The Chrysler 41TE, 40TES, and 41TES automatic transmissions (transaxle)
Introduction by Bob Sheaves
The A-604 (“UltraDrive”) automatic transmission was the start of a new generation of automatic transmissions. It was the first electronically shifted hydraulic automatic transmission that used "fuzzy" logic to learn the driver's habits and to learn to adapt its shifting pattern to match the expected driver "request" (meaning the computer learned to vary the harshness and speed of the shifts to adapt to the driver, instead of the driver learning to adapt to the transmission shift points).
No other manufacturer had ever attempted to replace the shuttle valves and servos in their transmissions with electric solenoids under computer control — designing the transmission so that a limp home mode was still intact if the transmission controls failed. The transmissions do not have a valve body, technically, since the solenoids control the flow of transmission fluid directly.
The 4xTE and 4xLE transmissions were similar in concept and basic design to the A-604, with numerous improvements and changes for reliability and to adapt them to particular cars or engines.
This transmission was used on a number of vehicles, but information in this section was taken from the 1995 Sebring Coupe/Avenger introduction materials; the cars were made by Mitsubishi, using Chrysler automatics. The 41TE joined the Neon in 2002, with a gear ratio adjustment in 2003.
The 41TE automatic transaxle was designed and built by Chrysler; the transaxle was an electronically controlled four-speed automatic transmission coupled to a transfer shaft and a helical-geared final drive unit.
The adaptive control system sensed input and output speed changes as shifts occured, and adjusted hydraulic pressure accordingly, to make smoother shifts and make the power train feel responsive without harshness. The system compensated for changes in engine torque or friction element characteristics to provide smooth shifts for the life of the transmission.
The TCM (transmission control module or “transmission computer”) used as ambient and transmission temperature, engine loading changes (caused by climbing grades), loss of engine power at high altitude (due to lower air density), and cruise control to decide when shifts should occur. On up-grades, "anti-cycling" logic prevented was to avoid “hunting.” After downshifting to Third, the TCM only allows an up shift if there is enough torque to maintain the grade in Fourth. When speed control is engaged, downshifts on up-grades occur earlier, to assure that speed is maintained.
During a shift, the transaxle could modulate hydraulic pressure 143 times per second - 14 adjustments in the time it takes to blink (approximately 0.1 seconds) - to assure smooth operation.
Overdrive (Fourth gear) could be avoided by pressing a button on the side of the shifter, which also lit the O/D OFF light in the gauge cluster is illuminated. With overdrive off, upshifts to Third gear occurred at the same speed as in overdrive.
The 9.5 in. (241 mm) three-element torque converter had a 2.65 stall torque ratio. An electronically modulated converter clutch (EMCC) reduced converter slippage; the system raised fuel economy by up to 3%, and isolated the driveline and passengers from engine power pulses, thereby avoiding noise and vibration. EMCC also improved transmission durability by reducing transmission fluid and engine coolant temperatures. On grades, EMCC could be active in Second gear, as well as Third and Fourth gears, because some grades require the use of a lower gear to maintain speed.
Slippage was controlled by partially or fully engaging the converter clutch during steady-speed driving in Third or Fourth gears. Uncontrolled, converter slippage at cruising speeds was about 250 rpm; during partial engagement, slippage was held at about 60 rpm by modulating the hydraulic pressure that applies the converter clutch. Partial engagement always preceded full engagement to make the transition smooth. EMCC disengaged immediately when acceleration was needed.
The transmission only had clutches for gear changes, with no bands. The cast aluminum case cut noise and vibration, and was made stiffer by ribbing developed with computer finite element models.
A transmission fluid temperature calculation system kept shift quality by adjusting transaxle shifting action while cold, increasing durability by calling for EMCC action at high temperatures that might not be otherwise indicated.
Heat added to the fluid by the torque converter, converter clutch, and emanating from pump and gear train parasitic losses, as well as heat removed by the cooler and from the exterior of the transaxle are each computed. Ambient temperature, which significantly affects cooling, is measured or calculated. Also included is a calculation for fluid and air temperatures at start-up.
The transaxle was programmed just before the car was driven off the assembly line, measuring and storing in “fill volume” information unique to each transaxle (the amount of transmission fluid required to fill each actuating element during shifting). This prevented random fill volume variation from causing poor shifts when the transaxle was new.
Instead of using a separate speed sensor, the transaxle’s output shaft speed signal is converted by the transmission computer into a speed signal, used for the speedometer, odometer, and engine controller; that simplifies wiring and making the speedometer and odometer highly accurate and more reliable. The setup can adjust for variations in gearing and tires — dealers can change the constant in the system memory.
