AXOD-E/AX4S

[ Written by: Qwertz9586 ]   [ First Posted: September 2, 2006 ]   [ Last Modified: February 02, 2010 ]

The following is a collection of tips and advice I've picked up on the TCCA Forums as well as personal experience. I've put them all together into an easy to read article for everyone so you don't need to be an expert to understand what's going on. Thank you to all the technicians, mechanics, owners, and drivers who shared their advice, technical knowledge, and experience about this car. Without them, this article wouldn't be possible.


The AXOD-E/AX4S transaxle used in the Taurus/Sable is a 4-speed automatic overdrive transaxle (meaning it has the transmission and differential in the same unit). It was introduced in 1991 and is an electronically controlled AXOD. It was used in the Taurus/Sable until early 2003 and was replaced by the AX4N.

The AXOD-E/AX4S is a synchronous transaxle which means the internal clutches engage at the same time. This means you can feel the different "gears" as it shifts sequentially. It is the weakest link under the hood. Because of its weakness, you have to be extra careful and take extra precautions to keep it lasting long. Some simple precautions you can take is just change the transmission fluid more frequently than recommended, use synthetic transmission fluid, and install an auxiliary transmission cooler. It's mainly the heat that kills most transaxles because the transaxle sits in a cramped spot under the engine so there is little heat dissipation. The heat also depletes the additives that are in transmission fluid which makes it less effective in the long run.

For more detailed information about how an automatic transmission works, please refer to the How Stuff Works article on automatic transmissions.

What Not To Do

Knowing how to drive the car efficiently is also a big help. I know everyone wants to go racing in their car, but that's just not the right thing to do. Neutral bombs (putting the shifter into neutral, revving the engine, then drop it into gear) are like playing Russian roulette. You may be lucky and still have your transaxle, but you don't want to be unlucky and shoot a piston through your transaxle pan and wiping out the gears with it. Brake torquing will heat up the transmission fluid and that's what you don't want to do either.

Now that the obvious is out of the way, let's go on to the not so obvious things. These transaxles are slow to shift. You might have noticed it when it shifts from first to second. Personally, I would take it easy and not go above 2000 RPMs when it's shifting from first to second. You can go a little higher, but don't go excessively high (like past 5000 RPMs). Once it completes the first to second shift, the other gears are a lot more firm and quick. The reason for this is because it does the first to second shift a lot more often than the other shifts thus wearing it out faster. It gets sloppy over time and becomes the most noticeable. Just take it easy until you get out of first.

Speaking of slow shifting, it doesn't just apply to the forward gears. When you move the shifter manually it will also shift slow. Like when you shift from Park to Reverse, Park to Drive, Reverse to Drive, etc. The most noticeable "lag" is the Reverse-to-a-forward-gear shift and vice versa. It seems to take the computer a while to think about the decision. On the older cars you can feel it clunk into gear when it's ready. The newer ones have a softer shift, but it still takes a while for the computer to change the gear. You should wait a second or two before taking off. You should always come to a complete stop before moving the shifter. If you let it roll and then add gas while the computer changes gear, you end up doing a mini neutral bomb.

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Torque Converter

This section is just here for reference. Tips and advice about how to manipulate the torque converter are in the Overdrive vs. Drive section. If you are interested in learning about the torque converter, then I recommend reading the How Stuff Works article on torque converters for a more in-depth look at a torque converter and what it does in an automatic transmission.

So basically the torque converter (T/C) is a fluid coupling between the engine and transmission that allows the engine to spin freely when the car is stopped in gear and allows the engine to send power to the transmission when you release the brake pedal or hit the gas pedal. It's kind of like an automatic clutch. A neat feature of the T/C is the automatic lockup. In the AXOD-E/AX4S, the automatic lockup is electronic and is controlled by the computer. It reduces slippage between the engine and transaxle which results in better fuel economy at highway speeds.

The T/C in the AXOD-E/AX4S will lock up in third and fourth (Overdrive) at around 1500 RPMs. The lowest speed the T/C will lock up at is 30 MPH and the lowest speed it unlocks is at 25 MPH. If you're driving around the city and you release the gas pedal, it will automatically unlock. I don't really see a valid reason as to why it does this. If you feather the pedal (slowly reduce the pressure on the gas pedal), it won't unlock. When it locks/unlocks, it will look like a shift on the tachometer, but you won't feel the harsh bump that's normally associated with a shift. The RPMs go up by about 500 RPMs when it unlocks, and the RPMs go down by 500 RPMs when it locks. This is normal. It will also unlock first before downshifting you add gas at cruising speed (such as going up a hill or want to pass another car) and lock back up after you get back to cruising speed. You can get an expensive chip for the computer to re-program the T/C's locking and unlocking abilities (such as staying locked up once it locks up until you hit the brakes) if you really don't like the stock programming.

