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TH125C Ratio differences?

Posted: Fri Sep 06, 2019 2:49 pm
by Rettax3
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.

Re: TH125C Ratio differences?

Posted: Sun Sep 08, 2019 4:34 pm
by ifixalot
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.

Re: TH125C Ratio differences?

Posted: Mon Sep 09, 2019 10:46 am
by ifixalot
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

Re: TH125C Ratio differences?

Posted: Mon Sep 09, 2019 10:55 am
by ifixalot
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

Re: TH125C Ratio differences?

Posted: Thu Sep 12, 2019 11:34 am
by Rettax3
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: