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41TE, 42LE, A-604, and more: Mopar four-speed automatics based on the Ultradrive

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Chrysler Corporation used three families of four-speed automatic transmissions:

Ultradrive four-speed automatic transmission (Chrysler, 1989)

The Ultradrive was created specifically to be controlled by a computer; it jettisoned bands for solenoids which could activate clutches without clutch valves. It was the first transaxle in the world with completely electronic control, and was revolutionary but poorly tested when launched on the 1989 models.

Automatic transmissions for cars and minivans: A-604 / Ultradrive

The “Ultradrive” (officially coded A-604) had been in development for years, waiting for materials and computers to catch up to the designers’ vision, when it was launched in 1989. Even so, it was not fully tested when the first automatics were bolted into high-end cars and minivans. Chances are few outside of Consumer Reports would have really noticed the problems if it had been restricted to cars in its first few years, but it was put into minivans from the start. A transmission that works reasonably well in cars—and it was still somewhat problematic there—was a far bigger problem in minivans, which were heavier than cars—and were often packed with seven or eight people and their baggage.

The Ultradrive directly controlled clutches with pulse-width modulated solenoids, which made a loud and distinctive ratcheting noise as they worked. The direct action made the valve body much simpler, and eliminated clutch valves, sprags, and roller clutches. Five clutch packs handled all the ratios (Low/Reverse, Underdrive, Overdrive, 2/4, and Reverse); the actual gears were the usual Simpson planetary design, with hydraulically applied clutches.

A-604 Ultradrive planetary gearset

The computer directly controlled shifting, so each shift was made based on engine data, velocity, and the gas pedal position. Even the 1989 Ultradrives adapted for personal driving style and mechanical or fluid wear. A preprogrammed “limp home”  mode allowed driving in first, second, and reverse if certain sensors failed, preventing greater damage and making sure the owner took the vehicle in for repair, instead of driving around with the Check Engine light on. (Some other manufacturers would make it impossible to start the vehicles in this case.)

The Ultradrive was smaller, lighter, and simpler than competing four-speed automatics—and had better performance. It should have been a home run. Famed Chrysler and Ford project leader (known for aluminum Prowlers and F-150s and the Ford GT) Chris Theodore said, “It was a great idea. It was clutch-to-clutch shifting. No under and over clutches, fewer parts, electronic control, but the prior VP of engineering had decided to bet the farm, and they put it into all the Chrysler models at once. Usually when you start out with new technology you want to get a little field experience and make sure all the bugs are out.”

There was pressure on the executives, to be fair; other companies had minivans with four-speed automatics and bigger engines. Still, nobody wanted a minivan that might have a transmission replacement two months after it was built.

1989 Chrysler four-speed automatic

Chris Theodore said, “We had a good team of engineers, but there were just literally hundreds and hundreds of bugs. We just started banging away and banging away cutting them down and knocking them down one at a time.” Issues came from engineering, suppliers, and manufacturing. Week by week, they were eliminated.

One issue was the transmission fluid. Dexron II was not slippery enough and was too thick when cold; other properties were also wrong for the new automatics. Chrysler used its own fluid, ATF+3, but kept telling customers they could use Dexron if ATF+3 was not available. Dealers and mechanics and owners seem to have assumed this meant ATF+3 was basically a money grab; one transmission repair shop told me that they were about to give up on the transmissions when, in 1999, reading a story on Allpar, they decided to try using ATF+3. Their repair rate immediately dropped to normal. A single quart of Dexron could cause serious problems. Eventually, ATF+3 was replaced by ATF+4; and Chrysler stopped writing that Dexron was acceptable.

All these transmissions were made at the Kokomo (Indiana) complex. The later 62TE was based on the same design, but had two more forward gears.

“Not Ultradrives”—40TE, 41TE, 42LE, and 42RLE

The 41TE was essentially an A-604 with a new code.

The new 42LE was derived from the 41TE to support a new set of large cars, using front wheel drive with longitudinal (north-south) mounted engines. The “LH cars”  used a revised version of the 41TE (originally A-606) which could also handle more torque, since the top LH engine put out 214 horsepower—well above the company’s highest output V6 before that time. The transmission variant was coded 42LE—four gears, second torque rating, longitudinal mount, electronic controls.

Chrysler transmission naming convention

The 42LE’s “beefing up” were mainly in the final drive unit. It had higher capacity center-section components, upgraded clutch packs, and barreled axle shafts; to quiet down the characteristic rattling when changing gears, they integrated the solenoid pack into the transaxle, though that made service a bit harder. The torque converter had a longer input shaft.

The 42LE did not replace the 41TE, which was used for many years afterwards; indeed, the 41TE was added to the Neon in 2002.

  R 1 2 3 4
Gearing 2.21 2.84 1.57 1.00 0.69

The 42RLE was essentially the 42RE but adapted for rear wheel drive use (that’s the “R” in the title). The basic changes were obvious—taking out the differential and transfer chain, and resizing the case. The first and second gear ratios were also changed slightly. The transmission was developed originally for the 2003 Jeep Liberty, Jeep Wrangler, and Dodge Ram V6; but it ended up in nearly every rear wheel drive car the company made for a while, including the 2009 Dodge Challenger (V6), the Dakota, and the Durango. The 42LE had a transfer chain to move power to the transfer shafts, eliminating the transfer gears; and it combined the transfer chain cover and rear transaxle cover into a single unit.

