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Sorry If this topic has been addressed elsewhere but I have been unable to locate anything relevant. 

Here goes.

I have a 2006 Dodge truck with 5.9L diesel and 48re auto trans. All stock no chips- no previous mods -very little towing (one hand times to haul cattle). At 93000+ I got the dreaded cracked overdrive housing ( discovered in short order due to fluid loss). Replaced the overdrive with a rebuilt one from a reputable parts vendor and during this operation did the suggested 48re survival update (sonnax parts) recommended on this site. Yes I was lurking and learning. Also adjusted band to factory specs. Trans show marked improvement in the shifting department but the overdrive does not appear to be working, so my engine rpms are in the upper range. Could any one offer any suggestion on where to begin addressing this issue.

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Hi, w1ldw1ll...Glad you did the Sonnax upgrades and were happy with the results.  Your 1-2, 2-3 upshifts and downshifts seem normal, and you believe you're not getting a 4th gear.  With the 4th gear ratio of 0.69:1 or 31% overdrive, this makes a noticeable difference in rpm!  You trust the vendor source for the rebuilt overdrive, but let's consider any and all possibilities for a no-shift to overdrive.  The lock-out button would be the first place to look if recent work was not performed, so we'll include it but also the other possibilities.  These are the FSM factory troubleshooting steps and the recommended solutions for this symptom.  In red are my comments related to your description of the problem and the work you have performed:


1. O/D Switch In OFF Position: Turn control switch to ON position.   Obvious fix here...

2. Overdrive Circuit Fuse Blown: Replace fuse. Determine why fuse failed and repair as necessary (i.e., shorts or grounds in circuit).  Check the O.D. circuit fuse...You've been working around the O.D., maybe a lead went to ground, shorted and blew a fuse.  Could be this simple and easy to fix.

3. O/D Switch Wire Shorted/Open Cut: Check wires/connections with 12V test lamp and voltmeter. Repair damaged or loose wire/connection as necessary.  Worth considering, the only trouble is in overdrive, could be a loose or shorted lead.

4. Distance or Coolant Sensor Malfunction: Check with DRBT scan tool and repair or replace as necessary.  Not part of your work or the original problem, this is a weak prospect.

5. TPS Malfunction:  Check with DRBT scan tool and replace if necessary.  Again, not part of your work or initial problem, another weak prospect...

6. Neutral Sense to PCM Wire Shorted/Cut: Test switch/sensor as described in service section and replace if necessary. (Engine no start.)  Worth checking though this is low on my list.  You're not experiencing a no start.

7. PCM Malfunction: Check with DRBT scan tool and replace if necessary.  Weak prospect here, this would be a whole new issue...Low on the list.

8. Overdrive Solenoid Shorted/Open:  Replace solenoid if shorted or open and repair loose or damaged wires (DRBT scan tool).  If you were near or around the solenoid during your work, this is worth testing...Somewhere on the list if other tests do not find the problem.

9. Solenoid Feed Orifice in Valve Body Blocked: Remove, disassemble, and clean valve body thoroughly. Check feed orifice.  Possibility, this is valve body and solenoid/O.D. related.  Would be an odd coincidence if you simply installed the Sonnax parts, and the O.D. feed orifice became blocked.  This might be related to your overdrive unit replacement but would be lower on the list.

10. Overdrive Clutch Failed: Disassemble overdrive and repair as needed.  This could be related to the rebuilt overdrive unit.  Your call on whether you want to condemn the O.D. unit.  Eliminate the other, easier possibilities first before isolating the O.D. clutch as a candidate.

11. Hydraulic Pressure Low:  Pressure test transmission to determine cause.  Unless you reset the pressure regulator spring adjustment during the Sonnax parts installation at the valve body, this prospect would be unlikely.  You are not experiencing issues with up- and down-shifts in those three forward gears and reverse that operate.  Pressure can be checked at the 48RE's pressure test ports if necessary.  This is well down the list judging by the general performance but certainly a test that is vital when there are shift or slippage issues beyond what you're experiencing.

12. Valve Body Valve Stuck:  Repair stuck 3-4 shift valve, 3-4 timing valve.  This is a possibility whenever a valve body has been apart and put back together.  Misaligned plates, balls out of place, springs in the wrong position, debris introduced to a precision fit bore(s), even lint between valves and bores, the possibilities abound.  Of course it's work to remove and strip down the valve body again...Try all of the easier prospects first!  

