top of page
  • Writer's pictureCAC


The older automatic transmission dating from 1989 to 2002 when the 47 RH then the 48-RE transmissions were introduced were designed after the 727 Torqueflight Chrysler transmission and were never suited for the diesel market. The 47- RH and the 48-RE continued to use very old technology that has been passed on for many years. Utilizing bands, hydraulic throttle valves and governor pressure to control shift timing, the 48-RE transmission will never be a smooth shifting transmission or have the consistency of the newer designed transmissions. The first three gears of the 48-RE are spaced evenly while the 4th gear is a massive jump into overdrive. The big jump into overdrive creates a large RPM drop into 4th gear making it somewhat unpleasant for towing. The lock-up torque converter was added as an afterthought to the already outdated low-line pressure transmission making it difficult to control the application of the converter clutch providing unpleasant TCC shifts. If you’re looking to tow a trailer or go for more horsepower, the 48-RE transmission is not the best transmission choice. Although the 48-RE can be upgraded, it will always be limited by bands, case issues and only 4 gears! Once upgraded the general consensus on the street is each re-built 48-RE lasts for less miles than the one before! (The majority of our customers have gone through several)

The 68-RFE transmission has a much better gear split between its 1st through 6th gears providing gear ratio change that is in fact very close to the Allison 1000 transmission. The torque converter is a PWM design allowing for precise application of the converter clutch which provides a smooth shift. Unfortunately, this is where all praise for the 68-RFE ends. The 68RFE's wait until 4th gear to lock the converter and when they do, they partially lock - or modulate - into lockup. The 68-RFE transmission was clearly designed to be the least expensive to manufacture. As a result, there are many elements that must be upgraded in this transmission to make it reliable and handle higher power levels. Even the transmission case is cheaply designed and must be reinforced with a large aluminum pan and transmission brace over the top to keep if from cracking in half. The 68-RFE internals are actually larger versions of those found in a Dodge Caravan transmission that originally debuted in 1989. Chrysler used this basic design and adapted it to be used behind their gas engines calling it the 545-RFE. They then made a few parts in the 545-RFE transmission a little larger again to then be used behind the Cummins which eventually became the 68-RFE that we know today. The 68-RFE can be rebuilt with upgraded parts making it a great shifting transmission but it is limited because of the small clutch packs, gear sets, poor valve body design and shafts that make up the transmission. Similar to the 48-RE, the money spent in strengthening the internals of the 68-RFE is likely better suited to be invested in the Allison conversion. If you were to spend the money to upgrade the internals of the 68-RFE, you would still be left with a transmission that has clutch packs, gear sets and shafts that are nearly half the size of those in the Allison. For those that currently have an Aisin 68-RC, AS-69RC or AS-66 RC, upgrading to the Allison is the only logical choice. The Aisin transmission suffers from many of the same shortcomings as the 48 –RFE & the 68-RFE but also has its own unique issues. Currently there are limited hard part upgrades for the Aisin’s and there are many areas that need to be addressed, not only for strength but for longevity. Factory replacement parts are 2 to 3 times the cost of conventional parts which drives the cost of rebuilding the Aisin to a level that is unreasonable for most, not to mention the difficulty in getting factory parts at all, as they come from overseas they are often back ordered, leaving your truck disabled for unreasonable periods of time. For these reasons, Custom Automatic Conversions, (CA Conversions, CAC) has focused our efforts on making the Allison 5 or 6 Speed Conversion affordable for anyone that needs to replace a Dodge transmission. An additional benefit of the Allison is it learns your driving style, through real adaptive learn! Different drivers, power levels, habits, etc. The Allison TCM will adapt to them all providing optimal shift transitions through all gears. Tap shifting capabilities remain the same for all 6.7L Cummins with the 68 RFE or an Aisin, but CA Conversions has perfected tap shift for any vehicle you put a 6 speed Allison in, 12 valve, 24 valve or 5.9L Cummins! For the 6.7L Cummins you can use the factory shifter and for older trucks you can purchase a new shifter, which can be installed in a matter of minutes, yet retains all factory functionality or we produce a rocker switch which can be installed in minutes for the purpose of manual shifting. Overall, the Allison can handle more power, with more functionality and longevity than other transmissions. An Allison Swap is a solid choice whether you want it for your daily driver, tow a lot or want to take your truck down the sled pulling track. The best all-around transmission for a person that tows, wants to use the power of their high horsepower Diesel, is looking for reliability above all and still would like to have the ideal shifting transmission is The Allison 1000! CAC makes it possible to mate one to the Cummins engine! This means you can take any Allison 1000 transmission and put it behind the Cummins. As great as the Allison transmission is, in certain cases the stock Allison transmission does have limitations, the great news is, thanks to CA Conversions years of installing the Allison transmission in dozens of different applications, we have learned that the Allison can affordably be upgraded to handle levels of abuse and horsepower while also providing reliability and longevity!

In order to properly install the Allison transmission into the Dodge Pickup there are many areas that CA Conversions has addressed. We've tackled how the transmission is adapted to the engine using our billet adapters and specially designed flex plate, retain all the functionality and features of your 4 wheel drive with our patent pending transfer case adapter, cooler line adaptation, shift linkage and cross member mounting kits, dip sticks and multiple TCM configurations providing proper implementation of the throttle voltage of your truck. The only modification required in the drive train is shorting and or lengthening of your drive shafts! Your engine calibration has to be modified to a manual mode calculation, so the engine will no longer look for the Dodge transmission, then the CA C complete harness system PROPERLY runs the transmission in a stand-alone mode utilizing throttle voltage. If this is not done, once the factory automatic transmission is removed, and the ECM is not re flashed, the ECM sees this as a fault and the engine defuels and limits power so as not to cause any damage. There are many companies that provide custom tuning to recalibrate the engine computer module, while doing the Allison Conversion, this step will have to be done in order for the engine to run properly. We can recommend the right tune for your application, as well as the tuning company to utilize, so you can to get the optimal tune for your application. Give us a call at 865-253-1133, 7 days a week, to find out about this exciting option for your truck.

Contents of the Allison Conversion Package:

  • Adapter & Flex plate

  • Transfer case adapter (4WD)

  • Properly programmed TCM and CA Conversions proprietary, blue (5 speed) or black box (6 speed)

  • Mounting kit

Options, you can purchase from CAC:

  • Re-manufactured Allison 5 or 6 Speed transmission (all new electronics)

  • Several custom torque converters designed to work PROPERLY to enhance your conversion.

  • Gear reduction 6.0L Ford style starter

Recent Posts

See All
bottom of page