Warning! Don’t force anything into the ALDL connector! If you damage the connector then you can have problems when using ECM scanners and other tools that have the proper size terminals.

Note! It is possible that the ALDL may be installed with the Key up or down.
The above picture is Key Down. Use the key sticking off the ALDL by terminals C & D to determine which way the ALDL is positioned.
With the key down, when you are sitting in the drivers seat, Terminal A is on the bottom row on the passenger’s side. With the key up A is the top terminal closest you.
To read ECM codes short terminals A & B together and turn the key to run, codes will blink thru the Service Engine Soon light. (Don’t start the car!)
Terminal F is used for some tests of the Torque Converter Lockup System. See the TH125 article for more information.
Terminal G is the fuel pump test point. It will have 12V on it whenever the pump is on. It can also be used to feed 12V to the pump to determine if the pump or the controls are a problem.
None of the other terminals are used during normal service routines so leave them alone. If you short them out you could do major damage to the ECM. (Only a few terminals in the ALDL are even wired.)
You can find the complete pin out of this connector and others here –> Fiero Tech Zone He also has a brief ECM code list.
There is a cheap tool to read codes in the tool section of most parts stores. It is a simple stamped metal item and cost about $2. You can also use any wire that will make snug contact.
If you have an Autozone store near you ask the counter man for the book and key to read the codes. The book is titled “What Does It Mean When Your `Check Engine’ Light Comes On?” This small book lists common codes for GM Ford and Chrysler and how to test some of the ECM sensors. The book is free.
The best tool for dealing with the ECM is a scanner. These tools read the full data stream from the ECM and will report data from sensors and how the ECM is reacting to it. The AutoXray GM OBD-1 scanner is one of many tools available and cost about $150-200. Other scanners are available but most cost more.

4 Speed Automatic for your Fiero – 440-T4/4T60/4T60E

The Turbo Hydra-Matic 440T4, later renamed Hydra-Matic 4T60, and the Hydra-Matic 4T60E are a popular swap for the Fiero. This is partly due to the fact that they are original equipment with many of the popular engine swap choices. They provide an additional gear (overdrive) and increased power handling with only a minor weight increase over the Fiero’s Hydra-Matic 125C. They are almost a direct drop in, requiring only a few small modifications to existing parts.

The 440T4 or 4T60 is the first generation of transversly oriented 4 speed automatic transaxle. It was used in GM mid and full size vehicles until about 1990. It only requires manifold vacuum to the modulator valve and throttle input via the throttle valve cable to  operate. Both are adjustable for shift quality. Torque converter lockup is controlled by  the ECM, or aftermarket kits are available for vehicles without a computer. The 4T60 was replaced by the 4T60E. The 4T60E is shifted electronicly using solenoids controlled  by the ECM. It still has a vacuum modulator, but the TV cable is eliminated. It will not  operate without computer control, therefore it can only be used with an engine that was originally equipped with a 4T60E.

There are several different overall drive ratios available in these transmissions ranging from 2.73:1 to 3.73:1, and possibly more. The overall ratio is a combination of the drive  & driven sprocket ratio and the final drive ratio, and has nothing to do with 1-4 gears.  The sprockets and chain are located behind the side cover and are available in 33/37,  35/35, and 37/33 combinations. The drive sprocket takes the engines rotation and  transfers it through the chain to the driven sprocket and 1-4 gear sets. At the end of the  1-4 gear sets, on the tail end (passenger side) of the transaxle, is the final drive  planetary gearset and differential. The final drive gears can be changed on a 4T60E by  removing four bolts and a snap ring. To change final drive gearing on a 4T60 you need  to entirely disassemble the transaxle.

Mounting the trans in a Fiero is quite simple. The correct brackets can be found on almost any 4T60, and most early 4T60E. They look very similar to the Fiero 125 brackets, but are made to fit the mounting points on the 4T60/E case. There are holes in the brackets that line up with bumps on the rubber mounts to prevent them from twisting when the nut is tightened. The hole in the rear bracket must be re-drilled on the opposite side of the bolt hole so it matches the Fiero rubber mount. Rubber mounts for any year  or model Fiero will work, excluding ‘87 and ‘88 4cyl autos.

The slotted holes in the cradle for the rear mount need to be moved toward the center 1-3/8″ for the correct positioning of the trans.

There is not enough room on the ‘88 cradle to allow drilling new holes in the correct location. My solution is to cut and section a portion of the cradle as shown in these before and after pictures. The third picture in this group also shows where the rear part of the cradle may need to be trimmed for pan clearance (‘88 only).