13. O/D Piston Incorrect Spacer:  Remove unit, check end play and install correct spacer.  This is an important question.  Since you installed a rebuilt O.D. unit, you likely did not check this end play to confirm whether it's correct.  As part of the rebuilt unit, this item should definitely be on the check list.  Again, check the easier stuff first. Removing the O.D. is not a light task...Is your truck a 4x4?  If so, there's even more work accessing the O.D. unit.

14. Overdrive Piston Seal Failure: Replace both seals.  Again, part of the O.D. rebuilt unit.  This is a real possibility if the lighter prospects do not turn up a problem/solution.

15. O/D Check Valve/Orifice Failed: Check for free movement and secure assembly (in piston retainer). Check ball bleed orifice.  Once more, related to the rebuilt O.D. unit.  This should be on the list.  It's much easier to reflect on work we perform ourselves, harder to qualify and speculate whether others have created an issue...

I trust this is helpful.  Certainly a place to start.  Let us know what you find, it would be great if the problem is simple to fix...



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You're very welcome...Others will benefit, too.  

The 48RE gets a bad rap, our unit with the Sonnax upgrades has 154K miles on it with no signs of giving up.  I've towed trailers maybe 12% of that mileage, and I'm diligent about not forcing downshifts, allow upshifts without lag or "slip", try to avoid shifting under detent/kickdown and generally "baby" this unit.  I may be working on a record for reliability on an OE unit with only the modifications you've seen, it's really about the way we drive an automatic transmission.  

The worst strain on these 48RE units or any automatic O.D. transmission like it is the shifting in and out of overdrive under load.  I recommend switching or locking out O.D. on long upgrades; slow down to accommodate 3rd gear rather than allow shifts back and forth between 3rd and O.D.  Our '05 does not have the O.D. lockout, instead the button is for "Tow/Haul" mode, and I will likely get the B.D. elimination kit to get rid of this one-year, useless anomaly.  Your '06, fortunately, can lock out the O.D. with the shift lever button.

I'm sure that when you had the pan and valve body removed you were astounded by the apparent frailty of the 48RE OE components, especially the bands, struts and band apply pistons.  That would seem like enough to make us baby these units, yet the original A727 3-speed automatic, from which this unit was derived, had been fitted behind 426 Hemis in the muscle car era and pulled motorhomes up 8% grades behind 440 Mopar wedge-head V-8 engines.  I keep this in mind and expect this transmission to deliver decent service.  Debris in the pan during the oil changes has been normal and minimal, I have used Mopar ATF-4 (synthetic) fluid.

Question:  Did you eliminate the anti-drainback valve when modifying the valve body with the Sonnax upgrades?  Do you have the stock trans cooler or an aftermarket unit?

One appealing thought if you intend to keep your 2006 Ram "forever" would be the Allison transmission conversion.  I saw this at the recent SEMA Show in the CAConversions booth, they have a website with some reassuring testimonials:  http://www.caconversions.com/.  I'm keenly interested in the approach.  Many do high performance builds of the 48RE, and I'm fully capable of doing that myself, but that route is expensive and still uses the same cases that you saw go south.  The 6-speed Allison takes the powertrain to new heights and is actually a match for the Cummins torque and heavy loads.  UPS vans with the 12-valve Cummins 5.9L ran these units.

Note:  I'm running 4.56:1 axle gears and with 36.5" diameter tires, so my 70 mph engine speed is 2056 rpm in O.D.  The 6th gear of the Allison 1000 unit is .61 ratio, which would drop my rpm to 1817, optimal for improved mileage and torque advantage!  A double gain: reliability and 6 speeds that offer a suitable gear for every speed and load.

Please let us know how your troubleshooting unfolds.  I'm crossing fingers that an easier fix will work, but if necessary, you have the full list of possibilities at your disposal!


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Not sure what you meant by anti drain back mod. I followed the "48re survival guide" and was meticulous about keeping all valve body parts clean during reassembly. One nagging thought is the shim for the overdrive, as I did not have shims , I installed the existing one. Could you expound on what the purpose of that shim is and how it might affect the od operation?

I certainly appreciate your advise as I am certainly not a tranmission technofile, as per your above communication, I only want to keep the truck running as it is the devil I know (or am coming to know).


Thanks again.

