Hello guys.
Last winter i modified my automatic t 125 transmission.
The goal was to reduce the rpm at high speed.(speeding for me is 60 mph.).
Even with the 15 inch. tire, the rpm at 60 was over 3400 . I hate that......
I have a 2007 pontiac g6 and at that speed, the engine was running well bellow 2000 rpm.
So i decide to open the tyranny. I remooved the engine and transmission at the same time.
The car code for my transmission was f 75. This indicate a diff.ratio at 3.18.
That mean that i have a 33/37 at my chain drive. I simpely put a 38/32 in place.
This process will change the FINAL ratio of the transmission.38/32 is the maximum final drive that you can have..
I rebuild completely the rest of my transmission while i was in there. It is a cheap way to be sure that your transmission will
remain in place for a long time. It cost me 500$ for the parts and seals. I changed the tcc solenoide and the oil pump also.
I instaled my new 3.1 engine with the freshly rebuild transmission some weeks ago and WOW....the engine is running almost
1000 rpm lower now . The engine spurr like a kitten at 2500 at 60 mph. (100 kmh.) Great improvement. The man is happy.
Thanks to read this.
Alain

Sounds awesome! Is the torque still decent? I plan to do a 4 speed swap for mine.

The torque does not change much. Of course at low speed went the TCC goes in the engine drop to 1400 rpm. At this time the torque is not that good.
But at 60 or 70 mph, the difference between the old and new transmission ratio does not affect the performance much.
In fact the final ratio is the same than with the 5 speeds standard transmission.
With my previous z 24 1987,with 5 speeds trans, at 60 mph the engine was at 2500 rpm.
Same as with my automatic now.

I have read that the FWD GM trans axles have a couple dozen different ratios by changing that drive chain , but your the first I've heard that went in and swapped it. The V-6's have more torque to pull along at taller numerical ratios than their 4 cyl. cousins can. It sounds like you have plenty of Automatic Transmission know-how / experience since you rebuilt your own and replaced the oil pump and TCC Solenoid. Just curious if this change threw off your Speedo Accuracy ?? Very Nice results!! - "Never Underestimate a 1st Gen!!"


Josh have you ever gotten any closer to reaching your project of a 4speed Auto ??? Remember you were trying to find a pre-electronics version.



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Thank's guys for your comments.
Yess,a lot of peoples talked about this modification but it
seem like no one ever try it. Even on the Fiero group they talk a lot
about the possibilitys of this modification but no one seems to have it done.
Maybe because it does not interested people to lower the performance of their cars.
Yes,there is some in between ratio that you can do. I chose the most dramatic ratio change.
It does not change the speedo accuracy because the vss.is reading the speed after
the final ratio of the transmission. In fact the vss. read the speed at the output shaft . So
every differential and gears ratio combinations should use the same vss. I also installed a toggle switch
to cut the tcc. as i want. So at middle speed i can switch on or off the torque converter.
I also think that the car will burn less gaz. Of course not if i am able to run the car faster.........
I encourage all of you guys who want to do this modification to have a more corfortable car
at hight speed.
Alain

I did Orlen. My dad has technical book on the 4T440 from 88-98. Apparently 88-89 is non electronic and I discovered that a Beretta and Corsica have the same width chassis as a cavalier.

That is a step ahead for your situation.Good info and as long as it works in your favor great.I myself have a manual 4 and pretty (staying as it is) bc I have always got consistent mpg and the torque pull is wayy better to me as it is.That is pretty neat to be able to understand the how to do as I myself never dove into a trans to that degree.Just clutches and simple things.

I'd love to do something like that, but with a 2.0 4 cyl powerplant and driving a majority of my miles around town and up & down hills, I think the car wouldn't be able to get out of it's own way...




~ Mike ~

Oh yess Mike, this modification is a v 6 option only.
Alain