Home How-to Articles Ram Truck 47RE and 48RE Transmission In-Chassis Survival Upgrades from BD Diesel Performance

Ram Truck 47RE and 48RE Transmission In-Chassis Survival Upgrades from BD Diesel Performance

by Moses Ludel

Chrysler’s Ram truck 47RE and 48RE transmissions have a checkered history.  Derived from the rugged 3-speed A727 Torqueflite with an add-on 4th gear/overdrive sandwiched into the unit, these stock RE transmissions have an unpredictable lifespan. The magazine’s 2005 Ram 3500 4WD with 5.9L Cummins diesel power, purchased new 13 years ago, has now clocked 162-thousand miles on its 48RE without a rebuild in sight—possibly some kind of record.  To put this into perspective, however, our transmission has been upgraded with select Sonnax components covered in detail at the magazine.

For rebuilders of OEM transmission units, Sonnax offers a variety of components that improve the function and reliability of 47RE/48RE transmissions.  To review the Sonnax survival upgrades in our 48RE transmission, go to https://www.4wdmechanix.com/Survival-Upgrades-for-Jeep-and-Dodge-Ram-Automatic-Transmissions?r=1.  Sonnax serves the independent transmission rebuilding industry.

The A727 architecture that spawned the RE overdrive transmissions was actually quite stout.  A727 Torqueflites, launched by Chrysler in 1962, survived in hemi-power muscle cars and Class A motorhomes.  If there is a Achilles’ heel in the RE transmissions, it would be the overdrive ratio (31% or 0.69) that produces considerably higher loads than the earlier 3-speed versions of the A727 or even the lighter duty A904/999 or Jeep 30RH/32RH.  These legendary 3-speed units were popular in Dodge trucks (under the moniker “Loadflite”), I-H light trucks and Scout II models, many Jeep vehicles and importantly the rugged Jeep FSJs including the Grand Wagoneer.

Since automatic transmission overdrive units handle the highest loads and punishment, it is imperative that drivers should have the ability to lock out the overdrive under severe or taxing driving conditions.   The 2005 Dodge Ram trucks have the singular distinction of no overdrive lockout provision.  Chrysler believed that TCM’s software programming and the programmed “Tow/Haul” mode could eliminate the need for a driver shift control.  Notably, RE transmissions prior to 2005 and after that model year do have an overdrive On/Off button, which should used whenever the transmission is subjected to excessive loads.


The BD Diesel Performance OverDrive Lock-Out module is strictly for 2005 Dodge Ram trucks with the 48RE transmission.  This is the only model year of the 48RE that does not have a provision for manually locking out 4th gear/overdrive.  Chrysler incorporated a Tow/Haul mode that serves some vital functions but does not allow over-riding.  When the factory programming dictates, the 2005 48RE transmission shifts into overdrive.  Often, the stock 2005 48RE transmission stays in overdrive despite a severe load.  On long grades, the programming may hold the transmission in 4th gear/overdrive, creating severe engine and transmission stress with excessive heat.

In our latest HD video how-to coverage, we install the BD Diesel Performance Electronics Upgrade Kit and the BD OverDrive Lock-Out module for the 2005 Ram 48RE transmissions.  The aim once more is to keep our transmission off the work bench!  On steep grades with a trailer, the stock 2005 model 48RE is especially vulnerable to damage as the transmission shuttles between 3rd/direct and 4th gear/overdrive.  BD Diesel Performance’s overdrive lockout module can interrupt the upshift to 4th gear, holding the transmission in 1st, 2nd and 3rd (direct) gears.  This device does not in any way interfere with the other factory shift functions.

Overall, the stock 47RE/48RE’s 31% overdrive is too much gear spacing.  The ability to hold the transmission in 3rd gear, while at the same time dropping vehicle speed to a reasonable engine rpm level, takes a tremendous load off the 48RE’s overdrive components.  (For details on the overdrive design and weaknesses, see our forum discussion at http://forums.4wdmechanix.com/topic/971-2006-dodge-ram-48re-overdrive-not-working/?tab=comments#comment-6510.) Our Ram truck’s gearing (4.56) and tire diameter (36.5″) translates as 52-55 mph at 2100-2300 rpm in 3rd gear.  With our typical trailer weight of 8,400 pounds on a 6% or steeper grade, this is plenty fast if you want to preserve your Ram’s powertrain!

