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47re No Overdrive (I know, I知 sorry)

Old 04-15-2019, 01:12 AM
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47re No Overdrive (I know, I知 sorry)

Hi,
I知 new to posting in this form but have read a lot through here so thank you all; y誕ll have helped a lot already.
I know this topic has been exhausted extensively on this forum and forums alike. I just had a few questions and would like some second opinions.
I just bought a 97 12 valve 4x4. It痴 got 256k on it and I got it fairly cheap as I knew OD was out. The guy I bought it from said the trans was rebuilt within the year. He said he was passing a car on the highway, the truck shifted out of od and never shifted back in. The truck shifts and pulls like it should, no hesitation, no slip. OD button on dash works. Just no OD. It doesn稚 try to shift into od.
I started with replacing the TPS (one on the truck was clearly bad and he had hacked a cheap potentiometer in).
When that didn稚 work, I spliced into the OD solenoid wire at the PCM and ran a multimeter in the cab. It read 13 volts until about 40ish mph then dropped to less than one. From what I gather from this forum, that痴 how it痴 supposed to behave. I also put the volt meter to the 8 pin plug at trans and it is getting the 5 volt supply, etc, there, so no shorts. I grounded the torque converter solenoid via a wire from the PCM into the cab while in third gear and it locked up.
From this I thought the pcm must be good and it could be the od solenoid so I dropped the pan and replaced those. While in there I checked the 3-4 accumulator spring and put a multimeter to the trans temp sensor (on the governor) and it read about 998 ohms of resistance, so I assumed it was good. Of course I also replaced the filter. The old filter and pan did have a moderate about of clutch material.
Buttoned it all up and no change. So I thought I may have used the multimeter wrong or something when testing the trans temp sensor, so I got a 1000 ohm resistor and soldered it in-line at the PCM (middle plug, pin 1. Violet wire) and no luck.
So at this point I知 willing and prepared to have trans rebuilt and beefed up a bit. I just wanted to make sure I致e exhausted all 賭uick fixes as I don稚 want to rebuild it and still have no od because it痴 an electrical/wiring issue, and because I知 strongly considering a 5 or 6 speed swap so I don稚 want to dump a bunch of cash in the 47re but I would like to be able to drive the truck while gathering parts.
So, in conclusion, my questions are~
-When trying the 1000ohm resistor trick, you do just put it in line, correct? You don稚 solder one end to PCM and the other to ground, 5 volts or 12 volts or something right?
-When reading the forums, it seems like the older model trans (RH痴 I assume), have easy bypasses. Like I致e read many times about a three wire plug on the trans that they run 12 volts too the middle wire, then run the other two in cab to grounded toggle switches to have OD and TC lock up on demand. There by no chance is an easy way to bypass and have that on a 47re is there? I know grounding out the TC solenoid wire at the PCM worked for TC lock up but it didn稚 work for OD.
-**One important thing I forgot to mention! The trans cooler lines are not great. In two spots on both the supply and return line theyre just rubber lines hose clamped to the old hard lines. The hard lines aren稚 even flared. So a gentle pull can seperate them. So they do leak a lot, could it be that the fluid pressure get high enough at the rpm that it should shift into OD that it bleeds out so much from the cooler lines it drops pressure and won稚 shift? **
-Does it seem like I did all the above correctly and interpreted everything right?
-Any other tips or tricks would be greatly appreciated.
Sorry about making such a long post about an already very discussed topic. Thank you all very much for your time!
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Old 04-15-2019, 04:47 AM
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OK, you have 2 solenoids, one for TC lockup and one for OD. They are separate.
Both get +12V from the trans relay and ground from the PCM to activate the solenoid.

Since you have already verified that the +12V are there and that the drop to 0 when the solenoid should activate - your PCM does what it should do, so no need for other resistors and stuff.

