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Peformance/Improvements/Modifications
Ok, basically the A604 is a nightmare. Its an automatic 3speed with a 4th gear for overdrive.
The tranny uses hydrolics to operate internally, which are controlled via 4 solenoids and a manual valve body. The solenoids, being electrical, means that the tranny is electronically controlled (through a computer- the TCM).
Thus you have two seperate things to worry about in troubleshooting or modifications: The electronics, and the physical mechanical aspect of the tranny.
Depending on the year, the A604 used one or two speed sensors (diagram above shows two- the turbine speed sensor and the output speed sensor). These sensors do die or becom inacurate with time, and when they are not acurate enough - they will cause limp mode (more about that later).
The TCM uses inputs to determine how to control the A604. It uses the PRNDL switch, solenoid pack, tranny speed sensor(s), TBPS (throttle body position sensor), crank sensor (rpm's of the engine) and so on. If any of these inputs have a problem, the TCM will control the A604 improperly.
The TCM also "learns" how the driver uses the car and is what I call a "smart computer system" as it (unlike, say, the PCM with a pre-burned ROM) uses memory to record info on the driver's habbits, the idea being that it could allow for smoother shifting.
In practice a perfectly operating A604 does give extremely smooth shifting, however the system was ahead of its time and thus does not always operate as planed.
Most models that got the A604 (like the Dynasty) had a tranny oil cooler circuit within the radiator. Basically the A604's fluid is sent out (in rubber hose) to the radiator, and goes through its own piping/cooling system within the radiator. Some models (vans with certain options packages, etc) got an external tranny fluid cooler from the factor (like a mini radiator).
As the A604 and TCM were refined over the years, the TCM got several changes including the ability for the dealer to "load" onto the TCM the software used for shifting. This is nice since the newer versions of the code are better for the hardware.
The solenoid pack consists of some pressure switches that can trigger limp mode (when something in the A604's hydrolic system goes wrong) and 4 solenoids. A solenoid is a electronic coil which, when given voltage, will generate a magnetic field. This field "moves" a small plunger-shaped section of metal, which in return, allows fluid to go through the solenoid. The most common example found in cars is a fuel injector.
In this application, a manual valve body (the thing that is turned with a steel cable when you touch the shifter handle) switches the A604 between "P R N D 3 L" (d= overdrive). When this happens, the manual valve body manually (physically) switches the path and direction of the fluid on its way to the solenoids. Thus what controls what gear you are in is both the solenoids in use and the direction of the fluid going to the solenoid.
THE A604 CAN ONLY USE ATF3 OR ATF4 DEPENDING ON THE YEAR. THE PRE1999 MODELS CAN USE ATF3 OR ATF4 WHILE THE 1999 & NEWER MODELS CAN ONLY USE ATF4.
ATF4 IS ONLY SOLD AND MADE BY CHRYSLER, THERE IS NO GENERIC VERSION ANYWHERE ELSE ON THE MARKET. DO NOT TRY TO USE ATF3 OR VALVOLINE ATF3 IN YOUR LATE MODEL A604, IT WILL NOT WORK.
IN TERMS OF ATF3, CHRYSLER NO LONGER MAKES IT HOWEVER THEY LICENSED THE FORUMLA OUT, MANY COMPANIES NOW MAKE A GENERIC ATF3. THIS HAS BEEN KNOWN TO WORK PERFECTLY FOR SOME PEOPLE, AND CAUSE SLIGHT PROBLEMS WITH OTHERS.
YOU CAN NOT, EVER, NO MATTER HOW YOU TRY OR WHO SAYS OTHERWISE, USE DEXRON OR DEXRON + AN ADDITIVE IN YOUR A604. IT WILL KILL IT!!!!
DEXRON IS NOT TO BE USED IN THIS TRANSMISSION, AND YET EVEN IN 2006 SOME SHOPS WILL CUT CORNERS AND USE IT SINCE IT IS ALOT CHEAPER. BE SURE YOU AND YOUR SERVICE PERSONAL ONLY USE THE CORRECT FLUID, AND NEVER, EVER, EVER DEXRON.
THE MOPAR COMMUNITY FOR ALMOST A DECADE HAS BEEN SAYING IN THE MINIVAN, PROWLER AND INTREPID GROUPS THAT DEXRON + AN ADDITIVE IS NO WHERE NEAR BEING ATF3.
IF YOU ARE UNSURE WHAT FLUID IS IN YOUR TRANS, TAKE IT TO A DEALERSHIP AND HAVE IT FLUSHED AND RUN ATF4 OR ATF3.
IF YOU FAIL TO ADHERE TO THIS IMPORTANT FLUID NOTE, YOU HAVE BEEN WARNED.
Not unlike most automatics of this period, the A604 does use lockup- which is turned on/off by the TCM by modulating a 3rd solenoid (most gears use 2 solenoids...).
The solenoids operate @ 140 Hz (35 % duty cycle). When the lockup solenoid is modulated, basically the duty cycle is being varried. This is a square wave (On OR off) and thus the duty cycle in this context, is how long the "up" part lasts (while 140hz is how often it turns on).
To help protect against mechanical damage, the system is designed to electronically turn on "limp mode" when something is wrong. Basically the solenoid pack is turned off in limp mode (either by the pressure switches shorting it to ground or the TCM turning off its +12 volt power supply).
Limp mode I have also had from mechanical problems that the TCM nor solenoid pack shouldnt be able to notice (like broken engine and tranny mounts).
The TCM also stores "fault codes"- not unlike the TCM. You ***cannnot*** read these codes from the ignition switch of the car, you must get a Mopar TCM reader and plug it into one of the diagnostic ports on the car (in the AC/AY- there is one in the engine bay and one near the emergency brake release- its a blue terminal).
There is a circuit out there for a DIY TCM code reader, which can be found here: http://www.kolumbus.fi/juha.niinikoski/CCD_bus/ccd_display.htm
I have yet to try the circuit so I can not speak to its quality, but it does look promising.
To erease the fault codes, you could either get the diagnostic reader unit OR unplug the battery for a few days. If you can afford it and plan on owning your car for a long time, a diagnostic reader maybe a cool toy since it is helpful for working on your TCM, BCM or PCM circuits. This is all preOBID2 mind you- stuff changes in 1994....