In this article I will go over some of the tips and tricks that I have applied in order to keep the automatic transmission from failing, or prolonging it at the very least.
Torque Converter and Fluid
Lets start with the fluid, the transmission fluid is one of the most important parts of the system, it is used to transfer the engines output to the wheels. The engine spins a large drum called the torque converter. The converter is bolted to the flex plate (it is like the flywheel on a manual car), which is connected to the engines crank. The converter has an output in the center which connects to the transmission; this output is physically separate from the housing. An example of how the converter works is when you put two fans facing each other and you turn one on, the other one will spin. Of course the internals of the converter are more complex but it is the same principle.
You can start to see why you are able to have an automatic car in drive while at a stop, yet in a manual car the engine would stall if you left it in gear and stopped. This is because at low RPM’s the converter is not spinning fast enough to cause the opposite side (the output) to spin and propel the car forward, this is called the stall speed; it is the RPM which the engine begins to stall due to the transmissions resistance. Typically on a factory car like the Maxima the stall speed is around 1500 to 2500 RPM. In racing conditions where you want to launch the car as quick as possible, you want to do it from a high RPM. This is when you hear “high stall torque converters” being mentioned. With a high stall converter, the internal fins are modified and angled so that the RPM needed to move the car is higher.
You may think that you can put the highest stall possible but this comes at a cost. The higher the stall the less efficient the converter may be because there is less room for the converter to couple before the rev limit. The coupling is when the input and the output of the converter are spinning at near 1:1 ratio. The lower the RPM the less coupling, the more the RPM the more coupling and more torque is transferred to the wheels. Having the stall too high may give a similar symptom as when you drive a manual with a slipping clutch, you never get the full engagement.
Lock up converter
Torque converters have the option of a lock up clutch that engages using a solenoid on the Valve Body. When this clutch is engaged the converters input and output are locked together functioning just like a manual clutch. With a 1:1 ratio all the engines torque is transferred to the transmission. The ideal torque converter is that which gives you the highest stall possible while coupling still within the engines most usable RPM range. Using the lock up clutch may not be ideal depending on the application; they may not be able to hold the torque on higher HP/TQ. On a high quality converter the coupling should be enough to where a lock up clutch is not needed. Usually the lock up clutch is used by factory during cruising conditions. You may notice the sense of an extra gear when you come to a cruising speed at 40mph to 60mph, this is because the clutch engages and RPM’s drop for better gas milage. Also at wide open throttle with the shifter in Drive and the OD Off (light on the dash turned on), this will keep the transmission in 3rd gear and also lock the torque converter; you can play around this to get a better feel for it.
A 3,000 to a 3,500 stall is usually ideal for most Maxima applications.
Fluid
Keeping the fluid temperature under control is critical. The transmission not only uses fluid in the torque converter but uses it in the entire transmission. Fluid flows through a central location called the valve body. The valve body is what directs the fluid through passages using solenoids to output to the necessary clutches and bands for the selected gear. In factory form, the transmission a has fluid hose output that goes into a bottom chamber of the radiator, exists and then returns to the transmission. This is great to warm up the transmission during cold starts as well as keeping the temperature from overheating by being influenced by the coolant temperature. The problem is that when the torque is beyond what the car came with, you are increasing heat, the radiator’s transmission chamber is not good enough to keep the temperature down.
An external cooler is then required, in my opinion this applies to even maxima’s that are kept in stock form. It is well known that heat is one of the main causes of failures, so why not address it immediately. The external cooler choice varies, I always say to get the largest cooler you can fit. If you live in an environment where freezing temperature are expected it is always a good idea to use a thermostat combined with the cooler.
In this picture above, you can see the inlet and outlet of the fluid. The large banjo fitting is the outlet and the hard line above it is the return. The hose used is a 3/8th transmission hose.
The cooler I used is a Tru-cool that is rated for 40,000 GVM (gross vehicle mass) and is generally used in RV and Towing applications. Mounted on the cooler are two Spal 9inch puller fans which I have mounted on a switch using relays.
You can find the cooler and fans on amazon.
Cooler: https://amzn.to/2LJRu8v
Fan: https://amzn.to/30XaTXm
Clutches
Inside the transmission there are severals drums with shafts going through them that spin freely independent from the body of the drum. To help you think about this imagine a rod connected to the engine which goes through a drum. The body of the drum is connected to the wheels. So the engine and the wheels are independent because the engines shaft spins freely. Now if you were to connect the rod with the drum then the wheels would turn. In the drum there is an alternating stack of disks (or clutches. One set of clutches is connected to the housing while the other set is connected to the shaft. When you press them together the friction binds them so the shaft and the drum spin together transferring the engines torque to the wheels. The clutche pack is submerged in fluid which allows for an important function. It keeps the disks from burning by keeping them lubricated and gliding against each other till they are pressed together; rubbing your hands dry vs. rubbing them with soap. This is called viscous coupling, where fluid is used to transfer torque. When you press the plates together using hydraulic pressure, the plates will slip till there is enough force and resistance to make them connect. During this engagement a lot of heat is generated, so you want to engage as quickly as possible to not stay in the slipping stage too long.
