Dodge / Ram
by Michael Dickens
In June 1998, Chrysler introduced the innovative 45RFE in its 1999 WJ Jeep Grand Cherokee. Produced at Chrysler's Indiana Transmission plant in Kokomo, it was paired with the 4.7 L PowerTech V8 engine. The 45 number refers to the torque rating (5) and number of forward gears (4); RFE refers to rear wheel drive application and full electronic controls.
The 45RFE automatic transmission had three planetary gear sets instead of the two usually used in a 4-speed automatic (which would, in time, allow it to become a six-speed). It included three multiple disc input clutches, three multiple disc holding clutches, and a dual internal filter system, one which was a primary filter for transmission sump, the other for the fluid cooler return system.
Four forward gears were used in normal acceleration, with a different second gear used for “kickdown” acceleration. Despite using five forward ratios, Chrysler played it safe and decided to call it a "4-speed automatic."
The 545RFE’s engineering reached back to the rock-solid Torqueflites, but it incorporated many contemporary innovations and practices.
At the time, Chrysler boasted of its tall 3.00:1 first gear for initial acceleration; and noted that while the standard second gear was 1.67:1, the kickdown second was 1.50:1, for smoother downshifts. Reverse gear was equal to the first gear to accommodate heavy loads. At the time it was launched, it had the widest range of gear ratios in its class; and its factory was brand new at launch.
In 2001, with programming changes and an extra, taller overdrive ratio, the 545RFE was born. With the change to overdrive, cruising at 70 miles per hour (110 km/h) with a standard axle ratio would yield 2000 rpm at the engine, about 200 rpm less than the 45RFE, cutting fuel use and noise. Now, it had six forward speeds — again, one reserved for kickdowns.
As to the question of why the 545RFE has two overdrive gears that are so close to each other, engineer Bob Sheaves noted that size is an issue with planetary gears; most likely, the top 0.67:1 ratio gear was chosen because that was the largest one that could fit without making the transmission too large for the vehicles it was in.
When towing (in some vehicles), a “Tow/Haul” mode made faster shifts to cut wear on the transmission, and reduced gear searching by holding lower gears longer, also choosing lower gears when going downhill to increase engine braking.
In 2006, Chrysler claimed that the transmission had been “refined for higher-quality shifts;” it was strong enough to give the Jeep Commander and Grand Cherokee class-leading towing capacity of 7,200 lbs. The changes included a redesigned solenoid for quieter shifting (ending “solenoid clatter”), and a turbine damper to cut noise and vibration from the torque converter.
Used in Chrysler's fleet of rear-wheel drive trucks, including the Jeep Liberty, Dodge Ram, Dodge Dakota, Dodge Durango, and Jeep Commander, the computer controlled 545RFE was kept in a shiny, one-piece die-cast aluminum casing. Ribs in the case increased torsional rigidity. An internal lubricant filter was for the main sump pan, and an external filter was for the pump return. It took 6.2 liters (6.6 quarters) of ATF+4 fluid; early units could take ATF+3.
Critics sometimes complain about the choice of gear ratios, which is aimed at providing reserve torque. The transmission was well suited for the large torque band of the Hemi V8, 3.7 V6, 4.7 V8, and VM 2.8 diesel.
In 2009, the computer was programmed to let drivers select the highest gear the transmission would shift to, for easier towing, hill climbing, and hill descent.
In 2012, Chrysler launched three new six-speeds, all based on the 545RFE.
First out of the gate was the 68RFE, a heavier-duty automatic created essentially by using a similar clutch and hydraulic control system, with different planetary gears and tooth counts. Numerous parts, including the various shafts and clutches, gears, and the torque converter, were redesigned to handle the high torque of the Cummins 6.7 liter diesel. Pump capacity was increased to deal with heat more effectively.
Designed to work with the Cummins engine, the 68RFE has a lower first gear than the 545 for better launches, giving it a wider spread of ratios. The torque converter clutch is engaged in every forward gear but first, based on factors such as temperature, gear, tow/haul mode, exhaust brake activation, etc. The transmission was designed to include electronic range selection. Because it uses a unique computer, it cannot be retrofitted back into earlier trucks. The assembly weighs 263 lb.
The next six speed derived from the 545RFE was the 65RFE, used with V8 versions of the Ram 1500, Durango, and Grand Cherokee. The 65RFE only has six forward gears in ERS/AutoStick mode or kickdown mode; it is essentially a software and name change, which allows people to reach the “prime” gear via ERS as well as than kickdown. An internal Chrysler communiqué to dealers summarized the change in a similar fashion.
The 66RFE is a new transmission based on the same basic core as the 545RFE. It is similar to the 68RFE in basic construction, but differs in duty rating; for some of the possible differences, see the 68RFE page. Gearing is identical to the 68RFE.
* On 545RFE, 3rd is only accessible via kickdown in some situations, and is referred to as “2 prime.” On 65RFE, 3rd is only accessible via kickdown in some situations and use of manual override.** Chrysler specified a 2.21:1 reverse gear in some applications, including the Jeep Liberty diesel.
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