The shift lever needs to be flipped 180* to match the reverse pattern of the Fiero shifter. The lever needs to be flat to allow clearance for the exhaust crossover pipe in most cases. It also needs to be shortened to get the correct ratio for the Fiero shifter. It should be 1-5/8″ from the center of the stud to the center of the hole. The cable mounting bracket is fabricated using pieces of the 4T60 and TH125C brackets. The part of the TH125 bracket where the cable attaches is cut off and welded to a piece of the 4T60 bracket.

With a 3800 engine, the plastic cable end comes extremely close to the exhaust crossover pipe. For those swaps I break off the plastic end and weld on a stainless steel 1/4″ female rod end. The plastic end has not been a problem with the 4.9 swaps. Below you can see the adjustable cable and the steel rod end installed.

The stock Fiero axles cannot be used with the four speed automatic. For a 4T60 you can use right and left axle assemblies for a ‘89 Pontiac 6000 with 4T60 and light duty brakes. The correct part numbers are A1 Cardone P/Ns are 60-1115 and 60-1078 or CCT 8471 left and 8430 right.

For a 4T60E you can use the same left axle for a ‘89 Pontiac 6000 with 4T60 and light duty brakes on the left side, and a left axle for a manual Fiero on the right side. Some people have reported having problems with the Fiero axle on the right side, but they have always worked well for me. There are plenty of other combinations of parts that can be used to assemble axles that will fit, but those are the simplest solutions. They can be purchased off the shelf at most auto parts stores for about $60 each and install without modification.

Torque Converter Lockup.

Why is TC locking important?

The biggest reasons are fuel economy and heat control. The TC is the car’s single biggest heat generating device besides the engine. The transmission will run significantly hotter if the TC doesn’t lock. Before listening to people that tell you it doesn’t matter read this article from Borg Warner. Borg Warner Tech Tips, Transmission Fluid. It will also increase heat load on the radiator since it also cools the transmission. That could lead to easier overheating if the cooling system isn’t 100%. With the TC locked there is almost no heat from the transmission.

You’ll also waste gas. Likely allot. One of the advantages of having a locking torque converter is that it allows the TC to be built with more “slip” which increases the torque multiplier effect. This increased multiplication translates into quicker launches but horrible fuel consumption. Once the transmission reaches top gear, the TC is locked eliminating the slip that is now just wasting fuel and making heat. This is why today’s automatic transmissions both perform better and get nearly the same fuel economy as a manual transmission would. To learn more about the locking TC, go hear–> Motor Magazine Back Issues, and select the May 1999 issue then go to the bottom of the next page that opens. If you have acrobat loaded just get this–> Motor Magazine Torque Converter Article PDF.

Testing

TH125c has a locking torque converter system controlled by 4 electrical items. They are listed in the order of their location in the circuit. (Starting at the fuse end)

1. The Brake Pedal Switch. This switch opens to unlock the TC when you press the brake. It is on the brake pedal hardware.
2. The Third Gear Switch. This is inside the transmission. It closes only when the transmission is in third gear.
3. The Converter Lockup Solenoid. The device operates a valve that pressurizes a clutch and locks the converter.
4. The ECM. The ECM switch closes a connection to ground only when the car is doing a fairly constant speed above 35mph.

There are 2 tests for problems with the Torque Converter lockup system. These tests should BOTH be done before any shift problems are looked at. The first, and easy, test for TC lock is to press the brake while doing a constant speed over 35mph. (The test WILL NOT work if you are accelerating or slowing.) You only need press the pedal enough to activate a switch. (About 1/2″ ­ 3/4″) If the TC is working right you should see the tachometer jump up about 200RPM then drop again when you let off the brake.

The second TC test is to pull the TC lock’s electrical connector. It’s on the front of the transmission. Unplug it and see if you still have problems. The second test is very important if you are stalling when stopping the car or if the car bucks badly when slowing. There are known issues with the Torque Converter Lockup Control Solenoid. This device can hang the Torque Converter Clutch in the locked mode, usually when the transmission is hot.

If the second test stops the problems then the TC control solenoid likely needs to be replaced. This repair can be done with basic tools. It’s not hard just very time consuming. The Solenoid is under the side cover of the transmission. While replacing the solenoid it’s a good idea to replace the Third Gear Switch, which is next to it. Then you’ll have all new electrical parts in there. If you don’t see the RPM jump while doing the first test you may have a TCC apply problem. This could be electrical, TCC solenoid, TC clutch or hydraulic problems.

The test for the brake switch is in the Manual lockup section at the end of this page. The test for the Third gear switch is a bit different. If you watch ALDL terminal F with a voltmeter you’ll see it go to 12V when the TG switch closes but then you’ll see it drop again when the switch in the ECM closes. At this point you’ll be able to watch the ECM lock/unlock the TC depending on driving conditions. This only tells you that the electrical system is OK. You could still have a hung TC solenoid or other problems in the transmission.

