The 68RFE and 66RFE automatic transmissions for Ram trucks
In 1998, Chrysler launched the 45RFE transmission, which used three planetary gear sets instead of the two usually used in a 4-speed automatic. This evolved into the 545RFE, and then the 68RFE, launched in 2007, and the 66RFE, a lighter-duty version of the 68RFE launched in 2012 (the main differences are reportedly in the torque converter).
The 68RFE, a six-speed automatic, was based on the 545RFE, using a similar clutch and hydraulic control system, but changing to heavier duty planetary gears with different tooth counts. Numerous parts, including the shafts, clutches, and torque converter, were redesigned to handle the torque of the Cummins 6.7 liter diesel; pump capacity was likewise increased.
|Reverse||3.00 or 2.21||3.54||4.445|
The 68RFE has roughly the same torque capacity as the Aisin automatic in other Ram heavy duty pickups, but the Aisin allows for a power takeoff (PTO) and the 68RFE does not. The Aisin AS68RC also has a steeper first gear for better off the line power, with the same sixth gear ratio. (The Getrag six speed manual available on these trucks had a 5.94:1 first gear and 0.74 sixth).
A “Tow/Haul” mode provided faster, crisper shifts to cut wear on the transmission. Under partial throttle, shifting into gears above third was delayed; and the system was likely to kick down under part throttle into fourth and fifth.) The Tow/Haul mode still allowed overdrive unless the driver locked it out.
Gear ratios were designed to maintain speed on long or high grades, without sacrificing efficiency at highway speeds. Unlike the 545RFE, it uses all six gears in normal acceleration; the 545RFE had a sixth forward gear used only for kickdown.
Electronic Range Select let drivers limit the highest gear. In the Ram Heavy Duty, a +/- switch was on the column shifter. The gear showed in the gauge cluster. This is mostly useful for towing and downhill or long uphill runs. Allpar’s test drive commended the transmission (in 2010) for rapid kickdowns and general responsiveness.
The torque converter clutch is engaged in every forward gear but first, based on factors such as temperature, gear, tow/haul mode, and exhaust brake activation. Because it uses a unique computer, it cannot be retrofitted back into earlier trucks. The assembly weighs 263 lb.
Owners have pointed to weak spots in the transmission, as made from 2007-2011, particularly the torque converter. Partly for that reason, in 2012, when Ram started selling a higher-output Cummins diesel truck (with 800 lb-ft of torque), they beefed up the torque converter and modified the shift algorithms for durability.
The 66RFE and 68RFE provide a wider overall gear range than the 545RFE/65RFE. A label on the transmission case has the part number and build sequence (which are also stamped into the case, below the label). The 66 and 68 have one set of splines on the overdrive shaft; the 545/65 has two.
The 66RFE resembles the 545RFE from the outside, but share sits extension housing and output shaft with the 68RFE. The 66RFE has its torque converter recessed inside the case, while it sticks out of the 68RFE.
All three automatics have a one-piece case, electronic control, two stage hydraulic pump (which shuts the secondary side at higher speeds, for efficiency), and similar valve bodies. They all use three planetary gearsets, three driving clutches, three holding clutches, and an overrunning clutch. The 66 uses some parts derived or taken from the 545 (mainly in the front: torque converter and pump; overdrive, underdrive, and reverse clutches; and valve body), and some derived or taken from the 68 (low/reverse clutches, planetary gearsets, and 2C clutch).
The reaction sun gear is welded to the 4C/reverse hub on the heavier-duty transmissions; in addition, the input and reverse planetary assembly includes the reaction annulus, welded to the reverse carrier. They do not use a #7 thrust bearing; the #11 bearing is in the input and reverse planetary assembly. Otherwise, the planetary gearset thrust bearings are the same on all RFE transmissions.
Service notes: 66RFE and 68RFE automatic transmissions
The transmission-control computer is in a single module with the powertrain computer. During limp mode, the manual valve provides reverse, neutral, and fourth gear.
Two filters are used, a spin-on type on the cooler return, and a sump filter on the valve body; both use the filter previously reserved for 4x4s. Like all Chrysler-engineered automatics, they use ATF+4 transmission fluid.
The underdrive, overdrive, and reverse clutch assembly snap rings are not interchangeable between transmissions. The tapered side of the two tapered snap rings in the input clutch must face up.
Underdrive clutch clearance is not adjustable, but reverse clutch clearance is, via a selectable snap ring. Overdrive clutch clearance is adjustable on the 68RFE (using a selectable overdrive/reverse pressure plate), but not on the others. 4C clutch clearance is adjustable via a selectable snap ring.
The 2C clutch on the 66 and 68RFE has one more disc than the 545RFE, and the 66 and 68RFE piston is shorter. The 2C reaction plate has to go in first when rebuilding the 2C clutch, not the separator plate.
The 68RFE automatic transmission is made in Indiana Transmission Plant I, which also made the 545RFE automatic.