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The 68RFE and 66RFE automatic transmissions for Ram trucks

Chrysler’s new 45RFE transmission, launched in 1998, used three planetary gear sets instead of the normal two. The transmission evolved into the 545RFE, and then the 68RFE (2007), and the 66RFE (2012), a lighter-duty version of the 68RFE; the main differences between the various 6*RFEs are reportedly in the torque converter.

545RFE

The 545RFE had five normal forward gears and a sixth used for kickdowns only. The 68RFE kept the basic clutch and hydraulic control design, matched with heavier-duty planetary gears, toothed differently to increase their capacity. The shafts, clutches, pump, torque converter, and other parts were also redesigned to handle the Cummins 6.7 liter diesel.

The 263-pound 68RFE has roughly the same torque capacity as the Aisin automatic option in Ram heavy duty pickups, but the Aisin allows for a power takeoff (PTO) and the 68RFE does not; the Aisin also had 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).

Gear ratios123*456R
545RFE / 65RFE3.001.671.501.000.750.673.00 or 2.21
Aisin AS68RC3.741.961.341.000.770.633.54
66RFE / 68RFE3.231.841.411.000.8160.6254.445
* “Prime” gear used for kickdown only

A “Tow/Haul” mode allowed faster, crisper shifts, to reduce wear.  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 highway efficiency. Electronic Range Select let drivers limit the highest gear, using a +/- switch on the column shifter in the Ram Heavy Duty. Allpar’s test drive commended the transmission (in 2010) for rapid kickdowns and general responsiveness.

68RFE automatic transmissionThe torque converter locked up in every forward gear except first, based on temperature, gear, tow/haul mode, and exhaust brake activation. It used a computer that did not allow retrofits into earlier trucks.

Owners pointed to weak spots in the 2007-11 units, 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 2012 66RFE and 68RFE had a wider overall gear range than the 545RFE/65RFE; they can be identified with a label on the transmission case that shows the part number and build sequence (also stamped into the case, below the label).

Service notes: 66RFE and 68RFE automatic transmissions

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 transmissions, as used in 2012 and onwards, have a single-piece case, two-stage 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 66RFE 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).

68RFE

The reaction sun gear is welded to the 4C/reverse hub on the heavier-duty transmissions; and 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.

The transmission-control is built into the powertrain computer. During limp mode, the manual valve provides reverse, neutral, and fourth gear.

There are two filters, a spin-on type on the cooler return, and a sump filter on the valve body; both use the filter previously reserved for 4x4s and 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.


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