Ive done a lot of searching on these tranmissons and hopefully this Saturday will be picking one up. Within the next year or two I will need to replace/rebuild the TH125 in my 87 GT so I figured I might as well replace it with a overdrive model. Now I also plan on doing a 3.4 swap within the next couple of years (or when my 2.8 decides it). Would having a 3.4 differ on how I would build it up verses having a 2.8? For starters are there any performance gains in just swapping out these transmissions? What would be the ideal gearing for speed? (Mostly 0-60 speed as this car is only a "fun" car and very rarely makes it on the expressway or over 60 mph.) Keep in mind fuel economy dosent matter in the slightest degree as I maybe only fill the car up a couple times a year.

Im sure more questions to come,
Thanks,
Jason

Jason, I did a 4T60 swap into my 88 Formula with the 3.4. It was great. I used a 3:33 ratio trans from a Buick Reagle. Lots of go at the stop lights and great economy on the highway. 3:33 is the stock ratio for the 125 in 87 also. The overdrive gear on the 4T60 was the best thing for it.

Thanks for your input foxgapfiero. By just switching from a 3.33 stock tranny to a 4 speed 3.33, did the car come off the line better?

Jason

I could be wrong, but I thought it did. Mind you, this was with a 3.4 installed.

If I am not mistaken, the 4T60 has a lower first gear than the 125, that's why there's more "woohoo!" off the line.

The specs I've read show the TH440 and TH125 with almost the same gear ratios in 1st through 3rd. But of course, the TH440 has a fourth gear. The trick is to find (or build) a TH440 with the lowest-geared final drive you can get (something like 3.73 with the right chain sprockets), which will improve acceleration in 1st-3rd gears. Plus, 4th will still be geared taller than the 3rd gear in the TH125.

Let me see if I understand this correctly. If you get a 4T60 that has a 3.33 final drive you can change the chain ratio to make it a 3.73 correct? Or do you have to change the 3.33 final drive to a 3.73 and then keep the chain ratio at 1:1 ? I wanna get the most performance out of this tranny and really dont understand how all this works!

Thanks,
Jason

If you have a 4t60 with a 3.33 final, change the chain sprocket to a 33/37 and you'll have a 3.73. It should be a blast to drive. I have a 3.42 and love it

------------------

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

quote Originally posted by Blacktree: The specs I've read show the TH440 and TH125 with almost the same gear ratios in 1st through 3rd. But of course, the TH440 has a fourth gear. The trick is to find (or build) a TH440 with the lowest-geared final drive you can get (something like 3.73 with the right chain sprockets), which will improve acceleration in 1st-3rd gears. Plus, 4th will still be geared taller than the 3rd gear in the TH125.

I concur with Blacktree's observations, and they are borne out elsewhere (http://spacecoastfieros.com/tech/440-4T60/index.html).

First gear in the TH440 transmission (2.921) is only 3% numerically higher than in the stock TH125 transmission (2.840).

Conversely, second gear in the TH440 (1.568) is actually 2% NUMERICALLY LOWER than in the TH125. The difference again is trivial, but it favors the TH125.

Both transmissions have the same third gear (1.000).

The bottom line here is that the differences between those two transmissions in the first three gears essentially are (as Blacktree alluded to) either trivial (3% one way, 2% the other) or nonexistent (1.000 transmission gear for both transmissions while in third gear).

The primary difference between the transmissions is that unlike the TH125, the TH440 has a fourth, "overdrive" gear ratio (0.705) which will considerably reduce RPMs while cruising at highway speeds.

As for the off-the-line acceleration difference that "foxgapfiero" sensed, I suspect it probably was quite real, but more likely a function of the greater torque afforded by a (3.4L / 2.8L =) 21% larger engine, rather than by a (2.921 / 2.840 =) 3% numerically higher first gear transmission ratio.

In your case, BrewCheese, you state, "... this car is only a `fun' car and very rarely makes it on the expressway or over 60 mph. Keep in mind fuel economy doesn't matter in the slightest degree as I maybe only fill the car up a couple times a year."

Under those circumstances, you don't have to gear the car for even as short a distance as the quarter mile. You can gear it for pure "zero to 60."

