Common Problems: Cummins 47RE

January 2018 Tech Corner, Feature Colin Peterson

If you own a 1994-2002 12- or 24-valve Cummins-powered RAM truck and have had automatic transmission problems, you’re most definitely not alone. The 47RE transmission in these trucks is not a favored transmission among Cummins owners. Some of the most common problems with this transmission involve being stuck in a gear, failure of the torque converter to lock, or hard shifts. These problems are known to make successful mods to this transmission nearly impossible. That is largely due to the small size of the transmission’s shafts, clutches, and converter; they’re all considerably smaller than those on the competing GM (Allison) and Ford Super Duty transmissions. The 47RE also uses an older design on its components that existed before the transmission was introduced. That’s not like Ford and GM transmissions, which had entirely new designs implemented. The 47RE uses bands to shift gears as opposed to clutch packs.

To get a stronger idea of the common problems in this transmission, we talked with Brent Willsey, owner of PowerTech Diesel, located in our home base of Idaho Falls, Idaho. We also interviewed William Terry of Cedar City, Utah-based performance transmission shop Power Driven Diesel. According to Willsey, “All of the components are just really out of date for the stuff this transmission is meant to do.”

Up Close & Personal

One prime example of a truck with a multitude of 47RE problems is a 2001 24-valve RAM owned by Taylor Fisk. That truck has since had its old RE replaced by an in-house rebuilt 47RE from Power Driven Diesel (which also manufactures its own line of transmission fluid) and a torque converter from Diesel Performance Converters (DPC). PowerTech Diesel collected the major components from those manufacturers and did the meat of the work on Fisk’s truck, which came into the shop barely operable. The Idaho Falls shop didn’t bother to fix the old transmission, as Fisk wants to put more mods on his truck, and the 47RE isn’t a safe modifiable transmission.

“His transmission was surging and slipping with many other things wrong with it,” says Willsey. “We also replaced his converter because it was stuck. The stock converter has a single disc design; it’s not recommended for pulling so many heavy loads.”

The DPC converter that’s now on his truck has a triple-disc design, which provides a more powerful clamping force and features a billet lid, making it very efficient and much better suited for frequent heavy hauling and performance boosts.

Why Can’t the 47RE Hold More Power?

The main reason the Dodge heavy-duty four-speed automatics don’t do well with more power is their low hydraulic line pressure, which actuates the bands in the transmission. This pressure problem can be solved, though, by the installation of a performance valve body or shift kit, a pan-off upgrade that involves removal of the valve body and installation of new internal components to increase pressure and improve shift firmness. That’s exactly what Power Driven Diesel and PowerTech Diesel did to Fisk’s truck.

“The problem with most shift kits is they do not allow much more than a 25 to 30 percent increase in line pressure, which equates to a similar 25 to 30 percent increase in power-holding capacity at the transmission itself, but just a small 10 to 15 percent increase in power holding capacity at the torque converter lockup clutch assembly,” explained Terry from Power Driven Diesel. “Performance valve bodies can raise the line pressure even more, but there are several internal transmission components that should be upgraded from factory cast to billet aftermarket parts when line pressure exceeds 50 percent over stock levels.”

A stock 47RE will only safely handle 100psi of fluid pressure, while a Racing Valve body from Power Driven Diesel can handle 225 to 250psi, and thus more than 1,200 horsepower output.

Common Problem #1: Solenoid & Sensor

“Generally when truck owners complain of the truck getting stuck in first gear in 47RE electronic controlled transmissions, there is an electrical problem in the valve body with the governor pressure solenoid,” says Terry.

The solenoid rapidly energizes and de-energizes to create governor pressure, while the transducer sends feedback to the powertrain control module (PCM) on governor fluid pressure and fluid temperature. When the transducer fails, it sends the wrong voltage to the PCM, and the solenoid will not be properly energized and will result in low governor pressure, in turn resulting in upshift failure. When the solenoid itself fails, it also produces the wrong fluid pressure; this can leave the truck stuck in third gear full-time (limp mode), will only allow second gear starts, and can delay shifts in cold weather or prevent upshifts altogether. Thankfully, though, replacement of the solenoid and sensor doesn’t require involved disassembly of the transmission.

