Four-Speed Chrysler Automatic Transmissions

This page has descriptions, development, and a link for repairs

Chrysler used two basic types of four-speed automatics. The first, used primarily in cars and minivans, was originally called the Ultradrive or A-604, and eventually came to use names such as 41TE. The second, used primarily in trucks, was originally designated A500 and A518.

The A-604 / Ultradrive / 4xLE / 4xTE system

Brian Meyer wrote:

Initially called A604 Ultradrive, this transaxle was the first, and for a long time the only, fully electronic transaxle, and it has come a long way from 1989, when every day a new service bulletin came out revising this
part or that procedure...

Now called the 41TE (4 forward ratios, load range 1, transverse mount, electronic), this transaxle still sees duty in minivans and all other Chrysler front-drive transverse applications, like the Pacifica, Stratus/Sebring sedan, etc. (finally replacing the tried and true 31TH, nee A470, in the Neon).

Some definitions are in order -- by fully electronic, I mean that pulse-width-modulated solenoids (remember the ratcheting noise early 604s made?) act directly on the different clutch sets to attain the different ratios. This allows for a simpler valve body assembly, compared to others where solenoids are on/off devices and only act to divert ATF to one shift valve or another. These solenoids are controlled by a dedicated module (TCM) that monitors and adjusts trans ops through several sensors, such as speed sensors on the input and output shafts, as well as monitoring engine data over the data bus.

There are no bands or mechanical holding devices (sprags, roller clutches, etc). All ratios are supplied by five different clutch packs (Low/Rev, Underdrive, Overdrive, 2/4 and Reverse). Compared to other domestic front drive transaxles like Ford's AX4N or GM's 4L40E, the 41TE is lighter, smaller and less mechanically complex while providing improved performance.

Finally, these electronic controls allow the TCM [computer] to monitor the transaxle's performance and adjust solenoid actuation and timing accordingly with the goal of maintaining shift quality throughout the life of the vehicle.

The 41TE also was adapted for use in longitudinal front-drive cars (LH bodies) as the 42LE (originally A606) and as a rear-drive trans to replace the old 30RH (A999) in the Jeep Wrangler... although, at this time I don't know if that made it to production. Principles of 41TE design were incorporated in Chrysler's electronic 45RFE rwd trans (another excellent Chrysler design that can provide up to 8 different ratios depending on TCM programming!).

Through diagnosing and servicing Chryslers, I developed a great appreciation for their ingenuity and elegance of design. .

David Zatz wrote:

The A604 was a revolutionary development, but it suffered from Lee Iaccoca's desire to rush it into production. It was the first electronically shifted hydraulic automatic transmission that used fuzzy logic to learn to adapt its shifting pattern to match the driver's habits and tastes, as well as to compensate for internal conditions. No other automaker had attempted to replace the many valves and servos in a transmission with simple solenoids controlled by a computer. What's more, Chrysler was often not followed by others in their use of a "limp" mode, to take the driver home even in cases of control failure. The limp mode deliberately restricted the driver to second gear so the vehicle would be serviced.

Aside from the electronic control mechanisms, the four-speed automatic is a conventional automatic with hydraulically applied clutches that shift a planetary gear train.

These transmissions take a few days of getting used to a driver, during which they may act confused, but after that, they vary the harshness and speed of shifts to meet the driver's tastes. It almost seems to read the driver's mind. The obvious problem with this is that if you have two different drivers, each with different tastes and habits, the transmission can have a hard time keeping up. (Using two profiles linked to the memory seats was never done.)

Chrysler reportedly put over a million miles of testing on the A604 before its first use in 1989, which is when they discovered that Dexron fluid was not good enough. However, the company did not make this clear to customers, saying that Dexron was good enough if their own fluid, ATF+3, was not available. Nor did they get the word out to oil change places and corner mechanics. As a result, many, many transmissions were destroyed. Even some dealers apparently told customers they could use Dexron. The result was a terrible reputation for quality - we have been told by one transmission rebuilding establishment that the horrific return/repair rate on their own transmissions fell to normal levels when they switched to ATF+3, and that was around ten years after the A-604 was first introduced!

Most of these transmissions are made in Kokomo, Indiana, which is reportedly working on a six-speed evolutionary version to go into the next-generation minivans.

Click here for lots of repair information on this transmission.

The 42LE (LH series): refined A-604 - Chrysler-provided information

Drawing on the cutting-edge technology of Chrysler's innovative 41 TE, fully-adaptive, 4-speed electronic transaxle, LH powertrain engineers still were determined to literally,"do their own thing." First off, because the LH installation was going to be longitudinal instead of transverse, the 42LE output direction had to be turned, and because the superior torque output of the 3.5-liter engine on LH was beyond the 4ITE's design parameters, a stronger final drive unit was required.

The 42LE's significant center-section component detail refinements were designed to cope with the added torque, including upgraded clutch packs and barreled axle shafts. The solenoid pack for the 42LE also is integrated into the transaxle for quieter operation. The 42LE's torque converter is the same size employed in the 4TE, but is unique with the cover and longer input shaft.

In the final drive unit, a hypoid ring and pinion gear set delivers drive to the differential and from there to the drive axles, Precise adjustment of the hypoid gears to assure quiet operation is automated.

The truck transmissions: A500 and A518

These transmissions continued the bulletproof line of the A727, A904, and A999. In essence, they were an A999 transmission (which mixed 904 and 727 specifications) with a lockup torque converter and overdrive planetary gear set.

The gear ratios of these transmissions were not matched to the engines, which hurt gas mileage and perceptions of power though it saved some money. Generally, vehicles should be just above their peak torque while at cruising speed, which is generally around 65-75 mph in North America, to provide a good mix of mileage, hill-climbing, and passing acceleration. However, at the time, the corporation decided that money was not available to do this. The effect may not have been too bad.

We can infer from trade journals' surveys that the warranty costs were roughly the same as the three-speed A904 and A999 transmissions, and only a little more than the legendary A-727.

The 45RFE transmission

Click here for other transmissions - click here for engines

---

---