Thread: Overdrive Issue

Hello folks,

It has been a while since I have posted anything on here, but I am in desperate need of some help today. Let me give you the car specs first:

1995 Pontiac Grand Prix
3.1 Liter V6
Miles: 225,000
Transmission: (salvage yard) 4T80E

The issue I am having is that my mother had a mechanic put the transmission in the car about eight months ago or so. My mother said that the car was running great, but the gas mileage did not seem to be where it needed to be. I actually took the car to work with me, which was two hours or so from where she lives, so that I could take a look at it in my friend's shop. I noticed on the way up that it was not going into overdrive. The transmission does not slip, and it pulls strong. I can do a manual shift through: first, second, and third fine. When I go to drive the RPMS never change. It doesn't even try to go into overdrive, almost like it's not even there. I have found a two wire plug on top of the motor that was left loose over by the alternator. I don't remember the exact color of the wires, I remember one was yellow. The plug length is probably just over a foot long, and the end is red in color. I have looked at several wiring diagrams trying to find where this creature goes, and what it is, but no luck. To me it's almost like lockup is not getting the 12v it needs to engage.

Here are some fluid specs on the tranny:

Color: Light red
Smell: Not burnt
Level: full at idle

Can someone point me on what I need to do to start diagnosing the issue. I really think the transmission is okay. It pulls really strong, and doesn't slip.

Thanks,

littlekatfish2003

Rebuild tranny. You lost the splines on the 4th gear shaft. Or just drive it in 3rd.


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Is there a diag that I can do to see if it's the 4th gear splines, before I go through the trouble of pulling the tranny and going through a rebuild?

Brandon,

Did you have to unbutton the cradle a bit to get to spline? I have never been in one of these transaxles before. I have been in several transmissions, never a transaxle. Think you would have time to give me a run down?

Thanks,

littlekatfish2003

Thank you

Yes. He does describe losing the 4th spline's by his symptoms.


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When I will get home today, I will take a picture of the plug and the color of the wires that I have located by the alternator that is currently loose, which I have no idea what it does, or where it belongs. I have looked on several wiring diagrams. I cannot find what it is or where it goes. I'm not to sure that it may have something to do with the lockup getting the 12v it needs to engage. I have verified that it is a 4T60E. The 4T80 was not available in this car yet at the time it was produced. When I cruise down the highway in it, it drives really well. I have: first, second, and third. It never even attempts to go into 4th gear. The RMPS stay at about three grand doing 65, they never drop and come back up like it is slipping in and out of overdrive. It never attempts to go into it in the first place. Any other thoughts or ideas? Really looking on where to start. The car is OBD 1 and isn't even throwing a code for it. No check engine light or anything.

Okay I got my friend to hook his scanner up to the car this last weekend. I don't remember the exact code, but there was a tranny code. He said that the computer doesn't know what gear the car is actually in. He said it is only reading first and second according to his scanner. He said to replace the range sensor on the tranny and it should fix it. I have been doing some research on this range sensor, I am not sure if it is actually in the tranny, or an external part. I found the neutral safety switch, which is the switch the shifting cable runs into I believe. Do you all have any: thoughts, questions, or ideas? If someone knows where this sensor is, please point me where I need to dive-in to get to it. I also need help finding the part. I called O'reilly's, they couldn't even order the part. Any help would be great.

Thanks,
littlekatfish2003