Are there any mechanical differences between the 125s used with 4 cylinder & 6 cylinder cars? what I'm thinking, since a 4 cylinder doesn't have enough power to "hurt" the trans, that when looking for a used trans, I'd be better off getting one from a car with a 4.. OR does one have better parts? More clutches? Oppinions ? thanks

They are the same as far as I know, so are the 125's from other cars of the era.

If I had to replace a bad 125 I would put a newer th440 aka 4T60 in. It is basically a direct swap and you get 4 gears.

If it was a diect swap (AXLES), & IF it cost the same($$$), I would, but it's not. 125s are cheap (so am I) they last a long time, thats what I'm looking for, don't care how fast it goes, anything above 100 is a waste.

i was thinking gas mileage more then speed. depending on where you find one they are usually the same cost as a 125. Alot of places just have a "transmission" price and it doesnt matter what trans it is. The axles are not difficult either. But I can understand where your coming from.

Gas mileage? You want a 4T60...
If you really want a TH125c... See cave. gear ratio.
Most L4 Fiero got a 2.84 or 3.18 axle ratio. You can go up to 2.39.

TH125c is TH125c.... Engine doesn't care.
The tranny is different every couple years. Some year big changes and other year little changes. Get the newest year that you can.

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Ed Parks (I believe) mentioned, quite a few years ago, that the V6 tranny had more clutch discs in it than the 4 cylinder.
The governor will be different, which will cause it to shift at the 4 cylinder shift points. (4500-4800 or so.)
The 88 (and I think, the 87) came with a 2.84 FDR.

I would be inclined to go with the 440T4/4T60 as well.

quote Originally posted by Mike Gonzalez: If I had to replace a bad 125 I would put a newer th440 aka 4T60 in.

quote Originally posted by Lou6t4gto: 125s are cheap (so am I) they last a long time, thats what I'm looking for, don't care how fast it goes, anything above 100 is a waste.

quote Originally posted by Mike Gonzalez: i was thinking gas mileage more then speed.

Mike Gonzalez's comment about mileage versus performance is correct; the 4T60's fourth or overdrive gear, drops RPMs for better mileage than the TH125 can muster. However, contrary to popular belief, there essentially is almost nothing more "performance-oriented" about a 4T60 than a TH125 because the numerical differences between their first three gear ratios are trivial.

That said, I can empathize with your situation, Lou6t4gto. When it was time to replace my transmission, I opted for another TH125 because my 3.4L '86 is a daily driver, and I couldn't afford to have anything more than minimal downtime with it. If I'd had more time, and wasn't constrained by it being a "commuter car," I might well have been willing to find and install the special axles needed for a 4T60, maybe not because of improved mileage per se, but also because its lower RPMs in overdrive probably would have made long trips at highway speeds more relaxing.

WHAT Year?model Fit for the overdrive?? NON electric ? I saw a mid size Buick in the wrecking yard yesterday, Totalled from The REAR. If thats a Non Electric, Maybe thats a good choice for $150 ! (have to look at the mileage, but obviously it was working.) So, I would have to take the AXLES with it ?

Copied from Wikipedia :

Turbo-Hydramatic 440-T4

A breakdown of THM440T4 is: Turbo HydraMatic Model 440 - Transversely Mounted - 4 Speed Fully Automatic transmission

A 4-speed version of the 125 was created for the 1985/1986 GM C platform (FWD)/GM H platform (FWD) cars, the Turbo-Hydramatic 440-T4. Many parts were identical to the 125, though it was generally stronger and included an overdrive fourth gear. This transmission was first used in GM's 1985 Buick Park Avenue, Oldsmobile 98, and Cadillac Deville. In 1986, after switching to FWD, the Buick LeSabre, Oldsmobile Delta 88, and later, the Pontiac Bonneville also used this transmission. A special strengthened F-7 version was also used for the 1987–1992 Cadillac Allanté and 1989-1990 Pontiac Turbo Grand Prix.

One unique feature of this transmission is its use of both a modulator valve and a throttle valve (TV) cable. Most transmissions either use one or the other to control shift points and shift smoothness. On the Turbo 440-T4, the TV cable exclusively controls the shift points, while the modulator valve controls the shift feel. This feature makes it very easy for a home, "shadetree" mechanic to adjust the transmission shift points with minimum effect on the shift feel.

The 440-T4 was originally slated to be used with downsized C body cars for 1984, however, issues with failures led to introduction being delayed until 1984 for the 1985 model year.

The 440-T4 was later renamed the 4T60.

The electronically-controlled 4T60-E was introduced in 1991. It would become the basis of the GM 4T65 transmission, still used today.

A heavy-duty version, the 4T60 HD was used for the 1989-1990 Pontiac Turbo Grand Prix.

Applications:

4T60
1988-1994 W platform
1985-1993 H/C platform
1985-1993 A platform
1988-1990 Buick Riviera/Reatta
1985-1990 Cadillac models
4T60-HD
1989-1990 Turbo Grand Prix

the only other thm125c i know of is the awd one in the 88(?)+ 6000's. unless those were the four speeds.

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project 34, This car is going to be my wifes go to work, go to the store, IN CITY car, will very seldom if ever see the interstate, the only reason it's getting the 3.4 over the 2.8 is: I have both,& they cost about the same to rebuild, & I will drive it now & then :-)

quote Originally posted by Lou6t4gto: project 34, This car is going to be my wifes go to work, go to the store, IN CITY car, will very seldom if ever see the interstate, the only reason it's getting the 3.4 over the 2.8 is: I have both,& they cost about the same to rebuild, & I will drive it now & then :-)

Under the expected driving conditions you've described, I don't see a compelling reason for you to move away from the TH125 in favor of a 4T60.

That aside, hopefully your wife and you will enjoy (as I have) the noticeable increase in low-end, "in-city" torque that can be afforded by a 3.4L swap, as well as the day-to-day reliability I've enjoyed with my own 3.4L swap.

Here's a link that I've kept that lets you see what other vehicles use a given transmission...

Auto Tranny Xreference


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RickN
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[This message has been edited by RickN (edited 12-24-2009).]

quote Originally posted by RickN: Here's a link that I've kept that lets you see what other vehicles use a given transmission... Auto Tranny Xreference http://tinyurl.com/yb5sqel

As of this writing, the above link apparently won't work without getting rid of the "s" in "https" --- leaving this:
http://www.drivetrain.com/p...html#CHEVROLETGMCGEO

***Edited to acknowledge RickN's correction of the link.***

[This message has been edited by project34 (edited 12-24-2009).]

quote Originally posted by project34: As of this writing, the above link apparently won't work without getting rid of the "s" in "https" --- leaving this: http://www.drivetrain.com/p...html#CHEVROLETGMCGEO ***Edited to acknowledge RickN's correction of the link.***

Thanks, I was probably still working on the edit when you read it. I had a hard time figuring out the problem.

Those are GREAT LINKS ! THANKS

The one difference not mentioned here is that V6 trans had a larger boost valve to handle the increased power of the V6. Internally they are the same(year for year),aside
from gearing and govenors. Unless you are into swapping a few parts around(you will have to rob a V6 VB for the boost valve-not availible separately),I'd opt for the V6.
The gears and gov will better match your aplication.
Marc