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tywilson

Dodge Truck A518 4-speed Automatic Won't Go Into Overdrive

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My 1990 Dodge Ram 250 4x4 has overdrive, and it quit working on me.  I still cannot figure out why.  However, I was doing some research on the transmission for the possible lube issues you talk about in the RWD Chrysler transmission article at the magazine site. You describe Sonnax upgrades, I called them, and they were very prompt in calling me back.  They were busy and told me to consider putting in a manual valve drop-in and a line to lube pressure regulator—all bolt in, no drilling, basically plug and play.  Will this help my overdrive issue?

 

Ty

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Hi, Ty...For those unfamiliar with the Sonnax upgrades for RWD Chrysler transmission on Jeep and Dodge Ram trucks, see my article: http://www.4wdmechanix.com/Survival-Upgrades-for-Jeep-and-Dodge-Ram-Automatic-Transmissions.html.  I'm very pleased with the Sonnax upgrades for our Ram 3500 48RE transmission, which include the manual valve, line pressure valve, the detent ball/sleeve and a piston upgrade—each without removal of the transmission or a major teardown...If you want your RE or RH transmission to survive, read the article at the "Automatic Transmission Workshop"!

 

Your A-518 automatic is the first 727 Torqueflite-derived RWD Chrysler platform.  Chrysler introduced the A-518 in 1988 and used it through 1996 on some applications.  (42RE and 46RE were essentially the replacements for the A-518 in trucks.)  The A-518 has many similarities in design and parts layout to both the A-727 Torqueflite 3-speed and the later RE 4-speed overdrive transmissions.  Jeep 30RH and 32RH transmissions are also similar, but like the lighter A-500, their platform is the Chrysler 904/999 three-speed.

 

The A-518 and later RE transmissions have the 4th gear overdrive built into the transmission unit and cases, and control for overdrive is solenoid based.  As for stamina, the A-518 four-speed overdrive became a muscle car retrofit when built to performance standards.  This replaces an A727 three-speed, modifying driveline length and the rear motor mount to fit.

 

JVX Racing specializes in this conversion and makes a range of upgrades for the 904/999, 727 and overdrive derivatives like the A-500 and A-518.  The JVX catalog will be very useful for reference, Ty, and they also have a manual or controller shifting mechanism to replace the stock shift-to-overdrive system:  http://jvxracing.com/jvxcatalog.pdf.  Download the catalog to better understand the performance uses and upgrades for your transmission and modifications available.

 

All of these overdrive derivatives rely on the stamina of the original A-727 or 904/999 three-speed designs.  Overdrive becomes the wild card, yet these units hold up better with each new design iteration over the years (42RE through 48RE in Dodge Ram trucks).  Our 48RE is allegedly the "best" of these units, the last iteration, anyway, and late enough to have many of the weaknesses found in earlier RE overdrive units worked out. 

 

In your case, you have a "factory" A-518 installation, with all of the stock controls for overdrive.  Here is the "factory" explanation for the 3-4 Shift on a similar 42RE transmission.  I have bolded the points of interest to your problem, Ty.  This should help clarify:

 

"3-4 SHIFT SEQUENCE...The overdrive clutch is applied in fourth gear only. The direct clutch is applied in all ranges except fourth gear. Fourth gear overdrive range is electronically controlled and hydraulically activated. Various sensor inputs are supplied to the powertrain control module to operate the overdrive solenoid on the valve body. The solenoid contains a check ball that opens and closes a vent port in the 3-4 shift valve feed passage. The overdrive solenoid (and check ball) are not energized in first, second, third, or reverse gear. The vent port remains open, diverting line pressure from the 2-3 shift valve away from the 3-4 shift valve. The overdrive control switch must be in the ON position to transmit overdrive status to the PCM. A 3-4 upshift occurs only when the overdrive solenoid is energized by the PCM. The PCM energizes the overdrive solenoid during the 3-4 upshift. This causes the solenoid check ball to close the vent port allowing line pressure from the 2-3 shift valve to act directly on the 3-4 upshift valve. Line pressure on the 3-4 shift valve overcomes valve spring pressure moving the valve to the upshift position. This action exposes the feed passages to the 3-4 timing valve, 3-4 quick fill valve, 3-4 accumulator, and ultimately to the overdrive piston. Line pressure through the timing valve moves the overdrive piston into contact with the overdrive clutch. The direct clutch is disengaged before the overdrive clutch is engaged. The boost valve provides increased fluid apply pressure to the overdrive clutch during 3-4 upshifts, and when accelerating in fourth gear. The 3-4 accumulator cushions overdrive clutch engagement to smooth 3-4 upshifts. The accumulator is charged at the same time as apply pressure acts against the overdrive piston."

