The 47RE and 48RE beckon back to the 727 TorqueFlite transmission of the 50’s and 60’s. It is one of the eldest living dinosaurs in the transmission community and despite its many advancements into the future, is simply based on a very old unit. As a result, this brings both blessings and curses; of which we will analyze in this article.
It’s no secret that the 47RE and 48RE transmissions can be prone to countless issues. However, and in benefit, it can also be one of the most capable transmissions once built. It is for this reason that the 47RE/48RE are fertile platforms for creating a long-lasting, high quality transmission.
Note: These are 2 incredibly similar transmissions that are almost identical of one another, hence we will combine them into one publication. They also share a common application chart which is featured below:
Logically, they are not this in factory form. In fact, it is exceedingly probable that your factory 47RE or 48RE will not survive much more than the first 100,000 to 150,000 miles of its life, depending on your use and maintenance.
In short, this is a transmission that was built to suffice the warranty period of the vehicle, and not much more. This leaves tremendous room for aftermarket engineering to take place, and big solutions to big problems to be created.
Do I have a 47RE or a 48RE?
It should first be noted that the 47RE came into existence in 1995 for the 1996 model year, fitting into the 12-Valve Cummins of the time. In 2003, the 47RE was insufficient for the torque of the common-rail motor and hence the 48RE began standardization in the High Output variations of this motor. Production with the 48RE Carried until late 2007, where it was changed in lockstep with the 5.9L motor for the larger 6.7L motor and adaptive 68RFE (See below) or AS68RC transmissions.
For customers with a 2003 who are unsure of which they have, they can use either of the two methods below:
- Reference your VIN number, if the 8th digit is a 6, it’s a 47RE. If it’s a C, it’s a 48RE. This number recognizes the difference between a Standard Output and a High Output, affirming which transmission the truck would have in most cases. One should visually inspect as well to be most confident.
- Alternatively and as mentioned above, perform a visual inspection. A 47RE featured a 3-Prong Neutral Safety Switch whereas the 48RE featured a 5-Prong Neutral Safety Switch. This is the transmission sensor on the driver side closest to the bell housing.
What are the differences between the two?
The differences between the two are primarily in geartrain and hydraulics. Parts like servos, accumulators, pans and shafts are not different. However, later model 48RE’s has more robust 6-Pinion Planetaries that were made of steal, as opposed to the aluminum 4 or 5-Pinion units of the past.
Also, some of the valve body’s oil geometry was modified when transitioning from the 47RE to 48RE, primarily because of the computerization of shift scheduling in the 48RE. The 47RE shifted based on automated pressure readings and was simpler to control.
It is for this that any 48RE being built as a “Full Manual Valve Body” configuration must use a 47RE Valve Body or earlier as the core. The 48RE does not possess the proper oil configuration to facilitate manual shift behavior correctly.
Lastly, the torque converters internal structure is different, having an additional sealing ring in place in the 48RE. It should be noted that a 48RE converter will drop in and function on a 47RE directly, but NOT the other way around. That stated, we will now address the problems that these two archaic transmissions possess as well as practical solutions to resolve their inferiorities.
Problem #1 - The Torque Converter
The 47RE and 48RE have a virtually identical torque converter; suffering from the same benefits and ailments as one another. In short, this torque converter suffers from multiple different inefficient design flaws that contribute to probable failure early in their life.
One is stall speed, the stall speed of this torque converter is too high for most. In fact, about 80% of the torque converters we sell for the 47RE and 48RE are lower than factory stall speed. It’s simply what most people prefer after doing their research, or talking to a buddy.
Note: Need more info on torque converter stall and how it effects transmission behavior? Check out our Transmissions 101 on Torque Multiplication Factors and how to calculate yours!
Stall speed is controlled by the stator, a critical part of the turbine system found inside the torque converter. Machining this component down, in effect to open up the fins, brings stall speed down. Doing the opposite, in effect to add resistance as oil attempts to travel through the stator under pressure, increases stall speed.
In addition, it simply lacks the surface area necessary to properly engage when commanded and safely sustain the torque of the motor. Naturally, this becomes more dangerous as power or towing capacity grow.
Culminating the converter’s many ailments is a low quality, cast apply piston. We have discovered that this apply piston deflects during application of the converter clutch over time. This makes it imperative that the lockup assembly is comprehensively upgraded during this process.
Products like our “Formula One” 48RE Billet Triple Disk Torque Converter encompass all of these upgrades and more, in one and are excellent options for someone seeking to upgrade their torque converter for any application.