A replacement solenoid that’s better designed for performance boosts is available from BorgWarner. With the pan off, pull off the lower part of the body (which contains the transducer) and then, using a small prying tool, pull off the clip holding the transducer. Insert the new transducer and reinsert the clip. Next, replace the solenoid, which simply pops out upon pushing it. Unplug it, plug the new one in, and move the new solenoid in place of the old one. When that is done, put the lower part of the body back on.

Common Problem #2: Front Transmission Band

Another common 47RE problem is a loose band on the front planetary gear set (which controls shifts into and out of second gear), which causes delayed shifts from first to second gear, and also from second into third. A hydraulic servo pushes the band to tighten it in the process of selecting the next gear. Unfortunately, the 47RE transmission has a very sensitive band that cannot withstand any wear. In turn, when the adjacent screw is misadjusted, the band can be too tight or too loose. A tight band wears away more quickly and gains clearance around the gear set, eventually making the band too loose for the next gear to engage and causing the transmission to slip. An already slightly loose band causes the anchor piece to fall out, exacerbating the problem. Band slippage happens especially when applying a bigger burst of throttle, as the gear set spins faster and makes engagement of the loose band more difficult. This problem can be serious, as when you need to accelerate quickly, your natural instinct is to apply more throttle pressure. To best prevent these problems from occurring, it is important to take off the transmission pan and valve body every 24,000 miles or 24 months (whichever comes first) and check the adjustment of the screw, held by a nut on the exterior. The nut should be adjusted to 72 inch-pounds and backed off a 1 7/8-inch turn.

Common Problem #3: Poor Electrical Connections

Aside from delayed shifts in certain gears, the 47RE is even known to hop around sporadically to different gears, and its torque converter is known to jump in and out of lockup (the point where the engine and transmission settle on the more “constant” speed after accelerating). This is due to poor electrical connections to the PCM and interference from other electrical components under the hood. One notorious source of lockup failure is the main ground wire to the PCM, which faces interference from the alternator as the wire runs near it. The factory material on the wire isn’t thick enough to shield electromagnetic interference, thus what happens is that the PCM picks up on the alternator and distributes the wrong voltage to the transmission solenoids. The PCM then confuses itself and keeps trying to shift to a higher gear when it has already gone through all of them. At that point, the converter can only go into lockup. This problem can be an easy fix, though. To fix it, grab some sheets of aluminum foil, cut them into smaller pieces, and wrap them around the ground wire with electrical tape. The ground wire can be identified by its black shield with a yellow stripe. When done, pull the ground wire back out of the way of the alternator.

“Another way to fix this problem is to re-ground the alternator,” adds Willsey.

Conclusion

So we can very clearly see now why the Dodge 47RE transmission is not the ideal choice for truck owners. It has a very touchy design that can’t take any engine performance boost well. Many mechanical components (such as the bands) are too weak, the stock electrical components fail frequently, and the complex electronic systems confuse the transmission when slight electrical interference occurs. Even as a stock transmission on a stock truck with no mods, the transmission is touchy to maintain. It is important to stay on top of the maintenance schedule and adjust the band on time to avoid problems with it. Even if it seems the governor pressure solenoid and transducer don’t need replacement, if you need to take the transmission pan off for any other reason, always change the electrical devices anyway. More importantly, if you truly feel the need to add any performance mods your 1994-2002 Cummins, by all means, always buy an in-house rebuild from a shop like Power Driven Diesel.

Sources

BorgWarner

248-754-9200

www.borgwarner.com


Diesel Performance Converters

770-318-8696

www.dieselperformanceconverters.com


Power Driven Diesel

435-962-9555

www.powerdrivendiesel.com


PowerTech Diesel

208-261-2304

www.powerlabsdiesel.com

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