Once the electrical problems are ruled out then it’s either solenoid hydraulic or the torque converter itself. Hydraulic or TC problems are beyond most people but if you do work on this yourself the best source of information on this is a GM document that covers the whole TC lockup system step by step. A very good general guide on this was provided to trainees at a GM seminar and is not part of the shop book. It is however on ALLdata. You may be able to get this from a friendly shop. I think ALLdataDIY.com may also have it.

Reading the TC ID Label There are different Torque Converters used with the various engine and transmission combinations. The V6 TC may not perform properly on an L4 and vise versa. I don’t think the 3T40 torque converters will work in the 4T60. (I don’t have any way to check.)

The ID label may still be on many converters, here’s how to read it. (The following TSB has been reduced to cover only 245mm units. The larger 298 mm units are used with inline transmissions.)

Torque Converter Identification
TRANSMISSION: GM All
BULLETIN: # 010 REVISED
SUBJECT: Torque Converters
DATE: September 1990
GM Torque Converter I.D.

The 245 mm dia torque converter I.D. code works the same way as the 298 mm converters, but with different meanings.

The first digit of a 245 mm converter refers to the application.

F = Front wheel drive
H = Rear wheel drive (except THM 180’s)
S = THM 180

The second digit is the “K” factor. The chart shows the “K” factor for each code along with the stall speed. Note: Multiply the “K” factor by 11.6438 to get the stall speed of a 245 mm torque converter.

CODE   K FACTOR       STALL SPEED
A      240            2795
B      220            2560
C      205            2385
D      180            2095
E      160            1860
F      148            1720
G      140            1630
H      130            1514
J      177            2061
K      237            2760
L      163            1897
M      131            1525
N      218            2538
Y      122            1420
Z      203            2363

The third digit refers to the clutch type.

CODE DAMPER TYPE
0    No converter clutch
1    12O ft/lb
2    104 ft/lb
3    170 ft/lb
4    215 ft/lb Heavy Duty
5    215 ft/lb *RTC
6    170 ft/lb Heavy Duty
7    215 ft/lb *RTC Heavy Duty
8    Viscous Clutch
9    240 ft/lb
A    215 ft/lb
B    215 ft/lb *RTC

* RTC = Reverse Torque Control (poppet valve)

The fourth digit (optional) refers to the type of cover used.

CODE COVER TYPE (APPLICATION)
A    FWD 208.2 mm Bolt Circle
B    FWD 237.0 mm Bolt Circle
C    FWD 237.0 mm Bolt Circle (viscous Clutch)
D    RWD 247.65 mm Bolt Circle
E    RWD 237.0 mm Bolt Circle, No Converter Clutch *
F    RWD 237.0 mm Bolt Circle *
G    RWD 247.65 mm Bolt Circle *
H    RWD 247.65 mm Bolt Circle, No Converter Clutch *
K    RWD 237.0 mm Bolt Circle, No Converter Clutch *
P    THM 180 ISUZU
R    THM 180 Opel
S    THM 180 BMW

* 180 degree weld on each lug

Look at the code on the torque converter in figure 6. You can easily identify it as a front wheel drive model. (The first code is an “F”). The stall speed is 2760 (the second code is a “K”), and it has a damper assembly rated at 120 ft/lb’s (the third code is a “1″.) Notice that the fourth code has been omitted.

Manual TC lockup.

Warning! Manual TC locking presents a number of problems and can damage the transmission. It is potentially dangerous to drive with a manual lock active. Manual locking should ONLY be considered when the ECM has been removed such as when a carbureted engine has been installed.

Notice! This is an EXPERT level article and it assumes the ECM was unplugged and that the wiring is intact. If the harness has been cut it is up to you to return it to operating condition. This topic is only covered as an aid to installation of non-stock engines.

Manual locking of the TC WILL NOT help performance. Manual locking is used only help gas mileage on cars without an ECM. Even then it is preferred to find an automatic solution to the problem. On cars with an operational ECM, delaying the locking of the TC can help performance. This company can tell you more about that-> Transmission Exchange Co.

Before you can install a manual lock. You need to test the brake and third gear switches. BOTH switches Must work. Without both switches you cannot wire the manual switch without damaging the transmisson.

There are 2 wires on the TC lockup connector. The first wire, according to GM schematics, comes from a switch on the brake pedal. The other wire coming from the transmission connector is ground. The ECM used to ground that wire to activate the TCC. Your new switch will replace the ECM.

