TH125C: How do you make more pressure??

[turbobuick88]

So I would like to keep the 3 speed TH125C but it will die eventualy with the 3.1 Turbo, unless I can modify it to make more pressure. Dose anyone know how to modify them to make more???
This was originaly posted on my main forum A-body.net:


Quote Originally Posted by Turbobuick88 View Post
It all looks great! cant wait to see what it can do after a tune!
so David is there any way to really save the TH125s 2 gear band? I would kinda like to keep the 125(I have one with 30K) instead of swapping a 4 speed (is it alot of work?)
I think there IS a way to make the 125C hold up, but I haven't found any documentation on it. I know there are some Fieros with Chevy V8-350 engines running 125C's that hold up. A turbo 3.1 is about equal to a good solid 350 Chevy. There isn't a shift kit (that I have seen) that gives more pressure when needed. I beleive certain people have figured out modifications, but they are keeping the info for themselves.

I would need to study the 125C valvebody, and see if I can determine a way to give more charge pressure to the clutches and bands without causing the shifting points to be delayed. There is probably one or 2 springs that could be changed out and accomplish this.

If anyone has any info please post it up! Thanks!!

[1988GTU]

What I am about to say is possibly going to save you time and money.

Dump the 3 speed and go with something else. You'll need a piggy back system such as FAST or e trans controller but in the end, you'll end what you want and that is reliability with performance!

I do not recommend keeping the 3 speed at all for performance! Any one that tells you it can be built or become bulletproof is on crack rock!

[Superdave]

Here is a built one for sale...

http://www.v6z24.com/jbodyforum/completely-rebuilt-performance-t125-t116537.html

[davida1_hiwaay_net]

What I am about to say is possibly going to save you time and money.

Dump the 3 speed and go with something else. You'll need a piggy back system such as FAST or e trans controller but in the end, you'll end what you want and that is reliability with performance!

I do not recommend keeping the 3 speed at all for performance! Any one that tells you it can be built or become bulletproof is on crack rock!

This is true. The ratios in it are not good for aceleration. The 4 speeds have a lower first gear, as well as that nice 4th gear for cruising! And the Reverse on the 125C is a joke. Seems like the engine has to rev halfway to redline against the torque converter just to back up a hill! Comparing it to my 4T65E car, i always think I am hung up on bushes, running over something etc. with the 125C backing up a hill in Reverse!

I have talked to Turbobuick88 about the 125C trans before. He's been watching my 1988 Olds Ciera XC Turbo build thread. I don't want to change the transmission on that car at this time. I want to see what I can get out of it as-is, with only turbo, injectors, tune, and exhaust changes. If by a simple spring or vavle change in the 125C, it can simply "not fail" (nothing said about actual performance - just lack of immediate burnout) this would be worthwhile for me.

With my Ciera XC Turbo project, (125C and stock 2.8 ) the 120,000 miles, stock 2.8 will not withstand a huge amount of boost. Turbobuick88's car will have a 3.1 LG5 engine that will make far more HP than this. I don't see a 125C being a good choice for anything other than a get-by until he can build something better!

On my other car (making over 400 engine HP) I swapped in a 4T65EHD, using stand-alone GM controller with Ostrich emulator. It shares only the TPS signal and the engine speed signal with the 7749 Code59 engine ECM.

David

[1988GTU]

I made as little as 10 lbs on a 2.8 and it smoked a 100k miles trans (3peed) . Ive had a few stock built zero miles ones and it still couldnt take it. It only got worse with more boost. I had a supposed bulletproof pos built, didnt last a day.

Its not a trans for anything more than stock hp/tq