The A604 Transmission On The 1990-1993 Imperials

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There was only one tranny used on the 3.3/3.8L cars prior to the end of the AC/Y bodies in 1993. That tranny is the A604 (4-speed automatic with overdrive).

This was the first computer assist Mopar transmission for FWD cars, and had its own TCM (tranny computer). It is also the only tranny which will mate with the 3.3/3.8 and as a result, the 3.3/3.8L engine computers require the A604 tranny and computer in order to operate.

However there is a downside to the A604. It has been said that the A604 was built like a house of cards. In many ways, that is an understatement. So needless to say, there are unique instructions on keeping the A604 working, and a few ways (short of a rebuild) to get it working again.

Keeping the A604 Alive

To keep the A604 working, the tranny fluid and filter should be replaced every 80,000 miles or LESS, starting with the first 80,000 miles. Not doing so greatly decreases the life of the tranny- short of a rebuild. When this tranny was produced, Mopar had problems designing it so that it will fit on the FWD models (which at the time, had engines which sat transversely). So the result was sticking 8 cubic feet of parts in a 3 cubic foot tranny (the 8 and 3 foot sizes is figurative). This meant that the fluid must be very thin.

The thin oil would generally heat up faster, and because of the thickness restrictions, any small particles of dirt, gasket material, etc. in the A604 will do allot of damage. So the ONLY FLUID FOR THE A604 IS MOPAR 7176! NO OTHER FLUID WILL WORK WITHOUT GREATLY HARMING THE TRANSMISSION AND ITS INTERNAL PARTS!!!!!! This stuff can only be bought at the dealer, and is expensive. A complete fluid drain and fill is 10 quarts, which runs almost $90 (US). 5 quarts are all that are replaced during a filter and fluid change, and that's just around $40 (US, around $60 for the filter, fluid, and silicon gasket material).

Besides changing the oil and filter allot, it may also be helpful to use a tranny cooler on the car. That would keep the fluid from getting too hot, which will help keep things in shape.

There are also some "no brainer" rules which one must follow when using the A604 equipped cars. 1: Do NOT drop the car into drive from neutral or park while revving the car. 2: Completely stop the car before going to drive from reverse, or vise versa. 3: Do not commonly go to WOT then releasing the gas pedal completely- this will hurt the A604.

Fixing the A604's problems.

A majority of the A604 problems (hard shifting, staying in certain gears, etc.) can be resolved by simply doing a filter/oil change. This can, however, make things worse if the A604 had been neglected long enough, for enough miles without this simple oil/filter change. If changing the fluid and filter makes things worse, then a rebuild may be the only solution.

To change the fluid and filter, simply remove the oil pan on the A604 (sorry, but there isn't a drain plug, so you'll need something large, yet low to the ground to collect the oil when the pan drops). One way to do this is to remove all of the bolts except for on one side, then puncture the gasket on the side opposite the remaining bolts. This way, much of the fluid will pour out (as opposed to letting it surge out when removing all of the bolts at once). The new filter will snap right in place. The pan must be cleaned prior to putting it back on. Inside the pan should be a magnet which collects small metal particles which may be in the fluid. Clean out this entire pan, and the magnet, then bond the silicon gasket to the pan. Then simply bolt the pan back on, and put the new fluid in from the dip stick.

If you take your car to the shop (be it the dealer or someone else) for the A604 filter and oil change, be sure to bring up the need for using 7176 Mopar fluid ONLY. Some shops however, may (for what ever reason) disagree, and use Dextron 2, or some other fluid. Doing this requires a full tranny fluid drain and flush. This requires draining out all the oil, then pumping 10 quarts through the entire tranny to clean out the old stuff, then putting all new 10 quarts in. At about 10 dollars per quart, that's costly (but still cheaper then a rebuild!!).

It may become a good idea, if you plan on keeping your A604 car for a long time, to consider keeping a second, good A604 on hand as a spare. That way, if/when the one on the car goes, you can have a backup with which you can get your car back on the road. The A604 goes for +/- $600 (US).

This page was last updated on October 2, 2003.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club