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Overdrive vs. Drive

Now for us normal people, we have to decide if we want to use Overdrive or regular Drive. Is there really a difference? Well, yes and no. They are pretty similar until you get into third. That's where the difference is. Drive just locks out Overdrive. Overdrive has another shift and the torque converter will lock and unlock depending on load. Overdrive brings down the engine's RPMs so that the engine is spinning slower than the wheels are spinning to save on gas. Normally, the transaxle will shift into Overdrive at a speed greater than 40 MPH. You're probably wondering, "When should I use Drive and Overdrive?" Well the owner's manual recommends you to use Overdrive for all your normal driving and use Drive for hilly terrain and hauling heavy loads. I have a different perspective. I use Overdrive strictly for highways or any long roads with no stops. I use Drive for daily city driving.

For example, my daily commute includes driving on a main city street with many stoplights and traffic. The speed limit varies between 35 MPH and 50 MPH depending on what stretch I'm traveling on. It also has a combination of flat road and hills. I usually put the shifter into Drive because of the hills and traffic. When I get on the interstate or a long road I'll pop the shifter up into Overdrive. When I get back on to city streets, I'll pop the shifter down into Drive (unless I know I'm not going to go above 40 MPH).

Now you're probably thinking, "Why should I use Drive when Overdrive saves gas like you said above?" Well, I performed an experiment over a couple months (same gas, same weather, and same route), and I discovered that I lost 0.5 MPG from using Overdrive on my daily commute due to the excess shifting. So even if Overdrive runs at lower RPMs, the torque converter locking/unlocking plus the extra shifting nets worse gas mileage than just letting it run at a higher RPM all the time. It also doesn't make sense for it to shift into Overdrive just as the traffic light ahead of me changes to yellow and red. The extra shifting (into and out of Overdrive) will increase the heat in the transaxle. I'd rather pay a little extra in gas than to pay $2000-4000 for a new transaxle.

Another reason why I like using Drive on city streets is that it puts the RPMs in the peak power range! So I'm cruising at 50 MPH and I want to pass someone. Well instead of waiting for the transaxle to downshift to get the engine in the power band, I can just gradually add gas and pass. The max torque range is around 2000-3500 RPMs for the Vulcan and Essex (the two engines that are commonly hooked up to the AXOD-E/AX4S) so it's easier to add gas gradually and slide into the power than to wait for it downshift harshly and rev past the power band. In a way, you might be saving some gas from not having to downshift.

When I'm in Overdrive and I add some gas I notice that the T/C will unlock before it downshifts out of Overdrive because I see the RPMs jump up by 500 RPMs (the actual shift out of Overdrive will feel harsher and have a higher RPM jump). It will also stay in unlocked Overdrive for a couple seconds before downshifting into Drive. If I leave the shifter in Drive, the T/C will stay locked because the RPMs are high enough to keep it locked and it is a little harder to make it unlock unless I really pound on the gas pedal. This means I don't have to wait for that intermediate step in downshifting so I get the power instantly.

Drive also offers some engine braking (where the engine's compression slows down the vehicle) at city speeds (around 40 to 60 MPH). I've noticed that Overdrive doesn't have engine braking unless I'm going more than 70 MPH (on the highway), but as soon as I slow down to below 60 MPH, it starts to coast for a long time with very little speed loss (I'm assuming that's when the T/C unlocks in Overdrive). I can coast down a hill in Drive at the city speed limit (and slow down slightly) while the other cars are riding their brakes. I can also coast in Drive to a traffic light and slow down faster than other cars that have to hit their brakes earlier.

I do agree with the owner's manual about using Drive on hilly terrain. Having driven up a mountain in Overdrive not knowing about turning off Overdrive for hills, the transaxle will shift all over the place because the computer is trying to get into the power band to climb the mountain and then it tries to "save gas" and shift into Overdrive when it detects the slightest decrease in gas pedal pressure. It repeats the sequence many times up the mountain. The shifting wears out the transaxle's bands and clutches faster and also generates a lot more heat. Leave it in Drive and it's always in the power band and it saves the transaxle from wearing out quicker. You can try and use Overdrive to go up hills without it shifting, but you need to speed up before you hit the hill and then allow it to lose speed naturally uphill and be more patient with it. Other drivers might get irate at you and you are going to get up the hill slower so that's why I recommend you to just use Drive. Using Drive instead of Overdrive also applies to towing or carrying heavy loads regardless of hills because of the engine braking and optimal power.

