Okay, I just did the swap, and having gotten a bad tranny (Pick and pull) I had to do it a second time. So I learned quite a bit about this swap and put together a bunch of notes. A lot of this is just stuff consolidated from other sites:

Which if you have a Fiero and you're not reading, you should be. Tons of stuff here, especially in the archives.

Now the information on this page is not in any particular order. I made the page for my own needs as a place to keep information. However there is A LOT of stuff here not covered on the three pages above that I either learned on my own or from a thread/discussion on the forum. All of the charts here however are pretty much taken directly from the first three pages above. I really should go do individual attributions for them. A lot of the notes around the charts came with them. Read those sites, and you'll see how owns what. And really do read those sites! The more information you have, the better! And there may be things there I didn't put here, that are important to you, but weren't to me. (plus I know there is stuff there that is important that I didn't put here, so there!)

Also, further down on this page I will put information on basically how I did the swap. There won't be any pictures (I was too busy getting the job done, sorry!) but I will put the order I do things in, and how, as best as I remember it. 

There are several combinations of axle used in 6000 so it's easy to get the wrong ones. By comparing notes from a number of articles/threads on axles and measuring the Fiero axle threads, I found the following in the CV Unlimited catalog. (You can download an Excel version of it from their site.) (this came from Ogre I think)

Notice that both the 6000, and the Ciera in the Space Coast article are listed. This should help you isolate the correct used parts as well as new ones if needed.

The most obvious determining factor between the various AOD axles for the cars above seems to be the diameter of the threaded portion of the outer CV. A spare Fiero axle nut is a good tool for checking that. It was the nut size specification that I used to figure out the data above... 0.785 inch is roughly 20mm. The "Wrong" ones have are larger (23-24mm) and won't fit the Fiero nut or hub opening

There are 3 variations of speedometer assemblies that I have seen on 4T60 transmissions. One type is almost exactly the same as the one used on the TH125C transmission and will plug directly into the Fiero speedometer connector. A 2^nd type is almost the same as the first except the speed sensor (item 1) has been replaced with an assembly that screws into a mechanical speedometer cable. This type can be used if reassembled with speedometer sensor from your old transmission. Both the mechanical cable and sensor type speedometer assemblies are held in place by a 1-inch wire clip on the top of the governor cover. NOTE: The TH125C governor cover (item 3) is NOT interchangeable with the 4T60. (Note: This is incorrect from my experience, and that of Rockcrawls)

The 'Final Gear Ratio' is merely the product of all gear ratios involved. Thus, in our example it is 5.885 (1.708 * .973 * 1.25 * 2.833). We can now use the formula:

Here are all the possible ratios and the RPO codes for ones GM actually built. These RPO codes are additional to the Transaxle Type RPO. This means that on a vehicle's build sticker you'll find MD9 for TH125c (3T40) or ME9 for 440-T4 (4T60) and one of the codes below to tell you how the transmission is geared. (Assuming you still have the original transmission...) The last column reflects a couple spots where GM and MS Excel rounded the number differently.

I forget who posted this:

You may also have missed out on the opportunity to install a higher stall converter. It makes a big difference going from what was probably 1800 stall to 2300. My 3.4L had a 2385 stall converter (~$65) on a 4 speed automatic with 3.33 final drive and from a stand still it would smoke the tires if you floored it.

FZ -- 2390 stall behind a 4 cyl
FY -- 2060 stall behind a 6 cyl
FJ -- 2060 stall behind a 4 cyl
FD -- 2090 stall behind a 6 cyl
FG -- less than 1800 stall behing a 6 cyl

Note: The TCC went from a 4 wire plug to a 5 wire plug in 1990. I have also heard from recyclers that the 87 tranny isn't that hot. (My bad one was an 87).

Note: The pontiac 6000 motor mounts work well, and the axles from a pontiac 6000, 1987, Light duty brakes, no ABS fit perfectly.

Note: This tranny takes AT LEAST 12 quarts of fluid, more like 14. (I think 6 of that goes in the TC)

Note: Get the metal tranny cooling lines with the tranny. Your TH125 ones won't work right as they're the wrong length and not bent.

Note: If you have a 3.4L engine, you may have to grind some more off the block by where the one bolt connects the tranny and engine from the opposite side of the others. The 4T60 is larger, and needs more removed than the TH125.

Note: The tranny line support bracket by the motor mount was a pain in the butt for me. I suggest not using it.

Note: You can swap governors from the TH125 in many cases. May make it shift better. May not. Up to you to experiment if you want to.

Note: On the 5 pin TCC switch:

A. RED +12V from brake switch. This is PURPLE on the FIERO (pin A on the trans).
B. WHITE 4th gear switch (you won't use this).
C. GRN 3rd gear switch (you won't use this).
D. BLK To the ECM TCC control. This is BLK/TAN on the FIERO (pin D on the trans).
E. BLUE Temp sender (you won't use this). (Also, this isn't always a temp sensor, depends on year)

The pins on the trans aren't in order (that would have made sense...).

TOP

E
B C
A D

Bottom

Again,there are a couple of different wiring pinouts so you need to check for the red and black wires for the TCC.

(Thanks to Terry, TK on the forum)

Note: Most fiero shifters will still let you shift to 1^st, though it will be off the indicator. At least mine does.

Okay, I'm not the fastest mechanic in the west, but I can pull the tranny by myself in about 4 hours, and put it back in, in about the same time (this includes taking it off the cradle). One thing I recommend is that you buy A motorcycle jack/lift. They cost about 100 dollars at costco, and have two large rubber covered arms that stay level as they go up and down. Mine handles 1500 lbs. More than enough to hold the cradle. I also leave the engine in the car when I pull the trans, cause it's easier.

Anyway, this is how I do it. Note that all the standard disclaimers apply: I take no responsibility for anything that happens to you if you follow this, and this list may be incomplete, I expect you to look at it carefully and think long and hard. Any screwups are your fault and responsibility, not mine. Also some things can be done in different order.

Please Note: YOU MUST have an 18mm open end/box wrench, an 18mm deep and 18mm shallow socket. Or you'll never get this done. You also need the same in 13mm and 15mm. Any type of 10mm will deal with the small ones. I forget the size of the axle nut, but it is big and you'll need a breaker bar. Refer to your manuals for torque settings!

Reinstalling is pretty muck just doing everything in reverse. Get the tranny and cradle nicely balanced on that lift and roll it under the car. Once you have the cradle secure and have started to lift the engine and tranny into place (by secure I mean the bolts are in the cradle and the engine is starting to rise as you lift the cradle and it's pretty much even with the tranny but just won't seem to line up perfectly and pull together) you can disconnect the dogbone. A good shake or two and it will probably mate right up. Also, a jack under the oil pan, close to the tranny (after the cradle is bolted in) will help the tranny and engine to slide together now, because they're sagging at this point. This is just more 'finesse'.

Remember to watch those two bolts for the engine mount on the passengers side, some coercion with a large bar may be needed to line them up. Also keep an eye on the shock towers and as soon as they are lined up and in put some bolts on them. You don't want it all falling out now, do you?

And DON'T forget to bolt the flywheel to the Torque converter! And don't tighten down the first bolt until all three have been put in. And make sure that the torque converter really is seated all the way down on that spline!

If you are putting in the 4T60 something's to remember:

1. Remove the Vacuum modulator, it won't clear the water pipe.
2. You'll have to make some kind of custom tranny/engine bracket (That's the one that goes between the tail end of the tranny and the engine)
3. You will have to use some finesse (ie a large metal bar) applied carefully to move the tranny around a little.
4. Make sure that the Vacuum modulator really is bolted down (pull on it!) otherwise it will pop out the first time you step on the gas hard and make quite a mess.

Again, Disclaimer: I am not a professional mechanic, and this information is offered for suggestion only. I take no responsibility at all. If you hurt yourself, or damage your car, don’t come to me.

I do hope this helps. This is not the best way to do it, I'm sure there are much better ones. This is just the way I've done it, and it has worked for me. Good luck.