In fact, given your situation, BrewCheese, I'd be inclined to run the silliest, numerically highest final dive ratio that I possibly could, just for the sheer FUN of it --- ESPECIALLY since, as you state, "fuel economy doesn't matter in the slightest degree."

Thanks for the help so far guys! Project34 thats why Im thinking of changing the chain ratio to a 3.73. If I change it to a 3.73 chain ratio what does that make my 1, 2, and 3rd gear ratios?

Thanks,
Jason

Yup, you use the 3.33:1 final drive with the 33/37 sprockets to get the 3.73:1 ratio. This will not change the ratios of the other gears, per se. But it will change the actual drive ratio as measured at the wheels.

Just multiply the final drive by the ratio of each gear. That will give you the actual drive ratio at the wheel. Some examples:

Let's look at a TH125 with the 3.33 final drive and 1:1 sprockets.
1st Gear = 2.840 x 3.33 = 9.46:1
2nd Gear = 1.600 x 3.33 = 5.33:1
3rd Gear = 1.000 x 3.33 = 3.33:1

Now let's look at the TH440 with 3.33 final drive and 33:37 sprockets.
1st Gear = 2.920 x 3.73 = 10.89:1
2nd Gear = 1.568 x 3.73 = 5.85:1
3rd Gear = 1.000 x 3.73 = 3.73:1
4th Gear = 0.705 x 3.73 = 2.63:1

As you can see, the "high performance" TH440 will get you more torque @ the wheels in 1st through 3rd, plus higher top speed in 4th gear. Compared to the TH125, it's a win/win situation.

I think I just talked myself into a TH440 swap.

[This message has been edited by Blacktree (edited 04-14-2007).]

I have a 4T60e mounted to my 4.9 and I'm ready to dump it for a 5 speed manual. The auto is no fun at all to me, I would rather shift and get the better acceleration off the line as well as the overdrive gear.

quote Originally posted by BrewCheese: Thanks for the help so far guys! Project34 thats why Im thinking of changing the chain ratio to a 3.73. If I change it to a 3.73 chain ratio what does that make my 1, 2, and 3rd gear ratios?

In regard to that question, Blacktree's tables above do an excellent job of illustrating the differences between the TH125 with the stock chain versus the TH440 with the 33/37 chain sprockets.

Keep in mind, however, that acceleration (in each of the first three gears) using the TH125 with 33/37 chain sprockets would be much the same as acceleration with a TH440 using those same 33/37 chain sprockets. Therefore, BrewCheese, if you REALLY mean it when you say "fuel economy doesn't matter in the slightest degree," there is no particular acceleration advantage to be had by using a rebuilt TH440 rather than a rebuilt TH125.

In fact, for you, BrewCheese, a potential DISADVANTAGE of such a transmission swap is that if you do plan to use the overdrive afforded by the TH440, you then will need to go through more work with the TH440 swap to be able to access its first gear on your transmission console.

Right now, for example, your "transmission selector lever" currently has only these options available for the TH125, each visible on your console: "P,R,N,D,2,1." With only those options currently available, AND access to the TH440's overdrive, you will need to do more work to be able to access first gear with a TH440, because it has four forward gear selections, versus the TH125's three.

Please re-examine the tables provided by Blacktree. In terms of pure off-the-line acceleration, it's apparent that a TH125 with access to first gear will blow the doors off a TH440 without access to first gear --- even if the TH440 employs 33/37 chain sprockets. Under those circumstances, the relevant multipliers from Blacktree's tables are 9.46:1 for the TH125 (in first) versus only 5.85 for the TH440 (in second). That is a HUGE (9.46/5.85 = 62%) difference!

I'm not knocking the TH440 swap. Like Blacktree, I myself may do one. I'm merely pointing out that for your purposes, BrewCheese, maybe you don't need one, and you can simply use a rebuilt TH125 instead --- ESPECIALLY if you're quite serious when you say, "fuel economy doesn't matter in the slightest degree."

Umm... the TH440 will start off in first gear anyway. Think about it.

