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Jmyers

48RE in 2007 Ram Truck Shifts by Itself

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I have an 07 Dodge dually with 5.9L and automatic tranny. It seems worse when it's hot outside and may not even do it at all in cooler months, but when running highway speeds, 70+ MPH, in the warmer months it will kick in and out of OD and sometimes the tranny temp light comes on and dings. When it does this the Tow/Haul and OD Off indicator in cluster changes. Of course it's cooler now, but getting ready to tote toy hauler to Arkansas from Texas and take it to tranny shop and they see no codes and it's shifting fine. Thoughts?

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Jmyers...Welcome to the forums...First off, you have an earlier 2007 with the 5.9L Cummins engine and 48RE four-speed automatic.  Sounds like you might have an issue with either the Tow/Haul switch mechanism at the lever or within the circuit for the Tow/Haul mechanism.  Also, on my '05 3500 with the 48RE, the Tow/Haul function can be reprogrammed (a software reflash) to serve as an overdrive lockout.  In this case, the Tow/Haul function and button circuit is converted to a switch for opting in and out of the OD mode.

 

As an aside, I have considered re-flashing my Tow/Haul to be an OD lockout.  The Tow/Haul mode, other than boosting the shift apply pressures, is not to my liking other than its grade hold function, which can be accomplished with braking then manual downshifting and hold.  (I do like Tow/Haul for providing downgrade support, including intuitive downshifting and holding in the lower gears with a load in tow.)  The knocking back and forth between overdrive and 3rd gear, however, is always brutal on any four-speed overdrive automatic, whether Chrysler, Ford, GM, Aisin or ZF.  I would prefer being able to simply switch out the overdrive mode and hold 3rd gear when desired, like on long upgrades or even downgrade compression braking.  Instead, I'm altering my speed to protect the transmission from knocking between OD and 3rd gear. 

 

Does your setup have a function for both OD lockout and Tow/Haul mode?  Please clarify the normal function for your transmission with regard to OD and Tow/Haul modes.  I can provide insight into deeper problems in the system or within the transmission itself, but that might be premature if the issue is an intermittent short in the OD or Tow/Haul button mechanism or that wiring circuit.

 

The transmission temperature, unless you have an aftermarket gauge on the transmission pan, requires troubleshooting.  If the transmission is actually hot enough to trigger the alarm, that's a problem.  So if that sensor system is accurate, and you have an actual overheating problem, I would suspect transmission cooler clogging.  How many miles do you have on the truck?  These coolers are prone to clogging at higher mileage if debris like clutch friction or band material and thrust wear from within the transmission finds its way to the cooler.  Another issue is a defective thermal valve at the cooler when stuck in the cold operation bypass mode.  Fluid circulates around the cooler instead of through its core.

 

I would perform some tests...With the truck warmed after a good run, preferably under load, take an infrared thermometer and probe the input side of the transmission cooler and supply line from the transmission.  (The cooler is in front of the radiator on the 5.9L Cummins applications.)   This can be done with the engine idling and in Park with the parking brake set.  Probe from under the hood, don't get under the truck.  Then probe the return line in the same way. 

 

There should be a distinct drop in temperature between these points across the cooler.  Also check the core of the cooler at different areas.  See if there are any hot or cool spots.  You can probe the transmission case and the transmission oil pan temperatures with the engine shut off after a loaded run.  The infrared thermometer can be held some distance from the heat sources to protect yourself.  Chock wheels if sensible, set the parking brake, make sure the transmission is in Park, the usual precautions before crawling under the truck.  Avoid hot areas and risk of burns.

 

A thermal sensor/gun is a valuable troubleshooting tool.  It doesn't have to be an expensive one.  I use mine for many automotive troubleshooting chores. 

 

Moses

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The switch on the stalk does allow you to select between normal O/D operation, Tow/Haul Mode and O/D Off. I do like to operate under load using the Tow/Haul mode for lockup and shifting characteristics. I have wondered about the switch or wiring since it is so intermittent. The temp light flashes on and off so quickly that you can rarely hear the ding and look down in time to still catch it on.

One thing that I read on another forum is that there is a check valve near the radiator that can malfunction and clog not allowing proper flow and also allows fluid to drain back and out of the converter. I can say that if I haven't driven it in two or three days it does take some time to get her rolling after putting it in gear like it has drained back.

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Jmyers...Sounds like the OD and Tow/Haul switch mechanism or circuit is faulting.  The temp light flash could be as simple as a poor connection issue or intermittent open/short, although I still suggest checking the actual transmission and cooling line heat with a simple thermal gun test.  That way you can eliminate concerns about a real overheat.  In particular, make sure the transmission cooler is dropping the temperature properly.

 

The check valve you describe is the cooler line anti-drain back protection for the torque converter, a subject that I've discussed at these forums and also cover in-depth at the magazine.  Review this article and the Sonnax solution:  http://www.4wdmechanix.com/Survival-Upgrades-for-Jeep-and-Dodge-Ram-Automatic-Transmissions.html.  You do have the drain back problem that I discuss.  Startup with no immediate gear engagement means the fluid has drained back and left a very low fluid level within the torque converter.  As you'll discover in the article, there are also more valve body issues that can develop, in particular the manual (shift) valve sticking in Park.

 

When you have that delay before gear engagement, the front pump bushing in the transmission is susceptible to running dry, causing premature front pump bushing failure.  This is a Chrysler RWD transmission issue that dates back to the 904 and 727 three-speed automatics, predecessors to the later electronically controlled, four-speed automatics, including the most advanced, strongest and last of these transmissions, our 48RE.

 

Moses

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