BD Diesel Performance strongly focuses on the popular diesel powered light trucks.  This includes Ford Powerstroke, G.M. Duramax and Dodge Ram/Cummins needs.  Shown are the BD Diesel components for keeping a Dodge Ram’s 47RE or 48RE transmission going.  These upgrades are “in-chassis” projects that can be implemented on any transmission in good operating condition.  The BD heavy duty aluminum oil pan is rigid enough to reinforce the RE transmission’s case and adds 2 extra quarts of fluid plus cooling fins to drop transmission temperatures and extend the fluid’s service life.


Dropping the transmission pan at 162,000 miles yielded this pleasant surprise once more:  no metallic pieces, thrust material or signs of abuse, just normal wear indicating that our 48RE is still intact.  We’ve been pulling a Holiday Rambler travel trailer to events, and being able to lock out overdrive under heavy loads, on steeper grades or when bucking congested freeway traffic is just what our transmission needs.  The transmission’s dipstick remains spotlessly clean and free of any heat signs, a hallmark of our protecting this transmission since new.  While driving method is largely responsible for our 48RE’s success story to date, the fluid choice has always been Mopar ATF+4.  Be sure to run a recommended synthetic automatic transmission fluid in these RE transmissions!

Changing the failure prone OEM governor solenoid and transducer is good insurance with several performance benefits.  Our goal is transmission survival.  These upgrades will help keep the transmission functioning properly and not leave us stranded alongside the road with a defective governor solenoid, transducer or wiring.  At right, the factory plugs that will be reused require extreme care when separating and attaching them.  The red interlock latches, in particular, need close attention.  Do not force these pieces apart, there is a specific sequence to unlatching the tabs before sliding connectors loose!

The governor solenoid retention bracket also secures the OEM transducer.  This bracket must be modified or replaced with an earlier design bracket.  To be sure that the new governor solenoid seats firmly in the governor plate, the bracket’s U-shaped shoulder was carefully bent downward, enough to press the solenoid against the governor plate’s machined seat.  If the transducer tab is cut off (see video details), polish rough edges and remove all debris before assembly…When the bracket is installed with the governor ledges bent downward properly, the ledges will engage the slot in the governor solenoid and push the solenoid’s flange downward against the governor plate’s seat.  Use care to protect the O-rings during installation.  Once installed properly, the upgrade Borg-Warner governor pressure solenoid should perform flawlessly…Ours did.


Band adjustment is a periodic interval service on the RH/RE transmissions.  These are the last of the Chrysler band-type transmission units that require adjustment.  When the 47RE or 48RE is well-maintained, this service can take place every 30,000 miles or so.  Our 48RE’s bands have only been adjusted three times in 162,000 miles.  The need for more frequent or significant adjustment is cause for concern:  Band and clutch friction material is stout but relatively thin by design; “wet” clutches and bands should only wear a slight amount.  (Most often, the need for adjustment is due to drum wear or the metal stretch and wear at band backings or metal contact points.)  Though important to adjust the bands, there should be only a small degree of take-up adjustment required over the useful service life of these transmissions.  The how-to video covers the fundamental band adjustment steps for a 48RE.  At right is the ATF recommended by Mopar® for the 48RE transmissions.  Failure to use the correct fluid can result in overheating and dangerous clutch or band slippage, either of which leads rapidly to transmission failure.


The BD Diesel Performance ‘OverDrive Lock-Out’ kit for the 2005 Dodge Ram 48RE transmission is a welcome offering!  We are very pleased to note that BD Diesel Performance has faithfully provided this module and installation kit for many years.  Despite being a one-year model issue, BD Diesel Performance continues to make the kit available—and we’re grateful.  The lockout allows driving a 2005 model year truck with far more control than Chrysler allowed.  The transmission can be held in 1st gear, 1st-2nd gear or 1st-2nd-3rd gears—without taxing the transmission under severe load conditions.  When overdrive is desired and practical, simply unlock the module, and the transmission seamlessly shifts to overdrive under its factory programming schedule.

