The Chrysler 41TE, 40TES, and 41TES automatic transmissions (transaxle)

Introduction by Bob Sheaves

The A604 was the start of a new generation of automatic transmissions for Chrysler Corporation. 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 and not shuttle valves.

I have heard that Chrysler put on over 3 million miles of testing and durability on the A604 before it was released to the public. Hearsay tells me that this was when the lubricity issues with Dextron 2 was first realized and the ATF+3 was developed. Care was taken to mention this in the owners manuals to show that proper oil must be used to prevent breakdowns. As this was a new oil to the public at the time, it was not available to the corner oil change place. The public thought that ATF was ATF was ATF+3 and they were all the same. Even some dealers were ignorant of this issue of oil type and propagated this myth that started tha ball rolling on the poor public perception of the A604.

40TES and 41TES are after the 41TE.

41TE Automatic Transaxle

(Note: though this transmission was used on a number of vehicles, this information is taken from the 1995 Sebring Coupe/Avenger introduction materials. The 41TE joined the Neon in 2002, with a gear ratio adjustment in 2003.)

The Chrysler-designed and built automatic transaxle consists of an electronically controlled four- speed overdrive transmission with a transfer shaft and a helical-geared final drive unit.

A transmission control module (TCM) provides fully adaptive electronic control of all shifting. Shifts are very smooth because the electronic control senses input and output speed changes as shifts occur and adjusts hydraulic pressure accordingly. Adaptive electronic control provides up shifts and down shifts with a smoothness unattainable with strictly hydraulic transmissions. In so doing, adaptive control makes the power train feel responsive without harshness. These controls inherently compensate for changes in engine torque or friction element characteristics to provide consistently smooth shifts for the life of the transmission.

This image shows the similar 42LE.

The TCM considers operating conditions such 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 engagement of automatic speed control in determining when shifts should occur. On up-grades, "anti-cycling" logic assures that down shifts do not occur cyclically. After a down shift to Third occurs, the TCM determines the torque required to maintain the existing speed and/or acceleration level and only allows an up shift if the same torque level is available in Fourth gear. When speed control is engaged, down shifts on up-grades occur somewhat earlier than with driver control of the throttle to assure that speed is maintained.

Engagement of overdrive (Fourth gear) is controlled by a push button on the side of the shifter. When the switch is in the OFF position, the transaxle will not shift to overdrive and an O/D OFF light in the instrument cluster is illuminated. Having overdrive off makes driving smoother in traffic at low and moderate speeds where overdrive is not needed. With overdrive off, upshifts to Third gear occur at the same speed as in overdrive. Nomenclature is provided on the shifter, showing how the switch operates.

The 9.5 in. (241 mm) three-element torque converter has a 2.65 stall torque ratio. An electronically modulated converter clutch (EMCC) reduces or eliminates converter slippage. EMCC increases EPA fuel economy up to 3% compared to a non-EMCC converter while maintaining smooth operation. EMCC isolates the driveline and passengers from engine power pulses, thus avoiding objectionable noise and vibration. EMCC also improves transmission durability by reducing transmission fluid and engine coolant temperatures when climbing grades. On grades, EMCC may 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 is controlled or eliminated by partially or fully engaging the converter clutch during cruise conditions -- essentially steady speed driving in Third or Fourth gears. Uncontrolled, converter slippage at cruising speeds is about 250 rpm. During partial engagement, slippage is held at about 60 rpm by modulating the hydraulic pressure that applies the converter clutch. Partial engagement always precedes full engagement to make the transition smooth. EMCC disengages immediately when acceleration is needed.

The transmission uses only clutches to change ratios. Clutches provide smooth, consistent shifts whereas bands, which are used in some transmissions, are harder to control and less consistent.

The cast aluminum case reduces noise and vibration due to internal loads through the addition of ribbing that was developed using computer finite element models.

A sophisticated transmission fluid temperature calculation procedure (algorithm) maintains peak shift quality by adjusting transaxle shifting action after cold starts and during warm-up. It also enhances transaxle 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 provides excellent shift quality at time of delivery to the customer due to a programming procedure performed just before a car is driven off the assembly line. The procedure measures and stores in TCM memory "fill volume" information unique to each transaxle. "Fill volume", which is the amount of transmission fluid required to fill each actuating element during shifting, affects the timing of shift actions -- a critical factor in shift quality. This procedure eliminates the possibility that fill volume variation will cause poor shifts when the transaxle is new.

The vehicle speed signal that drives the speedometer and odometer and is used by engine controller is provided by the TCM. This makes the speedometer and odometer highly accurate, eliminates the need for a separate vehicle speed sensor and simplifies the wiring by eliminating two of the three wires the vehicle speed sensor required.

The electronic transaxle supplies an output shaft speed signal the primary purpose of which is to control shift quality. The TCM translates this signal into an output that mimics the signal from a vehicle speed sensor. A correlation factor transforms this signal into a vehicle speed signal by adjusting for variations in gearing and tires. The correlation factor is programmed into the TCM memory.

The automatic transaxle has an easy-to-grip molded shifter with a top- mounted push button to operate the shift gate. The shifter has quiet roller detents that correlate to the transaxle lever detents for consistency and smooth operation. A range indicator is adjacent to the lever. To reduce transmission of vibration to the passenger compartment and shift lever, there are rubber isolators for the selector cable housing at both the transaxle and the shifter. The shifter includes a cable operated mechanism that prevents locking of the steering column and removal of the ignition key with the transaxle in any but the Park position. This prevents the car from rolling unintentionally and deters theft by preventing the drive wheels from rotating because the transmission is held in Park by the ignition lock. To prevent abrupt starting through mistakes in selector lever operation, 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.

1996 addition

The 41TE transaxle available on 1996 minivans is a refinement of the 1995 minivan transaxle. It is the only automatic transaxle with adaptive controls that use real-time feed-back for all shifts available in a minivan.

During a shift, the transaxle can modulate hydraulic pressure 143 times per second - 14 adjustments in the time it takes to blink (approximately 0.1 second) - to assure smooth operation.

The 41TE transaxle is simpler, lighter and more compact than competitive transaxles of similar capacity. Basic features are unchanged from 1995.

Customer requirements regarding the transaxle revolve primarily around proper function. A number of internal mechanical refinements increase the durability of the transaxle in response to greater customer expectations.

Engine torque management is used with 2.4, 3.3 and 3.8-liter engines equipped with the 41TE transaxle to give quicker, smoother shifts than would be possible without this feature. Torque management affects two separate operating conditions: shift torque and stall torque.

Sophisticated shift torque management replaces the rudimentary spark advance-based system that was introduced on minivans in 1994. It improves shift quality and enhances transaxle durability. The new system uses a selective fuel shut off to achieve a 50% reduction in engine output torque and a 30% reduction in energy dissipation during shifts. It requires precise interactive communication between the PCM and TCM for successful completion.

2001: the magic year?

Merlin Klotz wrote:

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. 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.

The 40TES and 41TES automatic transmissions

Different in their torque ratings, the 40TES and 41TES feature variable line-fluid pressure (VLP) within the transmission. The VLP transmission frequently adjusts its internal fluid pressure to reduce parasitic losses from the pump and hydraulic system, increasing gas mileage and lengthening the transmission lifespan.

Like the 41TE, they have adaptive electronic control and an electronically modulated converter clutch.

As used in the 2007 Chrysler Sebring, they are paired with the 2.4 liter and 2.7 liter engines respectively, and have the following ratios:

Gear	Ratio
1st	2.842
2nd	1.57
3rd	1.0
4th	0.69
Reverse	2.21
Final Drive Ratio	3.91
Overall Top Gear	2.70

The gasket

fabinator wrote:

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 seperator plate, let it dry (trust me, 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.

For more fluid and maintenance/repair information, click here.

For a good deal of four-speed automatic repair information, click here.

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