The brake switch. Disconnect the transmission plug and hook a test light to the wire that is always hot with the key on and hit the brake pedal. The line should go dead. If it doesn’t you can’t wire the switch manually. The Brake Switch MUST work or you’ll have nothing but problems. Dangerous problems.

The third gear switch. This switch must also work or the TCC may try to activate as soon as you take your foot off the brake when stopped. This is not a good thing. (Same effect as dumping a clutch every time you take your foot off the brake. You WILL brake the tranny like that.)

To test the third gear switch connect a voltmeter between the TC ground wire and body ground. TCC ground is Terminal F on the ALDL. Put the meter where it can be seen while driving and have a passenger watch it. When the car goes into third the meter should swing up.

Warning! You MUST use a voltmeter for this test! Test lights may pass enough current to allow TC locking. This is not a good thing just now. This wire should only be hot when the transmission is in third gear. If you see a voltage on the line when stopped then the third gear switch is bad.

The manual lock switch is connected between the transmission ground wire and the vehicle ground. When the switch is closed the Torque Converter will lock anytime the transmission is in third gear.

Manual locking presents several problems!

You want to avoid using the manual lock except for highway driving. You don’t want the tranny locking as soon as it hits third gear, which is exactly what it will do with the switch on. If the TC locks at the same time you hit third you’ll likely tear up the tranny. (You also lose some performance that way.)

If you get into heavy traffic you’ll want to leave it unlocked, even if the tranny stays in third.

The most obvious method to do this is a simple toggle switch. Problem is a toggle switch doesn’t allow for the driver forgetting it’s on. If the toggle is on then the transmission will lock as soon as it hits third gear, which isn’t what we want for either reliability or performance.

The preferred way to restore TC locking is to make a speed sensor for the circuit. That way the TC will never lock below a specific speed. The ECM cutoff was no lock below 35. In most cases setting the cutoff for no lock below 35-45, and add Transmission Exchange Co.’s TCC delay unit, would return auto locking in the safest way possible. Ideally the speed sensor should only lock at relatively constant speed. It should unlock when speed changes rapidly.

A second option is to make a control with a push button. When the button is pressed the TC locks but when the brake is pressed or the transmission goes out of third gear the circuit resets and leaves the TC unlocked. This gives the same result as a simple toggle switch on the highway without some of the safety and drivability problems. (This circuit is Very easy to do and really cheap.)

Either control circuit would be fairly easy to do. There’s a 2000ppm feed back to the ECM connector from the dash. There’s any number of ways to make that feed close a switch at a particular speed or above.

There are a bunch of things about the TH125c transmission that need to be kept in mind when working on it. This is a collection of the issues asked about in the forum. It’s by no means a complete list of things. It does however cover some obscure things needed by customizers.

Shift Problems

Do the Torque Converter tests in the TC article. What feels like a shift in TH125 could really be the TC locking or unlocking. If there is a problem with the TC lock then it can feel like you’ve lost a gear. Does the problem happen with the TC lock plug disconnected? (If the TC lockup is working correctly you usually don’t notice it at all but do the test anyway.) When does the problem happen? If it is only one shift/gear then you very likely need a shop to work on it. You can try the stuff below but don’t be surprised if nothing helps. If the problem is with all gears, it could be something dumb or major. Check the easy stuff before panicking. First of all make sure that the transmission fluid is at the right level. Over or under fill will both cause shift problems. What condition is the fluid in? If it’s turned light or even clear then it’s old, likely oxidized, and you might want to try changing the fluid and filter before taking it for repairs. If it’s brown to black or smells different from new fluid then the transmission may have fried a clutch. You could try changing fluid but you should probably take it to a shop to be checked out.

The next item to check is the Throttle Valve Cable, which runs from the throttle linkage on the engine to the top of the transmission. If this cable is binding or out of adjustment you will have shift problems. Another thing that happens is the Governor or a passage inside the valve body gets blocked with a flake of dirt or sludge. This can affect one shift or the whole transmission. You can try one of the cleaning products that you add to the fluid. Some people have reported good luck with these. Depends on just what’s blocking the passage if it will work or not. If this fixes your problem then do a fluid and filter change to get the rest of the dirt out. Another possibility, although rare, is that the filter has failed or come unsealed inside the tranny. The result is that the fluid is picked up higher in the transmission. This can have the same result as low fluid.

Notes

Shift Kits: These kits WILL NOT fix a transmission with problems. Worse they could hide some problems. Be sure that your transmission is good before adding the kit.

Source of parts and manuals besides GM dealer: Transmission Exchange Co. They have loose parts, full rebuild kits, Trans-Go shift kits, TC lock delay modules and various other things. The red dye in the fluid will fade over time. It doesn’t automatically mean the fluid is bad, just old.

