, which is known for its strength and longevity. Heck, with minor modifications we've seen TorqueFlites handle upwards of 1,000 hp at the racetrack, so how can the modern version be so weak? The fact is the Dodge's transmission is as strong as any we've seen and has been the scapegoat for the drivetrain's real weak link-factory lock-up torque converter.
In the '70s, Chrysler introduced lock-up-style torque converters as an inexpensive way to improve the efficiency of their vehicles. As a fluid coupler, the torque converter is a compromise between slippage, allowing the car to idle in gear, and efficiency, transferring as much of the engine's power as possible to the transmission to propel the vehicle, even multiplying torque at lower rpm to help launch the vehicle. Without seeing the inside of a torque converter you can still understand its basic operation by performing a simple experiment. Place two electric fans facing each other about six inches apart. Now plug in one of the fans and turn it on, this fan represents the driving fan inside the converter that is connected to the engine's crankshaft. The other fan represents the driven fan inside the converter that is connected to the input shaft of the transmission. By varying the speed and proximity of the fan that is plugged in, the other fan will spin, but never as fast as the fan that is plugged in. Substitute transmission fluid for air and contain it in a steel housing, and you have a crude version of the fluid coupler called a torque converter. Using converter terminology, we call the fans the impeller and the turbine, and in a converter, unlike our fan simulation, these are separated by a stator, which directs the fluid from the impeller to the turbine and keeps fluid from flowing opposite the designed direction. By varying the pitch of the blades inside the converter, you can vary the rpm that the converter starts pulling and vary the efficiency of the converter, but the only way to get both sides of the converter to spin at the same rpm is by the use of an internal lock-up clutch.
The lock-up clutch, while improving the efficiency of moderately powered vehicles, is the downfall of your Cummins or V-10-powered truck's transmission. The lock-up clutch is inside the converter itself, and the factory piece is a single disc that is normally engaged and hydraulically disengaged by fluid pressure from the transmission. The problem with the factory unit is it doesn't have the holding power required to harness the torque of a powerful diesel or V-10. When under a load, the lock-up clutch slips, creating heat and glazing the clutch and its mating surfaces. Once glazed, the lock-up clutch has no hope of holding and will slip and chatter, only getting worse over time. Continued use, especially in vehicles modified to make more power or used for towing, will cause the clutch to self-destruct, sending pieces of clutch disc through the transmission often damaging the internals in the process. Centrifugal force can also cause pieces of the disintegrating clutch to migrate to the outer limits of the inside of the converter, causing vibrations due to the ensuing out-of-balance condition. Our Cummins-powered Dodge 3500 showed all the signs of lock-up clutch failure, chattering when power was applied or when towing, especially up hills, and heating the transmission fluid to the point of fluid break down. Using our truck for towing and the addition of such power-adding equipment as an Edge computer, wastegate controller, and free flowing exhaust no doubt accelerated our problem. Prior to the addition of our next power adder-digital propane injection-our converter had to be changed.