However, Project34 has a point. If your only concern is off-the-line acceleration, then you might be better off putting the 33:37 sprockets in your TH125. It doesn't require any mods to fit, and doesn't add any extra weight to the car (the TH440 is heavier).

Can you put the 410 final drive from the 4-speed in the automatic? If so that would be *bad* (& exactly what the OP is looking for).
BTW, any of you know what gearing is in a '91 Lumina 4T60E? I'm putting one behind a 283.
Thanks,
~ Paul
aka "Tha Driver"

Scientists say we only use 20% of our brains. But if they're only using 20%, how would they know?

quote Originally posted by Blacktree: Umm... the TH440 will start off in first gear anyway. Think about it. However, Project34 has a point. If your only concern is off-the-line acceleration, then you might be better off putting the 33:37 sprockets in your TH125. It doesn't require any mods to fit, and doesn't add any extra weight to the car (the TH440 is heavier).

To avoid the potential for misunderstanding, perhaps I should have been more precise in my choice of terminology. Suppose I want more than what I termed "access" to first gear after making the TH440 transmission swap. Suppose that I (as opposed to GM) want to be the one who decides, after putting the trans in first gear, when it should come OUT of first gear.

Currently, I can do that with my unmodified, stock TH125, when, with this three-speed automatic transmission, I accelerate from a standing start after placing the "gear selector lever" in "1."

Without additional work, how do I do that same thing --- AND retain overdrive --- in a Fiero sporting a TH440, a FOUR-speed automatic transmission? That requires additional work to my console to do that, does it not? As you know, the stock Fiero console currently provides only the choices, "P,R,N,D,2,1."

Thanks for all the help and tables and stuff! :) One of my big things for going with the 4 speed is that I picked up a 4 speed really cheep and can do the rebuild and everything on the ground, mount it on the spare cradle and just be able to swap it out with minimal downtime. Also Im worried it I put the 3.73 chain in the Th125 and am cruising at 50-60 mph how high are my RPM's going to be. THere already getting up there with a 1:1 chain in the stock 3.33 TH125. Where as the TH440 I will be in overdrive with a 2.63:1 ratio and still using a 3.73 chain, a lot lower then the stock 3.33 in the Th125 with a 1:1 chain.

I do very rarley make it on the expressway but If I do end up taking it on the expressway with a TH125 and a 3.73 chain the engine is going to be absolutly screaming at 80 mph. For the little bit of work of swapping in the TH440 it only makes sence to me to not limit myself to a 90 mph (complete guess) top speed. (right??) I couldnt even run it down the drag strip in fear I would redline the engine, not to mention the 2.8/3.4's dont really like high rpms.

As for manually shifting...most of the time it seems to take more time to manually shift a auto verses letting it do it itself. Some of the standered auto shift lag can be taken care of by using a shift kit to.

Jason

If you look at your automatic shifter it does have 7 notches. You use only 6 of them with a 125. With my 4t60 I us all 7. It will go into 1st and stay there until I shift it. I also feel the 4t60 is stronger than the 125 and shifts better too. Us the 3.73 final in a 4t60, you won't be sorry. I picked the 3.42 final so I could stay in 3rd threw the 1/4 , top speed 117 with an ET of around 12 sec. Still working on the tuning and have to add direct port nitrous ,125hp. Also with my old 125 I could run a flat 15 sec and stay in 2nd when I went threw the traps.

------------------

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

Ive heard some people say there shifter has 7 notches and others say only 6 and they had to make a 7th. I guess I will pull my shifter trim piece and take a look. Maybe the later years had 7 notches?? Lilchief is that 14.9 with the 3.4 or 2.8? Any mods on the 3.4?

Thanks,
Jason

quote Originally posted by BrewCheese: Ive heard some people say there shifter has 7 notches and others say only 6 and they had to make a 7th.

I'm beginning to think the contributors to this thread may be talking about two different things.

The TH-125 is the transmission that came with all STOCK automatic-transmission-equipped Fieros.

In STOCK form, the Fiero's shifter console on my `86 GT has 6 notches, not 7. They are labeled, quite simply: "P,R,N,D,2,1." They are not labeled, in STOCK form, "P,R,N,D,*3,* 2,1."

