86 Auto Doesn't Shift While in Drive? (Page 1/2)
Island198 MAY 14, 06:43 PM
So pretty much right as I solved a previous issue regarding random stalling, a new more pertinent problem started occurring. Basically, while I was out driving normally, I came to a stop. When accelerating again it felt like the car was stuck in 1st gear, and for sure unable to shift. We babied it home, and have been trying to diagnose the problem ever since. Any time I attempt to put the car in drive, it moves normally under its own power, but once at the top of 1st it just doesn't seem to want to shift out.

I have an 86 with the turbo-hydramatic 125 in it. Things we have already done to no effect include:
  • Draining the transmission fluid, and refilling with fresh Dexron (The fluid that came out was mostly clean, and didn't have much if any signs of material floating in it, but the flush was done as a safety precaution)
  • Replacing the transmission filter with a fresh one (done at the same time the fluid change was done)
  • Confirming TV cable linkage was still intact on the transmission side
  • Confirming TV cable is properly adjusted


And some facts about the issue:
  • I am still able to shift into the different gears manually. From Park->Reverse->Neutral and even the shift into Drive all operate as expected.
  • Reverse feels fine and normal
  • When manually selecting the low gearing 1 and 2, I am able to feel a difference in gearing while driving. So manually starting in 1st gear, beginning to move, and then shifting myself into 2nd gear, there is a clear feeling of shifting.
  • Shifting from 2nd to Drive makes the car feel like it is back in 1st gear, and unable to shift up again on its own.
  • Starting in Drive feels normal at first, but even at high RPMs it refuses to shift up at all on its own.


I am interested in any input or ideas anyone might have as far as the next direction to go in. Thank you for your time!
cartercarbaficionado MAY 14, 06:52 PM

quote
Originally posted by Island198:

So pretty much right as I solved a previous issue regarding random stalling, a new more pertinent problem started occurring. Basically, while I was out driving normally, I came to a stop. When accelerating again it felt like the car was stuck in 1st gear, and for sure unable to shift. We babied it home, and have been trying to diagnose the problem ever since. Any time I attempt to put the car in drive, it moves normally under its own power, but once at the top of 1st it just doesn't seem to want to shift out.

I have an 86 with the turbo-hydramatic 125 in it. Things we have already done to no effect include:
  • Draining the transmission fluid, and refilling with fresh Dexron (The fluid that came out was mostly clean, and didn't have much if any signs of material floating in it, but the flush was done as a safety precaution)
  • Replacing the transmission filter with a fresh one (done at the same time the fluid change was done)
  • Confirming TV cable linkage was still intact on the transmission side
  • Confirming TV cable is properly adjusted


And some facts about the issue:
  • I am still able to shift into the different gears manually. From Park->Reverse->Neutral and even the shift into Drive all operate as expected.
  • Reverse feels fine and normal
  • When manually selecting the low gearing 1 and 2, I am able to feel a difference in gearing while driving. So manually starting in 1st gear, beginning to move, and then shifting myself into 2nd gear, there is a clear feeling of shifting.
  • Shifting from 2nd to Drive makes the car feel like it is back in 1st gear, and unable to shift up again on its own.
  • Starting in Drive feels normal at first, but even at high RPMs it refuses to shift up at all on its own.


I am interested in any input or ideas anyone might have as far as the next direction to go in. Thank you for your time!


does this have a vacuum modulator on it? I know my 84 has a modulator and a TV cable which need to be set correctly for it to shift
theogre MAY 14, 08:21 PM
TH125 Never had a modulator.

Late or no up shift is often a Governor problem can be dirt block flow in/thru it or other problems. Governor shaft drive the VSS too but that is only for Speedo, cruise & ECM use have nothing for shifting.
Messing w/ the governor & doing wrong is a tow to trans shop & hope they still have parts for TH125c/3T40.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 05-14-2024).]

Cliff Pennock MAY 15, 03:33 AM
Is your Check Engine light working? If so, does it come on?
Island198 MAY 15, 08:58 AM

quote
Originally posted by theogre:

TH125 Never had a modulator.

Late or no up shift is often a Governor problem can be dirt block flow in/thru it or other problems. Governor shaft drive the VSS too but that is only for Speedo, cruise & ECM use have nothing for shifting.
Messing w/ the governor & doing wrong is a tow to trans shop & hope they still have parts for TH125c/3T40.



Do you think there's any benefit in removing just the governor cover to look inside for anything obvious, or is that just asking for trouble? I am in agreeance that I don't really want to mess with it directly if I can help it.


quote
Originally posted by Cliff Pennock:

Is your Check Engine light working? If so, does it come on?



My check engine light does work but hasn't come on in respect to this issue.
theogre MAY 15, 09:03 AM

quote
Originally posted by Cliff Pennock:
Is your Check Engine light working? If so, does it come on?

That has Nothing to do w/ shifting.
theogre MAY 15, 10:05 AM

quote
Originally posted by Island198:
Do you think there's any benefit in removing just the governor cover to look inside for anything obvious, or is that just asking for trouble? I am in agreeance that I don't really want to mess with it directly if I can help it.

Very likely looking @ it won't help.

Example: If dirt is blocking flow, you need to remove the governor to clean it. That sounds "simply" but if you lose or stretch the spring(s) even a little the that messes up when the weights move in turn screws w/ shifting.

While this shows "wrong" VSS, shows governor but not details. Is from TSB w/ crap in the governor from "pulse" magnet but any dirt can do same thing.


Also could be part of TV cable but not the cable itself. The valve can have problems even when the cable is adjusted right.
Many do the cable adjust wrong so if already done that...
Do Not use the gas pedal to adjust the cable. see https://web.archive.org/web...~fierocave/th125.htm

If you think the governor is bad to work on... The throttle valve is part of the valve body & all kinds of problems if taken apart then install with even "minor" errors. Like several loose balls to lose or put back wrong.

That's ignoring 30+ year old car may have other problems in the trans.
Or shifter may have problems & may not be in D but lower gears. Push button fully, don't look @ marks, Count "click" from P, 1=R 2=N 3=D etc. because the "click" are in Trans.
Cliff Pennock MAY 15, 12:49 PM

quote
Originally posted by theogre:
hat has Nothing to do w/ shifting.



Now you made me second guess myself.

It happened to me once where it would not shift out of first gear. I remember vaguely it turned out to be a stuck... TPS? (which would throw a code, hence why I asked for codes)

Anyway, something was stuck making the car think I was applying kick down.
Patrick MAY 15, 03:56 PM

quote
Originally posted by theogre:

Also could be part of TV cable but not the cable itself. The valve can have problems even when the cable is adjusted right.
Many do the cable adjust wrong so if already done that...
Do Not use the gas pedal to adjust the cable. see The ever popular TH125



I think it would be worthwhile for the OP to re-visit the TV cable. I remember when I serviced the TV cable on my '86 GT many years ago, that it was very difficult to properly adjust the "ratchet" mechanism. It was old and stiff and/or all gummed up.

[This message has been edited by Patrick (edited 05-15-2024).]

cartercarbaficionado MAY 15, 06:48 PM

quote
Originally posted by Cliff Pennock:


Now you made me second guess myself.

It happened to me once where it would not shift out of first gear. I remember vaguely it turned out to be a stuck... TPS? (which would throw a code, hence why I asked for codes)

Anyway, something was stuck making the car think I was applying kick down.


if it was a fiero it probably would have been the kickdown cable (TV) I don't think the th125 is smart enough to actually shift different from a sensor input since I know my 4t60e doesn't (vaccum modulator and a TV cable equipped trans. yes it's very very weird)