Other variants

The 40TE, starting in the 2003 model year, was a lighter version of the 41TE, with the same gear ratios; it was also reputedly cheaper. It debuted in the PT Cruiser, Sebring, Stratus, Neon, and, oddly, given its weight, the Caravan. Choosing too low a torque capacity may have resulted in more transmission failures, particularly on the PT Cruiser and Caravan.

The 41AE, usually referred to as a 41TE despite the different designation, was used for all wheel drive minivans and Pacificas from 1991 to 2008 (minivan use ended in 2004 but the Pacifica crossover, based on minivans, ran from 2004-08).

cutaway view - 1989 Ultradrive

The TES versions (40TES, 41TES) of the 41TE and 40TE were smaller, so they could fit into the 2007-10 Chrysler Sebring. The main changes are making the bell housing and torque converter smaller. The 40TES, having a low torque rating, was used with four-cylinders; the 41TES with six-cylinders. The “TES”  transmissions used variable line pressure (see below), which required a pressure sensor and line pressure solenoid to be added to the valve body. They were used on the Sebring (later renamed 200), the Avenger, and the Journey.

Transmission computer

The computer had direct inputs from the battery, ignition (run), cranking, throttle position, engine speed, turbine speed, output speed, low/reverse pressure switch, 2-4 pressure switch, overdrive pressure switch, and manual valve lever position sensor. It also took information from a bus: target idle speed, coolant and ambient temperature, brake position, engine speed, cruise control status, manifold pressure, and engine/body identifiers. Once it was done with its calculations, it sent information to the PRNDL (which was digital, not mechanical), the transaxle relay, solenoid pack, speedometer, and, with the 3.5 engine, engine torque management system. It also output error messages to the DRBII. The computer limited reverse speed to 8 mph, and controlled the “limp mode.”

A-604 transmission computer 

The system estimated transmission fluid temperature and adjusted shifting when it was cold, and increasing torque converter lockup when it was hot. The system estimated heat added by the torque converter and parasitic losses, subtracting heat removed by the fluid cooler and ordinary radiation. At the factory, the transaxle computer measured and stored the amount of fluid needed to fill each element during shifts, to prevent random variation in volume from causing poor shifts.

Because they adapt to driving style, they can act a little confused when moving from one driver to another. Once the training period is over, they adapt to the driver’s desires. Cars shared by two people with different driving styles can be problematic in terms of odd shifting; Chrysler never linked transmission profiles to driver memory in cars that had it.

In 1995, the transaxle could modulate hydraulic pressure 143 times per second during a shift—making 14 adjustments in the time it takes to blink. The software on the transmissions could be upgraded with a “flash” using dealer equipment; numerous such “flashes” were issued over the years.

Lockup torque converters

All the Ultradrive-style automatics had lockup torque converters, but what is a lockup torque converter?

In a normal torque converter, a sort of fan spins thick oil around. A second sort of fan, connected to the axle, picks up the spin from the movement of the oil. This is done largely because it lets the transmission move at a different speed from the engine—so when the car is stopped, the engine can idle while the transmission is not moving. (If the car sits like that for a long time, the fluid gets quite hot, because it's being stirred on one side while the other side does not move, causing a great deal of friction. That's why it's best to shift into Park, which lets the transmission gears spin around, when idling for more than a few minutes.)

lockup torque converter

The fluid link is much smoother than a direct connection, but has a problem: when the engine and transmission are both moving, some power is lost through the fluid. The connection between the powered fan and the unpowered fan is not 100%. The solution is to have a mechanical link to bind the engine to the transmission when possible, instead of sending power through the fluid. Chrysler originally used a fluid-controlled clutch to do this, locking up only in third gear, and under certain conditions. The Ultradrive, as one might expect, used a computer-controlled clutch. The original UltraDrive (A-604) and 41TE automatics allowed the lockup in third and fourth gear, between 27 mph and 50 mph, under various conditions; in some cases second gear could lock up, too. What’s more, the computer could bind the clutch more gradually if needed. The mechanical connection was released when the driver coasted (no throttle) or when gears were changed. It could feel like another shift, confusing drivers who were counting gears. In any case, the lockup converter could raise economy by up to 3%.

Four-speed automatics: Changes over time

The ATF+3 transmission fluid was replaced in the 1999 model year by ATF+4. This allowed the transmissions to get a “fill for life,”  thanks to the synthetic-base fluid’s superior resistance to heat damage.

Even after the crisis of 1989-91 passed, engineers kept changing the four-speed transmissions to increase durability, comfort, and efficiency, and to cut noise; their efforts never ceased.