Perhaps we've been talking about two different things? Are we, for example, discussing a MODIFIED Fiero center console that offers the 7 selections, "P,R,N,D,3,2,1" rather than the STOCK Fiero center console, that offers only the 6 selections, "P,R,N,D,2,1"?

quote Originally posted by project34: In STOCK form, the Fiero's shifter console on my `86 GT has 6 notches, not 7. They are labeled, quite simply: "P,R,N,D,2,1." They are not labeled, in STOCK form, "P,R,N,D,*3,* 2,1."

The actual shifter has 7 notches, only 6 are used and therefore only 6 are labled.

quote project34 said: Perhaps we've been talking about two different things?

I believe the other guys are talking about the notches in the shifter mechanism, not the "PRNDL" display. If you remove the shifter surround and look at the base of the shifter, you'll see that it has several notches in it. These are what keep the shifter lever from flopping around. And sure enough, there's one unused notch behind the 1st gear notch. So with a 4-speed auto, that extra notch might be usable for 1st gear.

So how hard is it to actually mount this trans?

BrewCheese, The 14.9 was with a highly modded n/a. 3.4. I should be in the low 14's or high 13's with new transmission and new chip

------------------

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

quote Originally posted by Jncomutt: So how hard is it to actually mount this trans?

Its not. Rockcrawl has the info you need on his website. I've done 2 TBI caddy swaps with the 4t60 (non-e) and the info from Jon was pretty much dead-on.

quote Originally posted by Cooter: Rockcrawl has the info you need on his website.

Although presumably helpful, that information seems a tad unnecessarily cryptic.

Google currently shows 9,280 entries under "Rockcrawl." What specifically is the address of the website you believe we need for this transmission swap?

Heres Rockcrawls website:

http://www.fieroaddiction.com/4T60a.html

Everyone tells me rockcrawls the expert and the info on this website is the most accurate around.

Jason

Thanks for the link, I looked at the site and couldn't find it. He should put a link on his homepage.

So basically it needs a modified cable bracket, vacume line to the trans, and P6000 axles? Seems pretty straight forward.

[This message has been edited by Jncomutt (edited 04-16-2007).]

Its not like a "highly skilled" swap. I think If you can swap out a stock tranny this really wont be any harder.

Jason

quote Originally posted by BrewCheese: Its not like a "highly skilled" swap. I think If you can swap out a stock tranny this really wont be any harder.

I think I can manage that..

Me to....hopefully. Does anyone know where I can get the 3.73 chain now?? I know someone posted a website for it at one time but cant seem to find it now.

Thanks,
Jason

Bump cuz I want a 4t60.

Wouldn't the chain be the same? I mean 33/37 or 35/35 or 37/33 all equal 70 teeth. Anyone?

Yes, they all equal 70 ,even the odd ball 38/32. Chain/gear sets are different in the 125 and 4t60. Plus 4t60 is stronger and shifts better.

------------------

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

ok ive been wanting to do this swap for a long time but cant find the tranny in any of the Salvage yards near me. I run into alot of the 4t60e transmissions and i was wondering since i plan on doing the 7730 ecem swap with DIS anyways what else would be nessecary to complete it with the electronic transmission?
Edit: Alos would the chain swaps and everything else be the same for the Electronic Transmission?

[This message has been edited by Lancealpha (edited 09-21-2008).]

With only a pushrod 3.4, even using stock 2.8 manifolding and the stock Camaro 3.4 cam,you'll still not run out of rpm in a 1.4 mile with 3.73:1 gearing, assuming reasonable tires. Like a pair of 235/60R15 drag radials, which fit fine and look great! Using 4 gears in the 1/4 really wouldn't be an advantage, and you'll lose a tenth to that 3-4 shift. No, you can't put the 4.10:1 final from the Muncie in your automatic. To get the car to feel more like it has 4.10 gearing, first go to a 215/60R14 drag radial, and second, figure out a way to do a 32 and 38 tooth setup with the 32 tooth driving and the 38 tooth being driven. Or do I have that backwards?
Anyway, if you do run out of rpm, start with the Crane 272 cam.