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w1ldw1ll...Regarding the shims/spacer, I've generated a PDF from FSM coverage.  Here are the steps for setting the O.D. spacer clearance at the intermediate shaft.  The concern here is proper endplay of the intermediate shaft, which should not change if you installed the OE spacer and the replacement overdrive unit was rebuilt to proper specifications.  Judge for yourself, and if you have further questions about the spacer or your overdrive unit rebuild, we can go further:

48RE Overdrive Spacer and Intermediate Shaft Endplay.pdf

The anti-drainback valve is in a transmission cooler line.  The valve closes when the engine shuts down and transmission fluid pressure ceases.  An anti-drainback valve prevents the torque converter fluid from draining back to the transmission when the truck is parked.  This valve, if defective, stuck open or otherwise not preventing drainback, will allow the torque converter to drain.  

This is a damaging situation for the front pump bearing.  Chrysler designed all of the RWD 904/727 derivative transmissions, including RE/RH OD types, to not fill the torque converter when the engine is running in Park mode!  This means you start the truck up, let it idle for a time in Park, and if the anti-drainback valve is defective and allowing fluid to drain from the converter, the front pump bushing is running dry the whole time...I discussed this in the Sonnax article at the magazine (see http://www.4wdmechanix.com/Survival-Upgrades-for-Jeep-and-Dodge-Ram-Automatic-Transmissions?r=1) as the reason for using the constant pressure/lube valve to charge the converter whenever the engine is running and regardless of the selected shifter position.

So when you installed the Sonnax orificed pressure lube valve (assuming you did), Sonnax instructions called for eliminating the anti-drainback valve.  On our models, unlike earlier Chrysler RWD cooler hoses or pipes with an anti-drainback valve that's simple to access or replace, our anti-drainback valve is built into the line.  We can discuss this further if you're interested, but it sounds like you overlooked this step, and in my case, I avoided it.  I am curious because I have high back pressure at the cooler when the thermostatic coupler closes and directs fluid through the cooler.  

This back pressure may have affected the downshift characteristics.  The only symptom is a harsh downshift when coming to a complete stop. I'm curious whether the Sonnax modifications affected your transmission's downshift to second and first gear as you come to a complete stop, and if so whether that's all the time or only when the transmission warms.

The anti-drainback valve likely has no relationship to overdrive, which in my 48RE works fine.  All of my shifts up and down are very smooth and precise until the truck is nearing a complete stop at normal slowdown speed—then the shift to first gear is harsh.  The only way to compensate and soften this downshift to 2nd/1st gear is to stop gradually or come to an abrupt, hard stop.  

I plan to remove or modify (whichever works best) the anti-drainback valve shortly to see if this cures the issue and also flush the transmission cooler.  If that's not the cure, I will troubleshoot the cause further (governor solenoid and some other possibilities) and eliminate the harsh downshifts when the transmission is warmed and the truck is coming to a stop.  The thermostatic coupler redirects fluid through the cooler (bypass mode ends) at approximately 50-degrees F in the transmission...Your experience?  




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I'm sure you've guessed by now I am not well versed in automatic transmission technology (and this has been a learning experience- Its broke so let's fix it) 

I did read the service manual prior to disassembly and replacement of the overdrive unit. That was the reason for purchasing a rebuilt unit -I lacked the proper tools to safely and correctly repair the unit. During assembly I paused at the shim installation, but having no other shims I danced with the one what brung me. Everthing bolted tight so lets see what happens? (yeah I know dats a lotta work if it don't - still have fingers crossed that Murphy is hiding else where and I intend to run him down).

Yes, I missed the drain down mod although I do remember the issue and reason for it. AS to rough down shifting haven't experienced it yet but, have been trying to go easy on this trans until all is working.

My heart and mind say "aye" to the Allison conversion, but the better half and my wallet say otherwise. To be honest I haven't read the article you referenced (life happens) but I will.

Your repeated reference to "drbt" and a intensive study of the electrical side of the 48re (again the service manual) indicates that a bi-directional scan tool is required so I am working to access such an animal- seems one can exercise some of the signal pins which might prove helpful.

I will be out of town for a couple of weeks so the truck will be put on punishment until I can get back.


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Keep us posted when you get back on the project...I'm thinking you will find an easier solution than removing the unit again.  Especially with the use of the OEM spacer at the intermediate shaft...Let's see...Safe travels.



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