47re No Overdrive (I know, I’m sorry)

Discussion in 'Engine & Performance' started by Name, Apr 14, 2019.

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  1. Name

    Name Junior Member

    Age:
    24
    Posts:
    2
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    Joined:
    Apr 14, 2019
    Location:
    Alabama
    Ram Year:
    1997
    Engine:
    12 valve
    Hi,
    I’m new to posting in this form but have read a lot through here so thank you all; y’all 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’s 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’t 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’t 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’s how it’s 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’m willing and prepared to have trans rebuilt and beefed up a bit. I just wanted to make sure I’ve exhausted all “quick fixes” as I don’t want to rebuild it and still have no od because it’s an electrical/wiring issue, and because I’m strongly considering a 5 or 6 speed swap so I don’t 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’t 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’s I assume), have easy bypasses. Like I’ve 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’t 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’t 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’t 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!
     
  2. Name

    Name Junior Member

    Age:
    24
    Posts:
    2
    Likes Received:
    0
    Joined:
    Apr 14, 2019
    Location:
    Alabama
    Ram Year:
    1997
    Engine:
    12 valve
    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’d charge. Guy said bring it down he’d 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’t the one who ran the tests and had minimal answers to the questions I had. He said it was then”switches”. Implying they were the “pressure switches”. I pulled up a picture of a pressure solenoid and transducer and he said yup them. He said the pressures were “there then all over the place”.

    I don’t wanna second guess a professional, I’m 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 “command” overdrive with a bad pressure solenoid? I believe my pcm is “commanding” 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?

    Before I drop the pan I will still hook up a gauge. Would a bad pressure solenoid cause pressure to read low at the 4th gear port?
     

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