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Help me diagnose 47RE first gear issues

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Old 06-03-2018, 03:29 PM
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Help me diagnose 47RE first gear issues

I'll start with the history of this transmission:

1997 2500 4x4 with 47RE auto trans.

Trans was rebuilt by local trans shop at 163k miles, about 3 years ago.
Last year I did a fluid change, filter, governor pressure solenoid upgrade, gov. pressure sensor, output speed sensor, band adjustment.
Currently at 200k.
Trans has been operating normally since rebuild.

Last week while driving on the interstate 65mph, the oil cooler line blew apart (bad factory crimp on the rubber portion).
RPM's immediately jumped up to about 2500 when it blew, and I had to drive like that for about a minute until I could pull off safely.

Got it towed home, replaced the cooler line, and refilled the trans. Took about 8-9 quarts.

I put about 50 miles on it over the next two days and all seemed normal.
Then I took it on a longer 3.5 hour trip...All seemed normal until I got off the interstate and came to my first stop sign.
Essentially no first gear when in "D". Has to wind up to about 1800 RPM's before the truck starts to move.
But if I manually put it into "1", first gear is there.

Then I let it sit for two days.
Shifts normally when cold. Once it heats up, the first gear issue is back.
It drives fine on the highway in the upper gears, but after it warms up the first gear problem shows up.
One other issue I've noticed is that if I put it in "N" (with foot on brake in driveway), then shift to "D", the shift is a noticeably harder than before.

So Im looking for advice on what to check, how to diagnose. I need the truck daily for work, and I'm hoping I don't have to remove the tranny.
What would you look at first?
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Old 06-04-2018, 01:58 AM
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To me this sounds like a line pressure problem- slightly too high and the 47RE will go into limp mode because the governor pressure goes too high- as evident by the second gear starts.

You can either measure the pressures with a gauge, and go from there ( pull valvebody and clean everything inside) or use a resistor in the governor pressure sensor supply cable to fool the trans back into normal operation.
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Old 06-04-2018, 06:32 AM
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Originally Posted by AlpineRAM View Post
To me this sounds like a line pressure problem- slightly too high and the 47RE will go into limp mode because the governor pressure goes too high- as evident by the second gear starts.

You can either measure the pressures with a gauge, and go from there ( pull valvebody and clean everything inside) or use a resistor in the governor pressure sensor supply cable to fool the trans back into normal operation.
That's interesting. It only does this when hot, and didn't do it before the oil loss.
Do you think running it out of oil could cause this?

Im looking at the troubleshooting charts and they point to sticking 1-2 shift valve or faulty overrun clutch.

Im really hoping this is valve body issue and I wont have to dig deeper into the tranny.
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Old 06-05-2018, 03:58 AM
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Well, it could be the overrunning clutch due to the lack of fluid, or the 1-2valve due to debris or heat warping the VB.
It can also be the governor pressure sensor getting damaged by the heat.
So, IMO it would be beneficial to start measuring the pressures while driving and going from there.

The harsh engagement going into drive points towards a pressure problem, a faulty overrunning clutch or 1-2 valve would not be harsh.

Did you change the filter and check the bands when refilling the trans?

I am a rather frugal guy when it comes to repairs, so I tend to diagnose first and then repair what's needed, instead of a scattergun loaded with parts approach.
(Maybe this comes from where I am, how much I pay for freight on Dodge parts and how long I have to wait for them)
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Old 06-05-2018, 06:32 PM
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Today a very knowledgeable transmission guy suggested its pump cavitation due to oil loss. My next step is to drop the pan, examine oil and filter. Haven't had a chance yet due to work commitments.
Do you know of a good "how to" on measuring pressures? I haven't found a good one yet.
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Old 06-05-2018, 11:24 PM
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There are pressure test ports on the exterior of the transmission.



Gauge with long hose will be necessary.
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Old 06-09-2018, 07:25 PM
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OK so today I changed the filter and did a complete fluid flush (18 qts.), and adjusted rear band. There was a light coating of black "soot" in the pan, but almost nothing on the magnet.
I took it for a drive and it felt better, but still not right.
It has an intermittent, delayed, and hard down shift to first when I come to a stop. Sometimes it doesn't downshift to first at all.
Also, shifting from N to D is still hard.
So I did 5 of the 6 pressure tests outlined in the service manual. All were in normal range except the governor pressure test. Governor pressure occasionally surges to 10 psi at idle with brakes applied. And the 1 PSI per MPH was off a bit.
I then adjusted the front band but haven't road tested yet.

So the Governor pressure seems to be the culprit now, but it is a bad solenoid or transducer? They are only about a year old. Should I just replace them to rule out the possibility? What else to check next?
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Old 06-10-2018, 04:11 AM
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I'd measure the voltage from the pressure sensor and compare it to the actual governor pressure- this way you'll see if the sensor is the culprit.
While you did the fluid change- did you pull the solenoid and look for debris in the screen? Pull the sensor and look for debris pushing the "membrane" ?

But the fluctuations of more than 10psi and wrong governor pressure mean that the tranny has to freak out..
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Old 06-10-2018, 07:08 PM
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Well this morning I remembered that I already had a brand new, never installed Mopar gov. solenoid, so I dropped the pan and swapped it out and cleaned out the transducer with brake cleaner.
No more second gear starts. After my first test drive of about 12 miles, it seems to be back to "normal"....although I never really liked the way it normally feels.
When is it supposed to downshift into first?
I have always had an issue with this trans: often I have to come to a complete stop for it to drop into first. This is really annoying when I come to a light expecting to stop, but then it turns green when Im rolling at maybe 5-10 mph and I give it fuel and it is still in second. Is this a throttle valve cable adjustment?
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Old 06-11-2018, 12:53 AM
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The trans works by "comparing" the governor pressure with the throttle pressure.

So, if you got your governor pressure sorted, let's see the throttle valve settings.
Take a look if the lever on the trans starts to move the same moment as you move the go pedal.
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Old 06-11-2018, 02:44 PM
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Your issue of having to come to a complete stop in order to downshift to first is apparently common with the 47RE. My 47RE did it (still does, I think), and I have seen other mentions of it. Obviously, it's not desirable but it is apparently "typical" behavior for a stock 47RE. If you look at the Transgo and Sonnax sites, one or both of those companies address that issue in their kits.

Also, it you are trying to go by the speedometer for your 1PSI/MPH test - your speedometer may well be off a bit. I believe mine is off approx. 6%-7%. If you have access to a scan tool, you'll get better readings and be able to see what the PCM is getting from the sensor.
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Old 06-11-2018, 03:53 PM
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The usual issue is that (since the 47RE is derived from a gasser tranny) there is not enough throttle input to make the tranny downshift with a Cummins.
Hence my suggestion to first check the governor pressure circuit and then adjust the throttle valve cable accordingly.
On most trucks it makes sense to adjust the cable on the WOT stop- put the loud pedal to the metal, adjust the throttle valve cable so that the TV lever rests on the full forward stop- hence the transmission knows when you "mean it" and the other situations sort themselves by you moving the go pedal another fraction of an inch
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