TH125C Ratio differences?

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Rettax3
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TH125C Ratio differences?

Postby Rettax3 » Fri Sep 06, 2019 2:49 pm

Okay, yes I spent some time 'Search"ing, not finding much relevant to my question though -still some interesting topics come up here :good: . I suspect it is here somewhere, but really, is fresh posting on this forum a bad thing now?

Here is my question, and I hope someone on here with knowledge and an interest in sharing such would like to chime-in:

Is there a difference in the gear ratios in the TH125C 3-speed automatic from year-to-year or from engine-to-engine? Specifically, would a '90 3.1 utilize the EXACT SAME gear ratios as, say, an '88 2.0? I know different GM vehicles got different ratios, but did Chevy bother to use a different FDR for the smaller 4-bangers?

Part two to the question is torque-converter stall-speed, any difference there?

I've glanced outside the forum here too, and found data suggesting both the '90s 3.1 and the older 2.0 used 3.18 ratios, nothing concrete though, again, not making it a career to search for this.

:beer: Thanks.


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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ifixalot
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Re: TH125C Ratio differences?

Postby ifixalot » Sun Sep 08, 2019 4:34 pm

From what I remember, when I was looking to replace the th125 in my mini van, there are differences in both the final axle ratio as well as the stall speed of the torque convertor. The junkyard had to look up and cross reference a trans that might work for my mini van. I wound up just rebuilding
mine since all they had was junk.



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ifixalot
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Re: TH125C Ratio differences?

Postby ifixalot » Mon Sep 09, 2019 10:46 am

Here is a link to another forum that has a list of ratios and stall speeds for various models. It only goes up to 1988 but I hope you find it useful.
https://www.a-body.net/forums/showthrea ... nterchange



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ifixalot
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Re: TH125C Ratio differences?

Postby ifixalot » Mon Sep 09, 2019 10:55 am

Here is another link with more info. Scroll way down to find the list of later model units.
http://www.j-body.org/forums/read.php?f ... 99&t=26499



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Rettax3
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Re: TH125C Ratio differences?

Postby Rettax3 » Thu Sep 12, 2019 11:34 am

Thank you, this is about what I was looking for (I think so anyway, the photo-bucket images are all blurred-out right now for some reason -I never understood why people used the third-party hosting, I guess I just didn't get into it enough to see the advantages :unknown: ). I remember your van's tranny issue, and was hoping you would chime-in, I know you have direct knowledge on these units. :good:


1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26


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