Now you will need a pressure gauge and verify that you get line pressure to the OD when it is commanded- there are 3 possible results-

A: low pressure, points towards a leak in the OD piston seal (this is quite frequent) (Can also be caused by OD clutch pack thickness and endplay not adjusted correctly during rebuild, piston gets pushed out of it's cylinder)
B: Full pressure, but still no OD- Overdrive clutch pack not correctly installed.
C: No pressure- plugged valvebody, incorrect assembly of valvebody or a dud solenoid
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Old 04-15-2019, 02:20 PM
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Thanks! That痴 very helpful. I値l run to the parts store in a bit and see if I can rent a pressure gauge.
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Old 04-18-2019, 07:00 PM
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So while hunting for a pressure gauge, I gave my local transmission shop a call and asked if they had one and how much they壇 charge. Guy said bring it down he壇 hook it up to a scanner and check the pressures via OBD port no charge. They were busy so it sat a couple days. I went and picked it up a few minutes ago. The guy I picked it up from wasn稚 the one who ran the tests and had minimal answers to the questions I had. He said it was then敗witches. Implying they were the 菟ressure switches. I pulled up a picture of a pressure solenoid and transducer and he said yup them. He said the pressures were 鍍here then all over the place.

I don稚 wanna second guess a professional, I知 sure he really is much more transmission inclined than I. I just wanted to make sure before spilling 40 more dollars of atf on my shop floor and a $70 or so on solenoid/transducer.

My question is, would the pcm still 田ommand overdrive with a bad pressure solenoid? I believe my pcm is 田ommanding because it drops volts when it should. Right? And I tested the transducer and then even bypassed it with a resistor.

Could a bad lip seal or piston seal give similar symptoms to a scanner as a bad pressure solenoid?
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Old 04-19-2019, 12:48 AM
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Well, that is why I said you would need to test the pressure for the OD with a gauge.
The only pressure sensor in the 47RE is for the governor pressure. This should be about 1 psi per 1 mph , but this pressure is only controlling your 1-2-3 shifts. It does not influence 3-4 and it does not influence Lockup.

The PCM has some inputs that it uses to regulate the shifting by the following outputs:
A: Regulating the governor pressure solenoid to achieve the desired pressure
B: Grounding the OD solenoid to pressurize OD
C: Grounding the TC-Lockup solenoid to engage lockup.

So, if you have verified that the voltage on the OD solenoid -PCM wire drops to zero from approx 12V the PCM does it's job and "commands" OD.

You can also simulate the PCM by using 2 switches to ground OD and lockup respectively.
Anyways, even if a solenoid "looks like it works" with a multi meter it can still have a sticky piston, a plugged up screen and so on- meaning a failure on the mechanical or hydraulic side of the solenoid.
There are other possible causes for the behavior your tranny shows. But I try to show you the quickest and most efficient way to find the root fault instead of just throwing time and money at it.
Now you need to know if the OD is getting pressure or not - and how much. This can not be done with a scanner, you need a gauge, a hose and the vehicle operating at certain speeds.
Think safety while doing this, driving and reading extra gauges can be dangerous. Lifting the drive axle and doing the test there is nice but exposes you to rotating parts that can kill and maim you in a blink.
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Old 04-19-2019, 12:45 PM
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Alpine, thank you! This is all very helpful and answering exactly what I知 looking for.

I just came back from a test drive with a gauge to the OD test port. 0 psi till about 43mph then 25-35psi.

So probably bad seals on the OD piston? I read somewhere it could also be a lip seal?


Should I go ahead and replace my governor pressure solenoid? 1-3rd gear is fine so probably not?

Thanks again all very helpful!
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Old 04-19-2019, 05:54 PM
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OK 1-3 working tells me that governor pressure and throttle valve pressure are good, no need to do anything about them.

The 25-35 psi when OD is commanded tell me that the PCM works fine, the solenoid works fine, but the pressure is too low- most reasonably there is leakage. Main culprit in that scenario is the OD piston seal (which is a lip seal)- the piston moves a bit and the seal lets the fluid bleed out, so you get no OD.

Now we have two possibilities-
A: the seal is damaged,
B:the piston moves too far and the seal goes out of the bore. (caused by something wrong in the OD unit- spacing, endplay etc- even got one tranny where they forgot a bearing- this did not work! surprise surprise)

Anyways, you will need to pull the OD unit. then visually inspect the OD piston, and measure some things on your OD unit and the transmission case. ( the correct values can be found in the factory service manual, less than 50$ in CD form right at your door)
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