Throttle Valve Cable
What does the TV cable do?

The purpose of the TV cable is to tell the transmission what the actual throttle setting is at any given time. TH125c doesn’t use a modulator valve so this is the only way it can get some clue about engine load. This cable IS NOT a “kick down” cable/linkage like many people are familiar with. It works with an internal governor to control all transmission shift points. The TV cable is always synchronized to the throttle butterfly and NEVER the gas pedal position. The transmission doesn’t give a rat’s ass about the gas pedal. If it is adjusted properly, the car will shift correctly even with a severely stretched cable/linkage between the motor and pedal.

You’d think the gas pedal movement would always equal the same action at the throttle but this isn’t always true. Wear and cable stretch often mean the gas pedal movement doesn’t match the movement of the throttle butterfly. This is especially the case with the 7-8 foot long accelerator cables used in Fiero.

Adjustment

WARNING!!! DO NOT EVER step on the gas pedal to do this!!!!!

Not on Fiero or any other car.

It takes considerable effort to make the TV cable adjuster move. Do Not press the accelerator pedal to make the adjustment or you’ll likely damage the throttle cable or other parts in the system, especially in Fiero with it’s snake of a cable…. You could even snap the cable. If you try to do the TV cable adjustment by mashing the pedal it will not be right most of the time. The adjustment procedure for the TV cable is in the Haynes book and is correct for all years. Note however that the location of the adjuster moved on the DIS (87-88) 4 cylinder setups. It is now on the transmission end of the cable. Also, You turn the black pulley the cables are connected to and not the throttle wheel on the TB/TBI.

Once you make sure the TV adjuster isn’t stuck etc… Pull the slide part of the adjuster about 1/4-3/8 of an inch. Be careful how far out you pull the adjuster slide. The adjustment button is normally slightly below the edge of the shell.

The button MUST NOT be crooked or pop up higher than the shell. If it does then the slide has been pulled out too far. If you try to adjust the cable with the button messed up you’ll break something.

For 87 and later L4… Rotate the idler pulley by hand until the TBI unit reaches WOT. There is a mechanical stop on the 700 TBI at WOT. This is much easier if

you hold the TBI quarter pulley against the WOT stop then turn the idler pulley until the slack is gone from the small bit of cable between the two pulleys.

As you rotate the idler, the TV cable will ratchet into the tranny. Wherever it stops you are done. (Mine ended up with the fat sliding part about even with the adjuster hole.)

Once the cable has been adjusted, it is possible you may still need to fine-tune it a little by hand. You should not need to adjust the cable more than a couple teeth. If the transmission will not shift correctly after TV adjustment either you did it wrong or there are internal problems.

87+ L4 note:

The idler pulley is bloody hard to turn by hand to make the TV cable adjustment. If you look at the idler pulley you’ll see three holes in it. You can make a tool to fit two of the holes or you can go to a bicycle shop and see about getting a special wrench, shown left, that is used for working on the gear packs of 10 speed and mountain bikes. The ends of the bike tool fit the idler perfectly.

4T60 (440-T4) Note

Warning! These transmissions use both a TV cable and a Modulator Valve. Both items must work and be adjusted properly or the transmission will not shift correctly if at all. The modulator must connect to a Manifold Vacuum source. Proper adjustment of the 4T60 requires a pressure gauge and should be done only by qualified transmission mechanics.

Engine Conversion Note

The TV cable IS NOT optional. These transmissions WILL NOT shift right unless the cable is connected and working properly. On the 4T60 you must connect the modulator to a Manifold Vacuum source. Again, this cable IS NOT a “kick down” cable! It is used full time to control all shifting. It must move in sync with the throttle butterfly. If you connect it like a “kick down” that only moves at/near WOT then the TH125c and 4T60 transmissions will not shift right if at all.

Adjusting the cable correctly on the TH125c may require a pressure gauge, especially if you have to fabricate parts or extend the cable to connect it. You should not trust the built in adjuster to work by itself for many conversions.

Governor

The Governor Valve is part of the assembly that runs the VSS (Vehicle Speed Sensor) and is used with the TV cable to control shifting. If you’ve correctly adjusted the TV cable and still have late/no up shifts then this device may be dirty. If you attempt to repair this yourself be extremely careful! Damaging any part of the governor will screw up shifting. If you damage the springs in any way they MUST be replaced. The springs are calibrated items and the transmission will not shift right if they are out of whack. If you continue to have shifting problems after cleaning out the governor then you’ve got internal problems that will require tearing down the transmission.

Fluid & Filter changes.