In 1994, to extend the life of the transmissions in minivans—both their toughest application and possibly their most important—engineers started cutting engine output during shifts, calling it “torque management.” Before shifting, the transmission computer would tell the body computer, which changed the spark advance to reduce output. The system worked; a more elegant solution, cutting fuel delivery, took its place in 1996. That could cut engine torque by 50% during the shift.

The transmission was called into play for overspeed reduction, part of cruise control. If the transmission was in overdrive (fourth) and the speed was more than 4 mph over the set point with a closed throttle (foot off the gas pedal), the computer downshifted the transaxle to third, and waited until the cruise controller opened the throttle by at least 8° before upshifting again. If the driver cancelled the cruise control, the transmission would still keep the lower gear until half a second after the driver opened the throttle by 8°, in case the driver needed more power.

During the 1997 model year, fluoroelestomer seals were phased in; these were more durable than the original material. The pump housing seal was switched to Polyacrylate on March 14, 1996. The pump’s face and outer tip clearances were reduced in November 1998 to stop delayed engagement issues, which had caused “code 35” to be set.

The valve body gained a reverse-vent reservoir check valve to reduce overdrive clutch wear in 1999. The rear annulus gear was upgraded on February 19, 1997. The splines on the front carrier were induction heat-treated starting around 1999 (this may cause the front carrier to look “heat damaged”). The rear carrier was upgraded to a five pinion design, and the front sun gear had a stronger weld. A new overdrive shaft and reaction shaft support were upgraded for durability.

Transmission range sensors were revised in late 1998 for reliability; because they had a larger connector body, the case had to be changed, and replacing earlier sensors may require a special seal. The new connector also switched from pins to blades.

In 1999-2000, a new solenoid/pressure switch assembly with fewer internal parts was phased in; it was quiet enough to eliminate a sound shield. Input and output sensors were also upgraded because some customers had open circuit error codes. V6 minivans also gained an upgraded, two-piece differential for better strength and lubrication.

Variable line pressure (VLP) was phased in starting in 2006, reaching all transmissions in model-year 2007. The first transmissions to get VLP were coupled to the 3.7 liter V6 (trucks and SUVs) and the LX cars’  2.7 liter V6. Variable line pressure means that the transmission adjusts its internal fluid pressure, cutting parasitic losses from the pump and hydraulic system. That increases gas mileage and improves durability.

Technical transmission talk

Transmissions had an identification label; the first letter was K (Kokomo), followed by the last three digits of the part number; the build date (four digits, based on a 10,000 day internal calendar, so 3843 would be the 3843rd day of production), and the build sequence number.

The transmissions used cast aluminum cases and stamped steel oil pans, and had clutch pistons activating the torque converters. They had separate sumps for the transaxle and differential. Valve bodies used five valves, with no governor or throttle pressure; as stated earlier, shift valves were replaced by solenoids. A manual valve lever position sensor, attached to the valve body and submerged in fluids to eliminate a noise shield, operated the reverse lights and starter relay, eliminating three switches.

42LE automatic

As for the clutches, according to Chrysler:

    1. The underdrive clutch is in front of the input clutch retainer.
    2. The overdrive clutch is the center clutch in the clutch assembly.
    3. The reverse clutch is in the back of the input clutch assembly and uses the same piston, pressure plate, and belleville spring as the overdrive clutch.
    4. The 2-4 clutch is behind the input clutch assembly.
    5. The low/reverse clutch is in the back of the transaxle case behind the 2-4 clutch.

The 2-4 and low/reverse clutches share a reaction plate. The planetary gears are within these clutch assemblies and behind the input clutch; the front sun gear is welded to the center of two hubs. The rear sun gear is in the center of the rear carrier, and the front sun gear is in the center of the front carrier. The rear carrier assembly includes the rear planetary carrier, front annulus gear, and output shaft. The transfer shaft had 33 teeth; the output shaft had 32 teeth. The transmission computer was behind the battery on the left fender.

The torque converter had three elements and a 2.65 stall torque ratio; the converter clutch was computer controlled.

Cars with these transmissions used an output speed sensor (rather than a direct speed sensor), with the body computer calculating actual speed, saving parts and increasing accuracy. The body computer could be reprogrammed by dealers to compensate for changes in wheels and tires.

The shifter had roller detents corresponding to transaxle lever detents, and rubber isolators at the transaxle and the shifter to cut vibration. A cable mechanism locked the steering column and ignition key when not in Park; another cable kept the lever in Park unless the brake pedal was pressed.

Repairs and issues

For years, the transmissions had no gasket between the transfer plate and valve body/accumulator housing; they were sealed by a steel separator plate instead. This could cause harsh downshifts and gear engagements if there was a leak. RTV does not work as a sealant in this application; “Indian head shellac,” according to one report at Allpar, does. Allpar noted they had not tested this, and we have not, either.

solenoid assembly and screen filter

The most commonly needed repair is a fluid replacement, with ATF+4 (which replaces ATF+3).

While the transmissions were not meant to be repaired by end users, and the solenoid packs are not meant to be cleaned or rebuilt by amateurs, a skilled amateur can in fact solve many problems by cleaning and rebuilding the solenoid packs and screen filters; Allpar has details.

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