Problem #2 - The Oil Pump
Both of these transmissions have a mostly common oil pump design. Although these 2-Gear oil pump designs are generally reliable, they are prone to some complications. These pump gears are made of a rather soft metal that tends to wear excessively over time.
When it does, the transmission begins to lose pressure at its highest point. Alternatively, the pump is often salvageable during the rebuild process and simply needs basic remanufacturing and placement of basic updates in most cases.
Occasionally, the oil pump will disproportionately accumulate pressure on one side, pushing the gear towards the opposite side. Once this happens, wear is accelerated and oil reversion at high pressure begins.
Problem #3 - The Input Shaft
The 47RE and 48RE input shaft are identical, although the stator support of the pump is different. The input shaft however, likes to fail in excess of 500HP or when frequently used for boosted launches and early lockup’s.
There are multiple different options for a billet input shaft. For most up to 1000HP, a 300M Billet Input Shaft is ample. For above and beyond, AERMET is about 35% greater in tensility and yield.
Alternatively, the Santjer Performance Development Input Shaft and Stator Support is best for those seeking immense power levels. Another common alternative is the 47 Spline “Fat” Input Shaft.
These Input Shafts are modeled off the 68RFE and are convex in shape, creating a bottleneck of oil as it attempts to exit the converter. The SPD Input Shaft is the only input shaft that is larger than the OEM input shaft while also addressing this critical ailment.
Problem #4 - The Intermediate Shaft
The Intermediate Shaft of these 2 transmission is identical, and rather sturdy. It is generally safe up to about 700HP, but after that, should be replaced with a 300M alternative. 300M Intermediate Shafts tend to be safe reasonably past 1200HP.
For customers seeking an extreme alternative, Maraging Steel is a more advanced metal that can be used in the manufacturing of this shaft, and will hold the highest achievable numbers for this transmission.
Problem #5 - The Output Shaft
The 47RE and 48RE output shafts are massive failure points for those who like to perform boosted launches, and are a must for any “play” build. There are 2 different output shafts available on these transmissions; predicated upon if the transmission is 4WD or 2WD. 2WD output shafts are easier to break due to how long and unsupported they are, but can be made of billet.
Note: Due to how large the 2WD output shaft is, it is more expensive to make from a billet material. In fact, a 2WD Billet Output Shaft is about $900 more.
As for 4WD output shafts, there are 2 options for upgrade. One is for standard sized output shafts, being only 23 spline. This is advantageous for applications in excess of 1000HP and also does not necessitate any transfer case modification.
For peak power capability, 29 spline output shafts modeled after the larger 68RFE output gear hub can be used. This is especially beneficial to 68RFE owners swapping to the 48RE, as it makes the transmission spline directly into the transfer case itself, assuming you have an NV273 transfer case.
Problem #6 - The Valve Body
The 4 speed TorqueFlite’s valve body has changed slightly over the years, but has maintained the majority of its general design structure. There are a few immediate issues with this valve body that present complication for all applications.
First of which, they are incapable of safely producing more than about 170lbs of line pressure safely without producing governor pressure codes. This is because the governor pressure system of this transmission uses control and return voltage as well as a transducer to help coordinate shift dynamics, and when it sees too much governor pressure and cannot properly adjust, it will present a code or “pop” the sensor/transducer.
There are also multiple valve or contact related related leak-points in this valve body that are resolved through machining during the valve body remanufacturing process. There are countless talking points associated with this specific components failure, hence, we would encourage you to watch our High Quality and informative 47RE and 48RE Teardown + Buyer’s Guide video or check out our Formula One Valve Body for the 47RE or 48RE!
Problem #7 - The Bushings
As we’ve made a talking point in the past, “babbitt” material bushings are simply an outdated technology that is linked to poor longevity. Babbitt bushings wear out over time due to their soft and consumable nature. The most responsible and cogent way to upgrade the bushing system of the transmission is to replace them with much stronger Bronze material bushings.
The incentive is that Bronze bushings simply outlive the babbitt material bushing many times to one. For anyone seeking a long-lasting “once and done” upgrade, bronze bushings are imperative. It should be noted that all of our 47RE Rebuild Kits and 48RE Rebuild Kits include Bronze bushings standard, just like our transmissions.
Problem #8 - The Electronics
The 47RE and 48RE are one of the rare scenarios where deviation from the OEM electronics can make sense. The only place this should be considered is the governor pressure system, all other electronics on the unit should be replaced with true OEM replacements for maximum reliability; as is done in all of our built 47RE and 48RE transmissions.
When speaking about deviating from OEM, the 2 electronics designed to be changed as such are the governor pressure sensor and governor pressure transducer. Both of which respond negatively to increases in line pressure and suffer from poor longevity.