There is a way to significantly reduce the mess associated with this job as well as get the maximum amount of old oil out of the transmission. I’ve used it a number of times and it works well. The transmission will stay oiled well enough to prevent damage but don’t take chances. Follow the warnings. This method will get a good amount of the oil normally held in the Torque Converter. The most oil I’ve gotten out of the Fiero using this method is 6.5-7 quarts of the 9 possible. Many people say you need to flush out the rest of the old oil. My feeling is that you only need to do that if the old fluid is burnt. If the old fluid is burnt then you likely need other major work done. Flushing is extremely wasteful for most situations.

WARNING! The following procedure can be dangerous. It should not be performed on a hot transmission. Use of proper
blocking and jack stands is a must. Do not allow transmission oil to run onto hot exhaust parts. This is not a GM approved method. There is the remote possibility you can damage the transmission. DO NOT shift the car from park during this operation! DO NOT allow the engine to run once oil flow has stopped.

DO NOT GET UNDER THE CAR WHILE IT IS RUNNING!

If you are uncomfortable with this then you could suck the oil out thru the dipstick tube. That will empty the pan but won’t get near the same amount of oil out. K-Mart Wal-Mart and others sell a small pump kit for about $10 that should work nicely for this job. (It will also make coolant work much less messy.) At K-mart they are in the auto section.

1. With the car raised on jack stands and the front wheels blocked. Disconnect the bottom cooler line from the transmission.
2. Install a temporary piece of line long enough to reach a catch basin under the car. Make sure the line is aimed so oil can’t spray out of the pan. The oil will flow at a small amount of pressure. Anchor the line in the pan so it won’t jump out.
3. Set the parking brake. If the hand brake doesn’t work then someone should stay in the car and hold the pedal tight.
4. Start the car and let it idle until oil flow stops. Shut off the car as soon as oil flow stops. DO NOT SHIFT THE CAR! DO NOT GET UNDER THE CAR WHILE IT IS RUNNING!
5. Let the car stand 5-10 minutes and then repeat step 3 one time.
6. Disconnect the top cooler hose and put the bottom line in a jar. Use low pressure, not more than 15-20PSI, compressed air to blow out the lines.
7. Reconnect the cooler lines to the transmission. (REPLACE the rubber lines if they are damaged or worn even slightly!)
8. Continue with the rest of the filter change procedure. Don’t forget to clean the magnet in the oil pan. (Note: Insert the filter bushing in the transmission then insert the filter neck.)
9. Take the car off the jacks.
10. When filling the transmission pour in 2-3 quarts of fresh Dexron III oil and start the car. Check the dipstick. Pour in more oil until the stick reads just below the full zone. (The oil is cold. You don’t want it to be over full when hot.)
11. Start the car and let the transmission warm up a few minutes. Put your foot on the brake and shift thru the gears. Check the fluid again. Drive it a block. Go fast enough for the car to hit third. (Don’t race!) Then recheck the fluid level one more time. Add more if needed to get the level to the middle of the full zone.

Notes

If the magnet is missing from the oil pan replace it. Any flat magnet(s) 3/16 to 1/4 inch thick will work. (Don’t use those thin “refrigerator” sheet type magnets. They aren’t very strong.) Just make sure it’s near the dimple in the pan used to locate the original magnet. That way it will be out of your way when you put the pan back on. The magnet is part of the oil filtration. It catches the iron flakes generated by the clutches.

When installing the filter put the bushing in the transmission opening THEN push the filter into the bushing. If you try it the other way it won’t go. The filter has changed over the years. Follow the directions included with the filter to alter the support clip on the older transmissions. If you forget this then the filter will obstruct the oil pan. I believe this only applies to 84-85 and maybe some 86 transmissions.

Dexron III

GM introduced Dexron III in 1995. Per GM literature Dexron III oil replaces Dexron II (and IIE) and is compatible with all GM passenger and light truck automatic transmissions built since 1949. (GM TSB 57-02-91 03-1995) It provides improvements to a number of characteristics and GM claims it requires no service. On cars that came with it, or freshly rebuilt transmissions, I could believe that but on older cars it should at least extend the service interval, especially in situations where it is likely to have some Dexron II mixed into it.

Yes, this means it is OK to add Dexron III to top off transmissions filled with Dexron II.

Dexron V? VI?

Near as I can figure there was some kind of issue with a Dexron V name. Some data and manuals for various things apparently call for Dexron V fluid. I’ve never seen it or been able to find it. At the time this document was last updated, the spec was being called Dexron V.

GM’s standard as of 2006 is Dexron VI and is listed as being backward compatible with all GM transmissions using Dexron fluids. Be warned that using this could void warranty or maybe damage other brands of vehicles. While it is rated for nearly all GM vehicles using Dexron that doesn’t automatically mean all others can use it. Check carefully.

