Chrysler RFE

Jan. 2, 2014
Chrysler’s family of RFE transmissions began as a 4-speed and currently is a 6-speed transmission. The RFE means it is a rear wheel drive, fully electronic transmission. 

Chrysler’s family of RFE transmissions began as a 4-speed and currently is a 6-speed transmission. The RFE means it is a rear wheel drive, fully electronic transmission.

In 1999, the 4-speed version called the 45RFE was put into the Jeep Grand Cherokee 4.7L vehicles followed by Dodge Dakota and Durango 4.7L in 2000. By 2002, it found its way into Jeep Liberty and Dodge Ram 1500.

With slight changes to some internal parts and programming, the design of the transmission allowed for it to easily become a 5-speed and was called the 545RFE transmission. This occurred as early as 2001 in Jeep Grand Cherokees.

To handle increased torque demands for later model diesel applications, internal components were modified, gear ratios and shift strategies were changed to produce a 6-speed version of this transmission called the 68RFE. The 2007 Ram 2500 and 3500 full chassis pickups with the 6.7L Cummins Diesels were the first to receive this 6-speed transmission.

In 2012 the 545RFE transmission was recalibrated to provide six speeds in the Electronic Range Select mode only. In the normal drive range, it will shift as a 5-speed unit. In Dodge Ram 1500 models, this transmission is referred to as a 65RFE. In 2500 and 3500 gas models, it is called the 66RFE. Some improvements were made to the torque converter with these two transmissions as well.

Regardless of whether it is a 4-, 5- or 6-speed transmission, all of them utilize the same six clutch pack assemblies: three that drive the gear train, three that hold and one low sprag.

As with any automatic transmission, there are times where it would be quite helpful to check clutch pressures in a diagnostic approach to a problem. This step, however, is often time bypassed for one reason or another. Legitimately, once installed into the vehicle, the taps on various transmissions become inaccessible. In some instances, the time it takes to make those taps accessible the transmission is near out of the car. Sometimes these taps are only inches away from the catalytic converter.

With Chrysler’s RFE transmissions, all the clutch pressure taps have been placed on the valve body itself. This requires having a special pan with access ports and pressure pipes fittings (Miller Special Tool 8258A) to reach those taps with which to attach gages to.

Removing the pan, the pressure taps, installing the special service pan, then the pressure pipe fittings, gauges and fluid is without a doubt a time-consuming process. As a result, I know only a few shops that have made this investment. So clutch pressure rarely is ever checked.

Checking main line pressure is another challenge with this transmission as well. In fact, there really is not a dedicated line pressure tap on this transmission. What it does have is an external line pressure sensor (transducer) located on the right rear side of the case.

As with any transducer used on or in a transmission, it reports back to the computer the pressures it is monitoring; in this case (or should I say “on this case”), main line pressure. 

The parameter display provided to the scan tool from the computer for this transducer is referred to as “Actual” line pressure and can usually be observed in volts DC or pressure psi. The “Desired” line pressure parameter is what the computer is commanding line pressure to be based on load and temperature and other pre-determined factors. This parameter can be viewed in psi as well as duty cycle percent.

With line pressure being sent to the transducer for it to be monitored, it’s a great place to be able to check line pressure with a gauge. Although the transducer is supposed to be monitoring line pressure, and the scan tool calls it “Actual” line pressure, this doesn’t mean it’s true. A pressure gauge on the port will tell you if the transducer is working correctly or not.

Attaching a pressure gauge to this port however requires a special tool (Miller Special Tool 8259). The transducer is removed from the transmission and the tool installs into the port. A mounting block at the end of the hydraulic line of the tool provides a location for the transducer to be installed as well as a pressure gauge. This allows the transducer to remain plugged in both electrically and hydraulically. If it remained unplugged, a code would set and line pressure would remain elevated.

When all things are working correctly, desired and actual pressure readings in the scan tool are usually within 3 psi of each other. Here are typical readings taken from a good working 2007 Dodge Ram Truck (4WD) 5.7L V-8:

Idle in Drive stopped

Actual Line Pressure 1 (PSI)_________________    38.1

Desired Line Pressure (PSI)_________________      40.0

Line Pressure Duty-Cycle (RFE) (%)___________ 29.1

Stall in Drive stopped

Actual Line Pressure 1 (PSI)_________________    157.8

Desired Line Pressure (PSI)_________________      160.1

Line Pressure Duty-Cycle (RFE) (%)___________  5.1

Medium acceleration

Actual Line Pressure 1 (PSI)_________________    118.0

Desired Line Pressure (PSI)_________________      118.0

Line Pressure Duty-Cycle (RFE) (%)___________  19.67

Cruising in 5th with TCC On

Actual Line Pressure 1 (PSI)_________________    77.0

Desired Line Pressure (PSI)_________________      77.0

Line Pressure Duty-Cycle (RFE) (%)___________ 22.67

With a special service tool being required to check line pressure, this diagnostic check is often times never performed causing unnecessary guesswork that equates in wasted time and money. The danger here is there have been times where we have seen transducer data matching the desired command when in actuality it is not. You could discover this only by matching the data from a scan tool with a real pressure gauge.

When the transducer fails yet matches the desired command, the result has been repeated Overdrive Clutch failure. With other common reasons for Overdrive Clutch failure (such as a worn bore with the solenoid switch valve line up in the valve body), combined with not having the special tool, line pressure is never checked to see if the transducer is faulty. Eventually the sensor gets replaced and the problem is resolved.

The upside is this pressure transducer usually works well, and when it does, it can be used to diagnose other issues. For example, when cold, the desired and actual pressure readings match but when it warms up, baseline pressure drops. At idle, the desired pressure command shows 40 psi yet actual says 25. As soon as you step into the throttle, actual sensor readings ramps up immediately and match the desired command. This is indicative of a worn pump.

If transducer data (actual) is lower than desired when cold at an idle but begins to match as it warms up, a defective or substandard filter usually is the cause. When it fails badly, actual never matches desired.

There have been occasions when substandard filters became loose in the filter to pump seal. This allows the pump to suck in excessive air causing the actual data in the scan tool to fluctuate erratically.

Speaking about a worn pump, these pumps contain the primary pressure regulator valve and all the valves related to converter clutch control.

One of the common problems with this pump is with the springs breaking. Another is severe bore wear with the Torque Converter Clutch Limit Valve. We have seen this to occur frequently with 2005 to 2007 models. The typical complaint that accompanies wear in this area is a stalling of the engine when it is placed into gear. This is due to a lack of converter charge pressure, which is used in part to push the clutch away from the cover. With a lack of charge (release) pressure, the clutch makes contact with the cover. When the transmission is placed into gear, it will act as if you didn’t depress clutch as with a manual shift transmission.

Both the converter clutch apply and release pressure can be inspected with a pressure gauge without the use of any special tools. The two taps are located on the right side of the transmission behind the converter housing and between the cooling lines. The upper tap is TCC Release Pressure while the lower is the apply pressure. When driving the vehicle, apply pressure can range between 15 to 80 psi, while release pressure can be between 35 and 118 psi. Once the converter clutch is commanded fully on, release pressure should drop to zero psi.

Beware the first time you ever handle a 68RFE converter. Not only does it have several notable differences in design from the 545RFE, it’s heavy. At around 65 pounds, it is one of the heaviest converters in the industry. Interestingly enough, this beefy converter is only supported by a pilot in the crank shaft and the inner pump gear through the converter’s impeller hub. So a well fitting pilot is critical with this set up. 

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