A high performance transducer consisting of stronger copper windings that withstand higher voltage more safely is a must, as well as a governor pressure sensor that is up for the job. It is common to convert to the Allison Style Governor Pressure Solenoid. This is a very affordable way to prevent this failure in the future, when coupled with a new transducer. This is also spoken about in our 47RE/48RE video linked above.
Problem #9 - The Intermediate Band
When it comes to longevity, this may be the biggest problem of them all. The OEM 47RE and 48RE band is a very low quality, soft metal with a paper thin friction lining. It’s highly flexible and the only thing keeping the paws for the strut and anchor in place are small little rivets. An OEM banned where the paw had snapped off is pictured below.
Bottom line, not safe. They stretch, until they physically can’t apply anymore, generating poor shift quality into and out of 2nd gear. In fact, it should be noted that you never actually have to adjust this band. If at any point you do, it’s often because the band is out of friction material.
A much more reliable (and expensive) band is the original 727 style rigid band. These bands are dramatically more reliable, up to about 800HP. We prefer this style of band for all applications, but differentiate between 2 different band designs; one for extreme performance, one for stock to high performance and maximum longevity.
A final ailment that should be noted is that when the band runs out of friction material, it begins to eat at the drum. This is similar to how brake shoes will eat the outer brake drum after becoming excessively worn. To prevent this, do not allow an OEM flex-band to exceed 120,000-150,000 miles!
This is an expensive fix and can be easily prevented through timely internal maintenance. Trucks with added power, large tires or rigorous applications can expect to be on the shorter end of that longevity spectrum.
Problem #10 - The L/R Sprag
This is one of the less spoken about issues. The reason you don’t hear about this much, is because it seldom actually breaks in most applications. The customer that breaks a L/R sprag is the customer that has an automatic configuration to their valve body, yet likes to boost launch in first gear.
The logic behind this is that the sprag gyrates in an unsafe fashion that can cause it to crack or come apart. Bolt-In Sprags prevent this concern, and are standard on products like the Race 48RE w/ Formula One Torque Converter. This is because we wholly anticipate customers with products such as that to be using them for their intended purpose, and are built and up-armored accordingly.
Problem #11 - The Filtration
There is tremendous misconception about the market that the earlier 47RE “open” style filter is more reliable than the later metal filter. We have studied this to the furthest of our ability and have found simply no conclusive data to suggest this is true.
In fact, we discovered that the later style metal filter was designed as an update to the older open style filter. Mopar had multiple warranty calls when the 47RE was new that were traced to trucks being on tall inclines or declines and oil was not able to properly travel through the filter due to the location of the sump inside the filter.
Furthermore, the metal filter can “suck” oil much more safely, without presenting the trepidation of cavitation as is logically concerning with the previous design of filter. An updated OEM anti-cavitation filter should be part of any rebuild or valve body swap.
Problem #12 - The Oil Pan
Although not a huge detracting factor, it should be noted that the OEM oil pan is low in volume, dismally weak in strength and contributes to sustained higher operating temperatures; an obvious negative. It is for this that most install an affordable 4 Speed TorqueFlite Deep Pan.
It should be noted that these pans will fit any year of 727 with adequate ground clearance. Most diesel trucks do not mind this, but we must remember that this transmission has been used in countless things since the dawn of time, even the Dodge Viper of it’s time!
Problem #13 - The Lever, Strut and Anchor
The Lever, Strut and Anchor are 3 parts that work in conjunction to apply and release the intermediate band during the appropriate shifts. The issue is that the heavier the truck, and the more line pressure the valve body can capacitate, the more stress these parts experience.
As power levels and trailer weights increase, these can crumble and leave the truck immobilized without internal repair. Needless to say, this is something worth avoiding at all costs. Using a billet lever, strut and anchor is a safe solution to nearly any power level.
Some often ask about the “apply ratio” of the lever. We have studied this and discovered that 5.0 is the only one to avoid, and 4.2/4.4 yield similar results. This number signifies loosely how long the lever is and has a direct impact on shift timing. Many with build transmissions donning the 5.0 ratio lever report a “surge” going into 3rd gear, another reason we do not use 5.0 ratio levers.
Problem #14 - The Servos
The 47RE and 48RE both have 2 servos that full with oil to move apply levers; one is for reverse, one is for the intermediate band. They fail the same way, and henceforth will be included together here.
The intermediate and reverse servo are cast from the lowest quality aluminum possible, and tend to crack under application. Once they crack, they can no longer hold oil, causing a debilitating crossleak that doesn’t allow any oil to generate pressure at the servo. This leaves the corresponding band out of commission, and likely damaged from trying to apply without adequate pressure.