 

All of the information is useful; however, your problem is likely localized to the control switch, the solenoid and the wiring interface between these devices and the PCM (powertrain control module, also called the "computer", ECM or ECU).  So, troubleshooting should involve the control switch for overdrive, the solenoid and the wiring.

 

Let me know if you need procedures for testing...Pleased to help here.

 

Moses

    

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I recently overhauled a 42RE in a 96 Jeep Grand Cherokee rebuilding the overdrive section with A518 internals and the forward section using TF999 friction discs (incl. Kevlar bands) - im having the no 4th gear issue (prior 2 the overhaul the previous trans failed after the overdrive grenaded and shattered the overdrive planetary) after the overhaul (did field strip the valvebody and installed a new TCC/shift wiring harness and still no overdrive (did the KOEO and pulled no codes)

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motrosepatriot...I had a lengthy discussion with an RE owner around his replacement of the overdrive unit.  See if this exchange helps:

Let us know what you find...

Moses

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during the 42RE overhaul I used the Sonnax parts (exc the detent check ball since the existing bore was not worn out) and replaced the O/D-lockup solenoid pack (also swapped the gov pressure manifold using the aftermarket version using a 4L60E EPC solenoid); during the valvebody field strip the 3-4 spring was intact and undamaged but during a test drive the OD light did not flash (here's what im experiencing - when hittin the OD off 2 light up the OD lite the TCC (converter clutch) unlocked and locked and when hittin the switch again its doing the same (unlock and lockup) and still no codes (im concerned that its the OD dash switch asm - did a fuse inspection @ the junction block where no blown fuses)

also the TV cable is adjusted 2 spec; during the recent overhaul back in March 2017 the O/D piston housing (bolted 2 the trans case) - the internal filter (located in the OD piston) was sprayed with carb cleaner and it was not plugged up (this filter is the one I would not pull out since a YouTube video detailed a repair of a similar 42RE when the filter is out (cause is no overdrive)

regarding the O/D housing (which is a 2WD) the clutch pack was upgraded 2 48RE/A518 specs (including a TransGo overdrive spring assembly (800 lb spring), twin groove OD direct clutch drum (10 discs), A518 5 pinion planetary, and the 5 disc upgrade (overdrive clutch)

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Many do the G.M. solenoid change, which usually does not impact the issues you're having. If your clearances are correct (my reason for drawing attention to the 48RE overdrive unit installation/discussion and the O/D piston spacer fit), this could be an O.D. switch circuit or solenoid issue.

You could have an electrical issue at the switch or the overdrive solenoid.  Test sequences for the O.D. switch can be done with a simple voltmeter check.  If voltage is available when needed, I would perform a transmission pressure check for overall line pressure at various throttle settings and the pressures during the 3-4 upshift at various throttle settings.

I'm not a fan of replacing parts without performing tests first.  This is especially true if the system did not have problems before and now has these symptoms.  The Sonnax upgrades beg the question about line pressure.  Line pressure is adjusted at the valve body pressure regulator spring, confirming the setting with a hydraulic pressure test.  I would also test the Throttle Position Sensor (TPS) voltage, as the TPS voltage signal, like the TV cable adjustment, can affect the 3-4 upshift.

Here are some potential causes for a 3-4 upshift malfunction on the 42RE/44RE transmissions.  I would rule out each of these possibilities before another teardown:

42RE-44RE 3-4 Shift Issues.pdf

In ranking order, I would check the O.D. switch circuit and wiring, the O.D. solenoid function and the hydraulic line pressure at various throttle settings.  Adjusting line pressure at the valve body is often necessary after valve body and solenoid changes.  Make sure your transmission cooler works properly and is not restricting fluid flow or creating back pressure.  If you installed the Sonnax manual valve, you now have fluid pressure flow to the torque converter and through the cooler in all gears, Neutral and Park.  Details from my article at the magazine (http://www.4wdmechanix.com/Survival-Upgrades-for-Jeep-and-Dodge-Ram-Automatic-Transmissions?r=1):

Sonnax kit

[Illus. 8: Sonnax also provides a manual valve that allows fluid charging of the torque converter in Park position. These Chrysler transmissions do not charge the converter or transmission cooler when in Park; this delays gear engagement, especially after parking for longer periods. The Sonnax manual valve will help prevent front pump bushing failure, the result of fluid starvation in Park.]

According to Sonnax, you should remove the OEM anti-drainback valve when installing the Sonnax full-pressure manual valve.  If the factory anti-drainback valve has been left in place or the cooler is restrictive, back pressure may be boosting pressure within the system.

Let us know what you find... 

Moses

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