How hot should the ATF run?

It should be running around 170-225F according to several sources. One of them
is here. (The BWD link to the nice table broke and I don’t have a copy…)

The Automatic transmission uses a heat exchanger in the radiator intake tank to cool the transmission fluid. The hotter the transmission fluid operates the shorter its life will be. At extreme temperatures the transmission itself will be damaged.

What many people fail to account for is the same heat exchanger makes sure the oil is hot enough to perform properly. With the TC locked many transmissions don’t generate enough heat to keep the oil properly hot in cool/cold weather. (This would likely be more of be an issue for long highway runs than city driving.) If you have a trans cooler installed after the radiator you could actually be shortening the life of your transmission because of this.

Transmission coolers

In general the TH125c and 4T60 should not need auxiliary cooling for most applications. However in racing and other heavy loads the stock heat exchanger may need help.

Most people don’t understand the function of the OE heat exchanger and as a result incorrectly install the aftermarket coolers. (Yes I know I’m repeating things here.)

The heat exchanger in the radiator is both a cooler and a heater. Transmission fluid must reach and maintain a certain temperature range to work properly.

The heat exchanger in the radiator makes sure that this happens even in freezing weather.

The engine coolant will often keep the transmission oil at operating temperature better than the transmission can by itself. Remember that when cruising down the highway, the TC is locked and there’s not much shifting going on. Under these conditions the transmission fluid can actually cool off too much to work without the help of the heat exchanger.

When you install an aftermarket transmission cooler, the device is installed upstream of the OE cooler. This insures that the transmission fluid will return to the transmission in the correct heat range.

If you install the aftermarket cooler downstream of the OE heat exchanger, or worse eliminate the OE heat exchanger, then the oil is likely to return to the transmission too cold to properly do it’s job. This can be almost as bad for the transmission as running too hot.

If you can’t tell which line to alter for the new cooler, disconnect one line from the OE cooler. (Top line is best in Fiero.) Bump the key for a second. If oil pumped from the line that is off then you’re new cooler will tap into that line.

Otherwise it will tap the one still on the radiator.

The Fiero TCC
(Transmission Solenoid Lockup)

by Chuck Kichline

http://www.kichline.com/chuck/fiero/TCC.htm
7/10/2008

I found out that there wasn’t a lot of information on automatic transmissions for the Fiero on the web, and even worse, both the Haynes and Clymer manuals are weak on diagnosis and had NO information on repair.  It became very important to me when my Fiero started staying locked up, stalling the car in traffic and endangering my LIFE!  Since the commercial manuals are no help at all, I started a search on the web, and finally found the information I was looking for.  Here is what I learned..

What is the lockup solenoid?  It’s an electrically operated valve in your Fiero automatic transmission that is controlled by the car’s computer.  When the computer believes it would be effective to lock the torque converter up solid it powers the solenoid which makes the transmission lock up.  The effect is that “fourth” gear that you sometimes feel on what is really a three speed automatic transmission.  The effect is better gas mileage, as it reduces the speed of the engine by about 250 RPM when it cuts in.  Not a whole lot, but good for a couple of miles per gallon.

What can go wrong?  Like all the other electronics on these cars, they can fail.  The failure may be that the lockup doesn’t happen, or that the engine stays locked up when coming to a halt, or blowing fuses.  If the lockup doesn’t happen it can mean poor gas mileage (18-19 mpg in a V6), the engine revving faster than it should, and possibly running warm or even overheating. Blowing fuses gets you the same result, since the lockup doesn’t work. Having the lockup stick on can be very dangerous, and leave you stranded in traffic in a car that won’t go into gear – or won’t properly kick down to pass.

How can I tell if my lockup isn’t working?  Do you occasionally feel what feels like a fourth gear?  Then it’s working.  If you want to test it, take the car up to about 55 on a level road, and press lightly on the brake pedal.  It should disengage the lockup, and with a steady foot on the gas, you should see the tachometer move up by about 250 RPM just as the brake lights go on. Another hint is that when coasting down from speed, it should disengage at 45mph – it feels like the car is speeding up on coast down, because when it disengages, the car starts freewheeling.

