quote Originally posted by DandRauto: What or how do you get and know the TV adjustment is right. Assume it's not the same as in the factory service manual? i guess?

There are at least three factors that determine whether the TV cable will correctly actuate the throttle valve or not:
TV cable position at idle; this is set by the "TV Cable adjustment" procedure in the shop manual
TV cable position at WOT; the throttle cam must pull the TV cable far enough to actuate the throttle valve enough to raise the line pressure enough to deal with the torque the engine makes at WOT.
TV cable position at intermediate throttle; the throttle cam must pull the cable in such a way that the line pressure rises as fast or faster than the torque the engine is producing. If the cam is positioned such that the TV cable moves very little while engine torque rises significantly, the transmission will have problems, even if the cable position is right at WOT.

So you see, even if the TV cable adjustment procedure is followed correctly, if the throttle cam isn't exactly like stock, then the transmission could still be in a world of hurt.

[This message has been edited by Will (edited 11-06-2009).]

Here's some info you can use about ratios I posted some time ago. I rebuilt 2 or 3 125s behind turbo V6s and inculded a shift kit but despite the firmer shift they didn't hold up long and would start to slip 3rd gear when warm and that was with a properly adjusted TV cable which manifests as early shifts if it's too loose or late shifts if it is pre-loaded too much. I believe it's the early shift misadjustment that will burn up the tranny quick given my observation with that condition in a 700R4 with a tranny temp gauge.

https://www.fiero.nl/forum/A...060811-2-070109.html

im sure its been said a lot, but the TH125C is WEAK. if my 88 duke (pontiac 6000) could break it, then its just trash.

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First LX9 Fiero GT, 1987 | My Fiero Fuel Economy | MPG Display for OBD I
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If you can't fix it with a hammer, you've got an electrical problem
Fiero's are people too. We pay just as much attention to them, if not more than our loved ones
screw paying those bastards. im not going to become rich by paying for things.....

quote Originally posted by americasfuture2k: im sure its been said a lot, but the TH125C is WEAK. if my 88 duke (pontiac 6000) could break it, then its just trash.

Old worn high mileage 21 year old transmssons are certainly weak. Try a freshly built high performance TH-125H from Jims Performance Transmissions in Eaton Rapids MI and see if you can break it with a Duke.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, 3.4" Pulley, N* TB, LS1 MAF, Flotech Exhaust Autolite 104's Custom CAI 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by americasfuture2k: im sure its been said a lot, but the TH125C is WEAK. if my 88 duke (pontiac 6000) could break it, then its just trash.

That's what I been saying, The TH125c is a Weak transmission, The thing was built in the 80s to support underpowered 4cyls, Getting one rebuilt or anything is a big waste of money, When you can simply go out and just get the transmission that came with the engine, I would trust a high mileage 4t65E HD or a 4t65E(with over 260k miles) over a brandnew preformance built TH125C any day of the week

From all my experiences with transmissions, the TH125 can be built to handle higher HP. Never worked for me though. Had mine rebuilt 3 times and $2600, drove over 2000 miles from AL to MI several times. Finally a local shop got it right which a Northern pro racing shop which I won't mention didn't. I believe I could have had a 4T60 beefed up with 65 parts for what I spent on a TH125. My 4T60 is one my best upgrades. Wish I had done it sooner. Also the 33/37 sprocket sets are not interchangable between the TH 125 and 4T60.

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85 GT 3.4
14.9 @ 90 1.9 60' Old TH125/3.06
Unknown New 4T60/3.42

quote Originally posted by Lilchief: From all my experiences with transmissions, the TH125 can be built to handle higher HP. Never worked for me though. Had mine rebuilt 3 times and $2600, drove over 2000 miles from AL to MI several times. Finally a local shop got it right which a Northern pro racing shop which I won't mention didn't. I believe I could have had a 4T60 beefed up with 65 parts for what I spent on a TH125. My 4T60 is one my best upgrades. Wish I had done it sooner. Also the 33/37 sprocket sets are not interchangable between the TH 125 and 4T60.

O yes they are. http://spacecoastfieros.com.../440-4T60/index.html "The final drive and the sun gear from the TH125C will work in the 4T60. The ring gears of the two transmissions are different and will not interchange. This is not a problem since the planetary gears will fit either ring gear unit. Keep the 4T60 ring gear and have your transmission rebuilder assemble it to the TH125C sun gear and final drive."

I was talking about the chain drive sprockets 33/37 . I have had both in my hands, one from a TH125 and the other from a 4T60. They were both made for the good chain, they made a not so good chain also. The sun drive gear set may very well be interchangable, but not the chain drive sprockets, been there done that.

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85 GT 3.4
14.9 @ 90 1.9 60' Old TH125/3.06
Unknown New 4T60/3.42

quote Originally posted by fieroall: Here is the pick. The chain is the coolest thing I've seen yet. Hope installation goes smooth. I will take picks.

Have you any updates to share with us regarding your project?

I'm very much hoping that a termination of your project hasn't been necessitated by an unanticipated change in plans.

Besides, I still can't find on-line the AC Delco part number you cited for the chain (# 8660099). Did you obtain it in an AC Delco parts store (even though it's not on AC Delco's website), or did you obtain it someplace else?

Hey 34,

No haven't quit my project. I'm just in the process of rebuilding the engine I'm using which stalled me back a bit. I should be back into it in a few weeks. I also ordered a TransGo shift kit and am contemplating using a 3.33 tranny from an 87 car. If I can find one. I will update as soon as I have some progress.

As for the part # I called my local transmission parts guy and told him to find the sprockets and match up a chain for it to go into my TH125. The chain he got me is a BorgWarner Morce Hy-Vo Chain Part # A84700A (125C/440 84 - UP). Hope this helps.

[This message has been edited by fieroall (edited 11-11-2009).]

I very much like the way you've attempted to steer this thread, fieroall, which, after all, is your thread in the first place.

More specifically, you started your thread with one inquiry on your part, incorporated the responses you'd received from that and your other inquiries, and you'd then formed what essentially now is becoming a documented "build thread" on the sprockets and chain modification for a TH-125 automatic transmission.

IMHO, you've exhibited a commendably very helpful degree of specificity (exemplified by your providing part numbers and pictures) which I've just not found in earlier threads in regard to this topic.

I suspect that you, the former "student" with regard to this gearing improvement, may soon become the "teacher" on this topic, and I'm sure I'm just one of several who very much will look forward to that.

Accordingly, please keep us posted on your project as it develops, fieroall.