TCM

Not all of them could be flashed. Installing updated software was to address about ten common complaints for customer satisfaction. For example, my 1993 Dynasty has a minor case of "bump-shift". That is when it takes too long to down-shift into first gear when slowing to a stop. It only causes discomfort when starting to accelerate just as it is going into first gear. A rolling stop is when that occurs. In my case, the transmission computer could not be updated, so I had to install one under warranty that could have new software installed. Trouble is that did not solve the issue, so I just live with it. That car does not have 5,000 miles yet, so it really does not pay to worry about it.

This computer-controlled transmission was another in a real long string of innovations from Chrysler that had real benefits for car owners. There is a major drawback though. Up until 1988, all automatic transmissions were hydraulically-controlled. Shifting was done based on a battle between road speed and throttle position. Under hard acceleration, higher road speed needed to be reached to initiate an up-shift. As the clutch plates wore, more fluid needed to fill in behind them to apply the pressure that made them engage. With excessive wear, we would get "engine runaway" between shifts, meaning engine speed would flare up, then come back down when the clutch pack finally locked up. That runaway gave us a good two years warning that a rebuild was in our future.

With Chrysler's computer controls in 1989, the computer watches the volume of fluid it takes for a clutch pack to fully engage. With high mileage and lots of wear, the computer learns that it needs to engage third gear, for example, then wait a little longer before it releases second gear. Due to that increased overlap, the driver feels the same nice crisp shift like when it was new, up until the day when it cannot update any further. That is when excessive slippage is detected and the system goes to "limp" mode where it stays in second gear until the ignition switch is turned off, and the engine is restarted. The drawback is we do not get those years of warning that wear is taking place.

The slippage is detected through the input speed sensor and the output speed sensor. The computer knows each gear ratio, then based on input speed, it knows what to expect for output, (half shaft/tire) speed. If those two do not agree, it is because one of the clutch packs is slipping. It will set a diagnostic fault code indicating the defective condition.

It is possible to read the "clutch volume index", (CVI), on a scanner. That is a set of four numbers indicating the CCs of fluid it takes to apply each clutch pack. An experienced transmission mechanic can tell from those numbers how much life is left in the transmission.

When you disconnect the battery or the computer, everything in memory is lost, including those CVI numbers. It can take up to two miles or a dozen shift cycles for that data to be relearned. That applies to your new computer too. Until it relearns the personality of your transmission and its various sensors, the transmission could shift like a race car, or it could have mushy or sloppy shifts. The same thing happens when you get a new battery installed. Many mechanics will take your vehicle on a short test-drive to do the relearn, otherwise, they are supposed to explain to you the need for that to take place. The relearn can also be done in the shop with a Chrysler DRB3 scanner. I have one of them for all of my vehicles, but it is only my Dynasty that will sit for long periods without a battery. When I do drive it, there is nothing noteworthy about how it shifts at first.

Road speed and rate of acceleration are still factors in calculating shift points, but those can also be tweaked for air temperature, whether the AC compressor is cycling on and off, and other variables. (Cold transmission fluid does not flow well to the cooler). The torque converter will not lock up for better fuel mileage, (another Chrysler innovation from 1977), until the fluid is up to normal temperature. That helps it get to normal temperature faster when the fluid is cold and thick. The computer can also inhibit overdrive gears when the fluid is cold, again, until that fluid can flow easier.

To answer your question about sticking in a new computer, it is going to run your transmission just fine as is. Unlike the newer engine computers that must have the appropriate software installed, and that can only be done by the dealer, (that is a GM innovation that only benefits GM's bottom line), any updates that you could have done only apply to customer satisfaction issues, not to the actual operation. This new computer will work exactly the same as after you disconnect the battery for some other service. By the way, my daily driver is a rusty, trusty, 1994 Grand Voyager, and I have a 1995 Grand Caravan waiting for when I need it. Next time you need a computer, you can use one from a salvage yard. That is why I am still driving these old vans. GM figured out how to make their computers not work in a different vehicle so you have to buy new ones from them. That is why none of my friends own newer GM products.

First lets clear up some terminology. Flashing the computer means installing the software so the computer will operate the circuits on the vehicle it's being installed on, or installing new, updated software. Think of that as installing an operating system on a new hard drive for your computer. Until that is done, the module is stupid and cannot do anything.