How can I tell if it’s sticking?  I had that fault, and it feels just like you forgot to put in the clutch in a manual transmission as you pull up to a stop light. The car stalls, if you’re lucky it will unstick and when you restart the engine. If you are unlucky like me, you’ll be stuck in the slow lane of the freeway with a car that will not move!  I finally got it out of traffic by revving the engine and slamming it into gear, and got out of the way in five foot jumps.  Not a good thing.  It had done it a few times before, but had always healed itself after the car died.  The previous owner had mentioned having some transmission work done, a “shift kit” (after I bought the car) and my guess is that she had had the work done only to find out that it still had the problem.  I guess that’s a good thing – otherwise she’d still probably be driving her car! What do I do if I have a problem?  If it isn’t locking up you are working your car harder than you should, higher revs and more heat.  You ought to fix it.  If it’s locking up and staying locked up, I suggest unplugging the lockup connector – that’s the green connector on the left front of the transmission “bell housing” behind the engine.  That will make it NOT lockup ever, and puts you in the no lockup mode.  It’s probably safer than getting caught in traffic and not being able to drive home!  If the transmission is locked up, the problem is probably in the solenoid being physically stuck or plugged, so just unplugging the connector while the engine is locked up doesn’t help, but it will keep it from happening again.

I risked trying the repair.  It turned out to be relatively easy, and I bet saved me several hundred dollars.  This is what I know, maybe you can do it too?

The lockup solenoid is under the cover on the left SIDE of the transmission. First we need to remove the cover.  From the top of the car remove the carb/aircleaner tube, the bolt that holds the transmission cooler hose (first arrow) and all of the bolts that hold the side transmission cover that you can reach from here (second arrow).

Here’s the solenoid connector that I mentioned earlier.  You don’t have to unplug it now if you haven’t.  See that the other stuff is now out of the way. Now jack up the car and pull the left rear wheel.  Put the car on a jack stand.

Remove the “tar paper” skirting between the inner fender and the frame.  It’s mounted mostly with reusable plastic pop rivets, just pull out the centers and put them back together to reassemble it with later. Tuck the skirting over to the side as you can.  Here’s the side cover from the wheel well. Looking down on the valve body after removing the side cover.  There should be just a little ATF in the side cover, so be ready to catch it when you take the cover off.  Pull the cover out the top.

OK,  here’s the valve body from the side.  The two wires come from the lockup connector.  Here’s the theory – there are TWO components in line. First the lockup solenoid then a pressure switch.  When the computer turns on the circuit it should close the lockup solenoid and the transmission should lock up.  In line with the lockup solenoid there is a pressure switch that is normally open, if the computer tries to lock up the transmission but there is not enough pressure the pressure switch is open and it doesn’t lock up – a mechanical interface to the transmission.

Those are the parts that I have highlighted.  If the transmission stays locked up, the problem is most certainly the solenoid and it should be replaced.  If it doesn’t lock up it could be either the solenoid or pressure switch.  Replace them both.  If it’s shorting, it could be either solenoid, switch or wires, check them all.  You may want to replace everything anyway, since it’s already apart. These parts are NOT going to be available from an auto parts store.  You will have to go to a transmission shop or dealer to get them.  I went to a transmission shop and was treated REALLY fairly.  You’re looking for the “transmission lockup (tcc) solenoid, pressure switch, and side cover gasket”. Ready for the cost?  About $20 for the solenoid, about $10 for the switch, and about $5 for the gasket.  YOUR PERFORMANCE MAY VARY!  Take the

side cover so they know for sure what transmission you have.  They’ll probably have to order the parts so go home and clean things up. I see that The Fiero Store stocks the solenoid now;  convenient, but at twice the price.

Here’s the inside of the cover – ready for cleaning.  Don’t forget to clean the old gasket off the cover and transmission body.

Here’s the solenoid out and sitting on the frame rail.  It’s held in by ONE T30 star screw.  I’d always used just a hex wrench before on these things, but it didn’t want to come loose so I bought a 3/8″ drive set with about seven different sizes.  It cost about $15 and those star screws are all over GM cars anyway.  It came out easy. Pull it down out of the valve body.  The pressure switch is a big hex, you may have to buy an “oil sender” type socket to remove it – it unscrews.

Here’s a real bad picture of the solenoid kit I used.  You cut the wires on the old solenoid and then use the quickie splices to install it.  The positive side of the solenoid goes to the wire directly to the lockup connector (and the negative goes to the pressure switch).  I’ve been told that the OEM solenoid comes with the wiring harness and connector.

Then you just put EVERYTHING back together.

So here it is all back together again.  I can say that I fixed my automatic transmission and it was relatively EASY!  Actual work time was only four or five hours.  I suggest that you change the fluid and filter now.  About six months after I fixed my TCC the transmission started slipping, but was fixed by changing the filter and fluid again (it had been changed before I replaced the TCC).  My guess is that the random lockup had kicked a lot of clutch plate parts into the fluid and they plugged up the filter.

I’d like to thank everybody that helped me, and hope that this helps others.

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