The transaxle has a molded shifter with a top-mounted push button to operate the shift gate; roller detents correspond to transaxle lever detents. Rubber isolators for the selector cable housing at both the transaxle and the shifter cut vibration. The shifter includes a cable operated mechanism to lock the steering column and prevent removal of the ignition key with the transaxle in any but the Park position. A cable-operated mechanism prevents the lever from being moved out of Park unless the brake pedal is pressed.
Changes for 1995
An automatic speed control overspeed reduction feature was added to the transmission control software. It helps maintain vehicle speed at the selected set point when descending a grade. The TCM (transmission control module) first senses that the speed control is set. If the set speed is exceeded by more than 4 mph (6.5 km/hr) and the throttle is closed, the TCM causes the transaxle to downshift to Third gear. Subsequent to the downshift, the automatic speed control continues its normal operation. To assure that an upshift is appropriate after the set speed is reached, the TCM waits until the throttle is opened at least 8 degrees by the speed control system before upshifting to Overdrive again. If the driver applies the brakes, canceling automatic speed control operation with the transaxle still in Third gear, the TCM maintains this gear until the driver opens the throttle at least 8 degrees to avoid an inappropriate upshift. The upshift is also delayed for 0.5 seconds after reaching the 8 degree throttle opening in anticipation that the driver might open the throttle enough to require Third gear, thus avoiding unnecessary and disturbing cycling of the transmission. If the automatic speed control RESUME feature is used after braking, the upshift is delayed until the set speed is achieved to reduce cycling and provide better response.
Software changes provided smoother 2-1 low speed, heavy throttle downshifts and kick-down shifts after a coast- down in Third.
In 1996, internal mechanical refinements increased durability; and a newer shift torque management replaced the rudimentary spark advance-based system that was introduced on minivans in 1994. The new system used a selective fuel shutoff to cut engine torque by 50% and reduce energy dissipation during shifts by 30%.
The 40TES and 41TES automatic transmissions
Both the 40TES and 41TES had variable line-fluid pressure (VLP), frequently adjusting internal fluid pressure to reduce parasitic losses, increasing gas mileage, and lengthening the transmission lifespan. Like the 41TE, they had adaptive electronic control and an electronically modulated converter clutch.
As used in the 2007-10 Chrysler Sebring, where they were paired with the 2.4 liter and 2.7 liter engines respectively, the 40TES and 41TES had the following ratios:
|1st||2nd||3rd||4th||Reverse||Final Drive||Overall Top Gear Ratio|
The 41TE has no gasket between the transfer plate and valve body/accumulator housing, the only thing there to provide a seal is a steel separator plate. If you have harsh downshifts and gear engagements, and the more routine maintenance didn't solve the problem, this probably will. You have to catch this quickly.
Since nobody wants to spend three weeks cutting two gaskets from scratch, I figured I'd try some kind of sealer. RTV would not work. The brush-on gasket maker and high tack will probably be too soft... There is a product called “Indian head shellac” which comes in a little brown bottle, it has a cotton ball on a stick inside the cap, which is used to apply it to your workpiece. This stuff is extremely sticky, but it won't get all over the place when you apply it. Put it on the aluminum surfaces that seat on the separator plate, let it dry (it stays soft, like varnish), then slowly torque the bolts down. This will provide a positive seal that will hold up to heat, pressure, and time. I did this to correct harsh kickdowns, and it still works beautifully after three months. I inspected the shellac that was exposed to see how it held up, and it was fine. It won't come off and plug things up, ATF+4 has no solvent effect on it. [Allpar note: we have not tested this.]
Merlin Klotz added:
I've owned 19 Chrysler products and ten have had the 41TE the A604. Until my 2001 Caravan, every one needed a rebuild at around 100,000. They said they had fixed all the problems in 2001, and my 2001 Caravan is now at 230,000 miles and going strong [in fact, there was still a program of continuous improvement after 2001]. At the 200,000 mile checkup and plug change, the shop did the fluids and suggested I replace the solenoid pack. With the new pack, it drove like a new vehicle.
Then, driving my 2004 Stratus (125,000 miles), I suddenly lost power for a few minutes, then regained it; I nursed it home as power came and went. After reading your Web page, I replaced the $114 solenoid pack, filter, and fluid. The solenoid pack screens looked clean; the fluid was darker than expected but did not smell burnt. The filter looked dirty. I used the siphon tip and did the whole job with only a couple of drops spilling; it was a three-hour job except for one nasty bolt. I got it back together, ran through the gears several times, let it idle for 5 minutes, and then around the block. No slip; it was fine. I can only conclude dirt or some wrong fluid gummed up the solenoid pack and perhaps plugged the filter to where I didn't have enough flow.