I have a '93 Dynasty that I bought new when I worked at the dealership. The next time I get it out of storage, it will likely turn 4,000 miles!
Your transmission is in "Limp-in" mode which hydraulically gives you a choice of Park, Reverse, Neutral, and Second gear when any forward gear is selected.
There are three possibilities that cause the system to go into limp-in mode. The most expensive is when the computer detects slippage in one of the clutch packs. On older transmissions, as the clutch plates gradually wear out over time, the shifts get sloppy, or mushy. The change happens gradually and is hard to notice until the slippage is so bad, you have to have the transmission rebuilt. Those transmissions usually give you tens of thousands of miles of warning. Your transmission is the first ever computer-controlled unit. As the clutch plates wear, it takes a larger volume of fluid to completely engage them. To prevent the mushy shifts, the computer monitors the needed ccs of fluid and adjusts the timing of the shift solenoids to overcome this normal wear. By applying third gear, for example, just a little sooner before it releases second gear, the slippage doesn't have time to occur and won't be noticeable by you until the day when the plates are so worn, no amount of fluid can completely apply them. That's why you don't get any warning of the impending failure. One day it still has a nice crisp shift feel, and the next day you have your problem. On newer Chrysler transmissions, the programming that detects this slippage is more forgiving. It should also be noted that when you first start out after starting the engine, it will always start in first gear, like normal, and will upshift properly until it hits the gear where the slippage is occurring. Then it will default to second gear and stay there until you turn the ignition switch back off and restart the engine.
Sometimes you can overcome the slippage by accelerating a little harder than normal, then letting off the gas when the problem shift is about to occur. The lower-than-normal torque will reduce or eliminate the slippage allowing it to fully apply the clutch pack. At that point you can continue to drive like normal until you have to slow down. It's a simple trick that can get you home.
The transmission slippage problem was very common in the early to mid 1990s, but now we're seeing more and more sensor problems which is a relatively inexpensive repair. There is an input speed sensor which monitors crankshaft rpm, and an output speed sensor which monitors half shaft rpm. The gear ratios are programmed into the "Electronic Automatic Transmission Controller, (EATX). This computer knows which gear it has commanded on, and how fast the half shaft should be turning compared the crankshaft speed. Any discrepancy between them is proof of clutch plate slippage. These sensors can not report incorrect speeds. They fail to report any speed. Because of the defect, the computer doesn't know how things are working so it defaults to limp-in mode. Lucky for us, this is now the most common failure of this system. Unlike clutch pack slippage, a sensor defect is usually detected as soon as the engine is started, before the car is even moved or the transmission is shifted out of park. This failure will result in the transmission starting out in second gear right away.
The third possibility is a general failure of the EATX. This is very rare on Chrysler products. Out of 100 cars that are repaired by installing a new computer, 98 will be GM products, one will be a Ford, and the last one will be a Chrysler or import.
To summarize, if it starts out in second gear, suspect a failure of a sensor, the computer, or related wiring. If it starts out in first gear but bangs back to second gear right after a shift, suspect clutch plate slippage or other internal fluid leakage.
Another point of interest is that the first 100 of these transmissions were hand assembled and were bullet proof. At least two in the Chicago area were known to reach more than 130,000 miles without a problem. Later, they had a huge failure rate due to "tolerance buildup" on the automated assembly lines. Every part had a specification and an acceptable tolerance, or how much it could be off and still work fine. If enough parts were off a little and in the same direction, there could be a failure after only a little wear took place. In particular, one problem was where a metal sealing ring would ride on a rotating shaft. If a thrust washer wore a little, the shaft could walk back and forth a little, which was normal, but if the sealing ring was out of position just a little too much, fluid leakage would occur and the clutch wouldn't fully apply. Clutch slippage was the result. Since this transmission was first used in 1989 models, there have been so many modifications and updated parts that the reliability has improved greatly. In the mid 1990s, GM wanted to buy the design from Chrysler, but rather than wait for them to work the bugs out, GM and Ford designed their own computer-controlled transmissions, ... And had all the same problems Chrysler had years earlier.
You should also be aware that anytime the battery is disconnected or run dead, the memory is lost in the EATX. It can take up to two miles or about 12 shift cycles, including getting into overdrive, (4th gear), for the computer to relearn the clutch volume index, (CVI), which is the volume of fluid needed to apply each clutch pack. Until it relearns this, it could shift very harsh or kinda mushy. Most mechanics will take your car on a short test drive to do this relearn procedure so you will never experience the shifting issues and you won't complain or think they did something to damage your car. Other knowledgeable mechanics will at least inform you of the unusual shift feel and reassure you it will go back to normal.
Clutch volume index can be read out on the DRB2 or DRB3, which are Chrysler's hand-held computers used to access data from the car's many computers. To my knowledge, most aftermarket computers can not access this data. Transmission experts can look at these four numbers to get an idea of how much clutch plate wear has already taken place, and how much life you might reasonably expect from the transmission. There will also be diagnostic fault codes in the computer's memory indicating the reason it went into limp-in. Don't disconnect the battery until someone has had the chance to read and record the code(s) in case they don't come back right away. Disconnecting the battery will erase that valuable information. Also, if your car has a remanufactured transmission from Chrysler, they now have a three year warranty, but to be covered under their warranty, they require their mechanics to retrieve this data and include it on the warranty claim. They must also replace the computer and send the old one back to Chrysler with the transmission. There, they can access even more information in the computer, which is not lost when the battery is disconnected. They can prove whether this information was or was not properly retrieved.
Most reputable transmission shops are aware of the many updated parts that are available to rebuild your transmission, but because of the cost for all of them, it can sometimes be less expensive to just have a remanufactured unit installed at the dealership. The last place to go for this type of repair is an independent repair shop that doesn't specialize in transmission work. For them to do a reliable repair, they will likely just take your transmission out and send it to the transmission specialty shop, so now you have two shops involved in the repair, and a higher cost.
I have a '91 Dynasty that I bought because it also has this transmission problem. When I get around to replacing it, I'm going to compare prices for a rebuilt transmission from the dealership and from a local transmission shop, then install it myself. It's kind of involved for most do-it-yourselfers, and Chrysler requires their mechanics to flush the cooler with a cleaning chemical. I thought about rebuilding it myself, but I don't know about all the updated parts, and the cost to replace all of them is considerably more than the cost of a rebuilt unit.
Wednesday, October 21st, 2009 AT 4:08 AM