To resolve this, billet servos should be used in place of the inferior OEM servo designs. In addition, there is an update to provide a seal to the intermediate servo shaft, preventing crossleakage at the infamous portion of the servo where the face slides onto the shaft. Being aware of this helps us prevent high mileage 2nd gear failures in our build 47RE and 48RE transmissions.
Problem #15 - The Accumulation System
The 47RE and 48RE both have very straightforward accumulation systems. They bear only one piston for the 3-4 upshift, and one for the 1-2 upshift. The 3-4 piston is smaller and inside the valve body, hiding behind a backing plate. The 1-2 piston is harder to access, residing in the case between both servos.
To absolve the concerns associated with these pistons, it is most logical for one to replace them with billet alternatives. Beyond that, aftermarket pistons feature more/better seals, preventing crossleakage from robbing you of longevity or power capacity. This makes the accumulators a critical part of how the 4 Speed TorqueFlite operates.
Problem #16 - The Flexplate
Flexplates are always a topic of discussion because their purpose is so frequently misunderstood. As the converter rotates at tremendous speed, it generates immense amounts of internal converter pressure. This is why some converters “balloon” under high stress.
The flexplate’s critical task is to absorb this stress by traveling forward and backward in an axial fashion, flexplates that are TOO sturdy to flex take this critical benefit away, relegating the stress to the pump and converter.
Granted, flexplates also break. The solution is not a stock flexplate, nor a 40 pound flying saucer. The solution is a reinforced Steel or Billet SFI approved flexplate, designed for added power without being unnecessarily rigid. At Next Gen, practicality and longevity are every bit as important as the power figure. As a result, understanding advanced concepts like this become critical.
Problem #17 - The Forward Clutch Drum
The forward clutch drum has two primary issues. One is that the clutches are insufficient for most applications, causing it to die prematurely. The other is due to cracking of the aluminum rear clutch retainer.
Resolution of the clutch problem is rather easy, higher quality clutches and steels along with a billet backing plate provide all of the added torque capacity and other safety measures necessary for this clutch pack to succeed.
Cracking of the retainer is a different problem, but to fix it, we must understand why it happens. In first gear, the forward clutch pack begins to rotate at the speed of the motor. Centrifugal inertia is the physical force that now acts against the rear clutch retainer as it spins.
The end result is crackage from the aluminum being too weak to withstand repeated heat cycles and high speed rotation. CNC Machined Billet Steel alternatives such as the Billet 4 Speed TorqueFlite Rear Clutch Retainer are necessary for ultra-high performance applications.
Problem #18 - The Direct Clutch Drum
Failing for different reasons than the forward clutches, direct clutch drums fail due to insufficient clutch capacity and a very weak cast aluminum piston. When the direct drum fills with oil, this aluminum piston (made of the same low quality aluminum as the servos) can crack.
This causes the same type of failure as cracking a servo, or any other oil dam within the transmission. In addition, adding a clutch can be performed very safely by machining down the backing plate and using a slightly shorter apply piston. This yields a notable increase in torque capacity.
Problem #19 - Overdrive Direct
Like other clutch packs, the friction element quality is low, leaving great room for reliability woes in the overdrive direct clutch pack. However, in this clutch pack, there is an added point of contention.
In the Overdrive Direct, the snap-ring that holds the clutch packs backing plate in place likes to break, often being found in the bottom of the pan. This is a considered a catastrophic failure and simply necessitates an entire rebuild whenever seen.
These pieces of snap ring can find their way into gears, orifices and more. A thickened updated snap ring removes this concern and keeps the clutch pack safely in place for years to come. This can be a daunting failure because the transmission will often continue to run after this specific failure presents, making it hard to identify until it’s too late for many, as can be seen below.
Problem #20 - Overdrive Brake
The previous clutch packs of the 47RE and 48RE have had common issues with insufficient clutch capacity or clutch quality, and Overdrive Brake is not different. This clutch pack tends to burn itself out in upper gears due to this.
Replacing these clutches and steels with aftermarket upgraded alternatives is generally all that needs to take place here, aside from proper remanufacturing practices. High quality clutches will survive most power levels in this part of the transmission with minimal concern.
The 47RE and 48RE were never originally designed to be used in large diesel trucks, but rather inflated to “make it work.” As a result, we were left with transmissions that simply could not safely capacitate the goals of the market. But, all hope is not lost for this unit.
In fact, with adequate investment, time and understanding, the 4 Speed TorqueFlite can be one of the most reliable transmissions on the market. If you have any further questions about upgrading your unit or building the right transmission for you, click here or call in and speak to one of our experts!