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First Gear

First gear is mainly used for going up and down steep hills. It offers engine braking going downhill while keeps the engine in the torque range for better climbing. As long as you don't exceed 30 MPH, it should be fine to use. Locking first gear is also great for premature failure in rush hour or in parking lots since it likes to shift between first and second gear a lot in low speed stop-and-go. I wouldn't recommend shifting into it while the car is in motion. It's a rather harsh shift. It's also not a direct linkage into first gear. If you're going fast enough, you can pull the shifter into first, but it'll only downshift into second so the transaxle won't blow itself up. See, the computer can be smarter than the user sometimes. I wouldn't recommend doing it often though because that's mainly for engine braking going down a hill. Once it gets to a low enough speed, the computer will lock the transaxle into first until you move the shifter again.

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Park and Neutral

There are some things you ought to know about Park and Neutral. There is a rev limiter for Park and Neutral that limits the engine's RPMs to 4000 RPMs. This is to prevent the engine from blowing itself up because of an ignorant user. In the other gear selections the computer raises the rev limiter (somewhere around 5500 to 6000 RPMs), but there's also a speed limiter that will cut the engine's power at a predetermined speed (somewhere around 110 to 115 MPH).

Neutral is interesting. It doesn't seem like it's doing much but allowing the wheels to spin independent of the engine. Now if you were moving at 60 MPH and you popped the shifter into Neutral, you'd expect the car to keep rolling (maybe slow down a tiny bit too), but have the engine's speed drop to idle, right? Wrong! If you're going 60 MPH and put the shifter into Neutral, the RPMs will stay at where it was before when the transaxle was in gear (the RPMs might even jump up higher). This is a feature so that the transaxle won't tear itself apart when you put the shifter back into gear. Now, if you tried to shove the shifter into Park, you'll just get a rapid clicking sound and slow down quickly until 20 MPH. At that point the front wheels will proceed to lock up. I highly recommend not putting the shifter into Park when the car is in motion. I believe the computer also has enough sense to not allow the transaxle to go into Reverse when the speed is high enough (don't try it if you value your transaxle in case I'm wrong about the computer's programming).

Park is not a substitution for the parking brake! Never leave the car without setting the parking brake! Think about it. In Park, the only thing stopping your two ton car from rolling away is a metal rod the size of a pencil. That's not real reassuring. The parking brake takes a lot of weight off that metal rod so that you can shift in and out of Park much easier and it doesn't stress the transaxle more than it needs to. Always set the parking brake before going into Park. There have been stories about cars slipping out of Park or Park failing so spend that extra couple of seconds and push down that pedal.

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Summary

Below is a list of the main points in the above sections. They are listed in order of importance. Please refer to the sections above for more details and examples regarding this list. Click on the keywords in the list to visit the respective section.

  • Install an auxiliary transmission cooler as soon as possible, and change your transmission fluid on time (every 30,000 miles under normal driving conditions or every 15,000 miles under severe driving conditions and check your owner's manual for correct fluid type).
  • Do not do any neutral bombs or brake torquing.
  • Do not put shifter into First, Neutral, or Park while the car is in motion.
  • Set the parking brake before shifting into Park, and do not use Park as a substitute for the parking brake.
  • Wait a second after coming to a complete stop before shifting into another gear, and wait a couple seconds for the computer to find the correct gear.
  • First to second shift is the worst. Lock the shifter into First if you are travelling at an extremely slow speed (such as in bumper-to-bumper traffic or in parking lots with speed bumps) to prevent more wear and tear.
  • Use Overdrive if you are constantly cruising above 50 MPH for more than 10 minutes (such as on a highway) for maximum fuel efficiency, but do not use Overdrive on hilly terrain.
  • Leave the shifter in Drive if you are travelling in stop-and-go traffic that does not exceed 50 MPH. Gas mileage will suffer slightly from using Overdrive in the city.
  • Anticipate stops and try to coast.

Well, there's a nickel's worth of free advice for you. Remember, most front wheel drive transaxles have similar overheating problems so it's not just the AXOD-E/AX4S. Most of the techniques can possibly apply to other transaxles too, but with slight variation based on the computer's programming. Take good care of the transaxle and it'll reward you with a longer life. I hope this write-up answers a lot of questions.

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