Driving Habits
To extend the life of the auto I go by a couple of rules I set myself. Never go wide open throttle from a roll while the transmission is in a higher gear. Putting load on the transmission while it is downshift is very rough on it. It generates a lot of heat because there is more slippage in the clutches. It is better if you manually downshift to a lower gear before going wide open throttle.
When driving and racing I like to keep an eye on the transmission temperature. I like to keep the temperature below 185 at all times. You will notice that while in traffic the temperature will start climbing up, this is because the converter is constantly spinning trying to get the car to move but you are creating resistance by being at a stop; this produces heat. I sometimes prefer to put the car in neutral when at a stop for a long time such as a staging line at the track or traffic.
Modifications
Drop Resistor Mod
This popular modification is also very important because it increases the fluid pressure that the transmission uses internally. This means that the clutches in the transmission are pressed together with more force and therefore providing less slippage and more engagement. Usually factory cars come with a certain amount of slip in order to provide for a smooth comfortable ride, but since we want to go fast here we want the most clamping force possible..
The drop resistor modification is simple, there is a resistor that is mounted on the driver side strut tower in the engine bay on 4th gen and 5th gen Maxima’s, (6th gen perhaps?). When this resistor is disconnected, the transmission then will use 100% of the fluid pressure available. Since disconnecting this causes higher pressure and we want this, you can get a throttle switch that is Normally Closed. The switch can be placed at the throttle or below the gas pedal. You want to activate the switch when you are at open throttle, this will disconnect the resistor. You do not want to disconnect the resistor all the time or at low part throttle because you will have a violent shift that may cause some damage. Note that your overdrive lights will flash when the resistor disconnects at open throttle; the light and code will go away over time and does not affect drivability.
Valve Body
The valve body is responsible for the behavior of the transmission. Attached to the valve body there is a pack of solenoids. In the pack includes two shift solenoids (in the case of the 4 speed Maxima), a fluid pressure solenoid, a torque converter solenoid and and overrun clutch solenoid. When it comes to modifications you have the option to upgrade the VB yourself using a Transgo shift kit. There is the HD and HD2, the later being a more aggressive change in the shifts. There are passages that are drilled as well as ball bearings and springs that are changed to affect the pressure the clutches in the transmission are getting.
Another option is sending the valve body to a transmission shop for them to upgrade, there are common modifications done to automatic performance transmissions so most auto shops should be able to do this.
The solenoids are sometimes also upgraded, they are modified to increase the amount of fluid that flows through them which help add pressure on the clutches and bands.
Internals
The internals of the automatic 4 speed Maxima transmissions which include the clutches and bands mentioned are very good in stock form. I cannot say the same about the 5 speed automatic nor the 5 speed manual. The internals of the transmission can be upgraded by replacing the clutch packs with superior quality as well as the bands. Sometimes more clutches are added to the stack provided the overall height of the stack does not pass the required specs. The clutch in the torque converter can also be upgraded to a stronger material such as carbon so that it has more gripping strength and longer life.
Racing
Lets talk about a turbo automatic maxima and how one can get the best out of the transmission in a drag racing application. You want to take off as fast as possible from a stop. With a turbo automatic you want to have a high stall converter so that the RPM’s required to get the car to move are higher, this allows for the turbo to get enough exhaust flow to generate some boost. So from a stop you press the brakes firmly and at the same time you press the accelerator partly. The RPM’s will start to climb till they reach the stall speed, you will hear the turbo start to wake up. Depending on the stall you have you will be able to generate boost from a stop, then to launch you let go of the brake and go full throttle. Note that this generates an enormous amount of heat in the transmission fluid and causes a lot of wear. This is called Brake Torquing or Brake Boosting on turbo cars.
Another option one can experiment with is using the lock up of the converter during a race. On an all motor Maxima you can lock the converter at the top of second gear and third gear, this varies but is it a general idea and you should experiment with your own application. You want to keep it unlocked in first so that you have the quickest revs and launch possible. Like mentioned before, when you have a good quality and well tuned torque converter you will not need to use the locking mechanism.
Nitrous can be very effective on an automatic turbo car. In my case I have always been a fan of nitrous and have been using Dynotune for many years. I use the nitrous to launch the car without having to brake torque too much. I do not like building up the heat while at the line waiting to take off because then that heat continues to rise as I go down the track. Instead I lightly brake torque to get the turbo spinning a bit then at launch I spray the nitrous.
I thank you for taking the time to read this entry and hope you found it valuable.
If you are interested in nitrous I will be publishing an article soon, meanwhile check out the nitrous kits available in the shop.