When you talk about pinion factor and tire size, those are just variables entered or changed when necessary to match your car to make the speedometer read accurately. A flash is downloaded from Chrysler, either over the internet or over a satellite dish, into a scanner, then the scanner is connected to the car and that flash is uploaded into it. The scanner is used as a "stand-alone" scanner to change customer preferences through drop-down menus. I can do that in my driveway with my Chrysler DRB2 and DRB3. Customer preferences are things like the horn chirping when you lock the doors, doors that lock automatically at fifteen mph, and things like that. Pinion factor refers to the final drive gear ratio, same as the gear ratio of a rear differential. Often there were two choices available, and sometimes three, when the car was built. A certain gear ratio might have been part of an optional package. Same with tire sizes. Rather than build different transmission computers for every possible combination, they make just one part number, then program in the variables. That means fewer parts to keep in stock, and it is easier to find the right computer in a salvage yard.

Your new computer likely came pre-programmed with the most common tire size and pinion factor. If the speedometer appears to be reading incorrectly, you will need a scanner to see what is programmed in and what needs to be changed.

Your "hairy magnet" is normal. Would not be needed if there was nothing to collect.

For the symptoms you listed, it is best to have a conversation with a transmission specialist. I doubt that is related to the computer because even with a total failure of the electrical part of that system, the shift solenoids are spring-loaded to give you park, reverse, neutral, and second gear. That is limp mode. If you did not even have second gear, that would more likely be a pressurized fluid issue. Additionally, low fluid pressure will cause the clutch packs to fill and apply too slowly, which could cause slippage during up-shifts.

As a point of interest, there was a recall around the early 1990's to install a transmission fluid cooler bypass valve. In cold weather, the fluid could get too thick to flow through the cooler properly. That returning fluid did not just dump back into the pan. It was used for something important, and the bypass valve was to insure whatever that was, it did not starve for fluid before it had warmed up. I do not remember what the potential symptoms were.

On the few radiators I pulled apart for scrap metal, the cooler was a brass cylinder about ten inches long and perhaps 1 1/4" in diameter. I don't know what's inside that cylinder. I've also seen photos where the cooler was nothing more than a coiled piece of metal tubing that would probably be two feet long when stretched out. Consider that if an application requires a more-substantial cooler, it will be a small radiator mounted right in front of the radiator. Those are mostly cooling fins and not much tube. I wouldn't expect to get much fluid out of any of them.

Remember too that while transmissions reach the same temperature, around 200 degrees, that engines do, engines develop a real lot more volume, or BTUs. A candle gets a lot hotter than a car engine, but the engine needs a lot more cooling area of the radiator to get rid of that heat. The transmission develops its heat at a much slower rate, so it doesn't need as much surface area to dissipate it.

You're in an area not of my expertise, but I can share some of what I learned at Chrysler training classes and from looking over the shoulders of our resident transmission specialist. If you find debris inside, you would have had a lot of warning that something was wrong. There would have been chattering, vibrations, or abnormal noises. One problem they had that was too common was the small bolted-in pin in the differential would shear off, then the large 1"-diameter pin could slide out. That large pin would catch on the housing and could crack the transmission's case. Often you'd find a large tear in the differential cover and the pin would be poking out. That would lock up the transmission and either you could not move the vehicle by hand, or you'd hear horrendous clunking as it moved a short distance.

The place to start is by measuring pressures at the various test ports. If line pressure is missing, nothing else will work. The torque converter drives the front fluid pump to develop the pressure that moves the valves and engages the clutch packs. While not real common, I have seen more than one time where all the bolts between the flex plate and torque converter fell out. That usually starts out with a banging noise and the transmission works fine. Your ring gear for the starter is on the flex plate, so if the bolts fell out, you would still be able to crank the engine.

A problem I ran into multiple times started out as a shimmy in the steering wheel, and progressed to a small transmission fluid leak. The internal spring in the inner CV joint would break. That is all that pushes the joint's housing into the transmission and keeps it there. I suspect it is possible for the housing to work out far enough that the splined shaft disengages. At that point neither front wheel will rotate, but you might feel a very subtle clunk when changing between "drive" and "reverse". You'll also hear a buzzing noise when trying to engage "park".