Our 2005 Ram 3500 4×4 can be driven just as it always has been—or we can manually control the shifting.  The 48RE will survive much longer with this level of control, especially while towing and under load.  Keep in mind that there is no set lifespan for any automatic transmission.  A stock 47RE (A518) or 48RE (A618) automatic transmission can fail in mere miles while towing on a steep grade under severe load.  If you want your 47RE or 48RE automatic transmission to survive like our 48RE has to this point, drive sensibly and protect the transmission with the BD Diesel Performance 47RE/48RE Electronics Upgrade Kit and Sonnax upgrades.  If you own a 2005 Ram with the V-10 gasoline engine or a Cummins 5.9L Cummins diesel power and the 48RE, the BD Diesel Performance 48RE OverDrive Lock-Out module kit is a must.

If you have powertrain needs beyond these remedies or want the ultimate replacement transmission, engine upgrades or performance parts, see the BD Diesel Performance website and a catalog full of powertrain upgrades:


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John Skinner August 13, 2020 - 6:08 pm

Love your website. Was interested in the longevity of my 48RE trans in my 03 Ram 3500 4X4 diesel. You said yours went 162,000 so far. That’s a good deal. I pull a 24′ RV trailer and have racked up 185,000 miles so far with no trans problems. I change the filter and oil every 30,000 religiously. Is lasting better than I ever imagined. One band adjustment..

Moses Ludel August 13, 2020 - 9:22 pm

Thanks, John…The 48RE is not a bad transmission…Ours is mostly stock and has delivered over 180K miles now. We bought the truck new and have pulled a car hauler and RV trailer about 12%-15% of the total mileage. I did do the valve body upgrades from Sonnax. (See the Sonnax upgrade coverage.) More recently I have been running the BD overdrive lock-out, which enables eliminating third-to-fourth/overdrive shifts when scaling grades or towing in heavy traffic. My 4.56 axle gearing with 37″ diameter tires is just a bit lower than stock tires and the original 3.73s, more like 4.10s with the original tires. I change the pan fluid and filter with a band check every 40K or so miles.

These factors have contributed to the 48RE’s survival. By design, this transmission is the best factory build of the RH/RE series transmissions, and it does have improved planetary units. Compared to the later 68RFE, many now argue that the 48RE is better for racing applications and easier/less costly to rebuild when necessary. It’s a fundamental automatic transmission derived from the rugged A727 three speed. The additional planetary system for overdrive is the weak link. The best automatic transmission survivors to date are the later Ram/Aisin units and G.M.’s Allison.

Of course, the amount of torque available from an H.O. or modified Cummins engine can quickly destroy any automatic transmission. In my view, our transmissions last because we drive sensibly. I avoid the kind of slippage caused by heavy throttle at gear changes and never overheat the 48RE by pushing it hard with a trailer in tow. Overdrive is for light cruise, the truck unloaded on the interstate and flat ground towing without a heavy headwind. Lightening the throttle load at shift points will also extend the life of these transmissions. I’m not one for running hard through the gears or over-revving a diesel engine. Typical highway engine speed is 1800-2200 rpm, even slower when striving for maximum fuel efficiency.

I’ve considered an Allison conversion, even a manual transmission like a medium duty 7-speed truck unit with overdrive. I keep expecting the 48RE to need a routine rebuild, which I will do myself. There are moderate upgrades that make sense. To date, however, the transmission has shown no signs of giving up…If this transmission goes 240K miles without a bench tear down, I will be more than pleased. If a 48RE can go that many miles in relatively stock form, I would expect 350K miles from a painstaking rebuild with upgrades. That’s a good life for any automatic transmission.

There are many automatics that have failed in just one trip from heavy throttle towing and knocking in and out of overdrive under summer heat. I slow down, lock out overdrive and save the transmission. I’m sure you’re using good judgment when towing the 24′ RV trailer. Driving technique has a direct impact on automatic transmission life.

Enjoy your Ram truck!



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