The Chrysler 42LE automatic transmission (transaxle)
This transmission was created for the LH large cars launched in 1993. In general design, it is identical to the 41TE automatic transmission, having four forward speeds, learning capabilities, and electronic controls.
Importance and problems of the 42LE and its predecessor
The A604 (predecessor of the 42LE) 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 – also 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.
Although Chrysler released ATF+3 for this transmission, many mechanics and even some dealers continued to use Dexron 2, destroying transmissions. The situation was not helped by mentions that Dexron could be used if ATF+3 was not available. [Also see Chris Theodore’s “Fixing the Ultradrive.”] This continued to be a problem for many years.
42LE development and technical information
Rather than using the cutting-edge technology of Chrysler’s innovative 41TE, a fully adaptive 4-speed electronic transaxle, LH powertrain engineers needed a new transmission because the LH installation was going to be longitudinal instead of transverse, so the output direction had to be turned.
“We put a lot of effort into that,” recalled Howard B. Padgham, powertrain engineer, who also noted that the 42LE’s significant center-section component detail refinements were designed to cope with the added torque of the 3.5 engine, including upgraded clutch packs and barreled axle shafts. The solenoid pack for the 42LE also is integrated into the transaxle for quieter operation.
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 hypoid set also allows the output shafts to cross the input shafts, thus making the lengthwise mounting of the transaxle possible.
The 42LE’s torque converter is the same size employed in the 41TE, but is unique with the cover and longer input shaft.
As an added benefit gained from turning the LH powertrain to a longitudinal mount, the transaxle does not protrude into the front, left wheel well as it does on many transverse-mounted units. This gave the LH’s a much tighter turning radius than most front-wheel drive mid-size sedans.
The 42LE transaxle was assembled at Chrysler’s Kokomo (Ind.) transmission plant, where nearly all of the company’s automatics are built.
The first 1,000 LH sedans off the production line at Chrysler’s Bramalea, Ontario, assembly plant after the June 1992 launch went to rental fleet service. The majority went to Orlando, Florida, with the remainder headed for the Denver, Colorado, area. LH powertrain engineers and technicians were also distributed around Dodge, Chrysler/Plymouth and Jeep/Eagle dealerships at the launch. “It’s part of our commitment to quality,” explained Mr. Padgham. “If any problems should develop, we’ll have a ‘lock’ on the vehicle itself right at the dealerships. We’re determined to have early diagnosis and feedback from the people who know these powertrains intimately.”
42LE automatic transmission design and construction
The 42LE transaxle has an aluminum cast case and stamped-steel oil pan. The transfer chain cover and rear transaxle mount are both cast aluminum and are one unit. It is mounted lengthwise (North to South) in the vehicle.
The 42LE’s torque converter is also the same in design and operating characteristic as other Chrysler torque converters that use clutch pistons. When the clutch is engaged, fuel economy improves, engine noise is reduced, and the transaxle’s operating temperature is also reduced.
Two fluids and oil sumps are used – the transaxle assembly oil pan and differential sump. The two fluids are separated with a weep hole between two seals on the transfer shaft.
Five valves are used in the valve body, and there is no governor or throttle pressure to control the valve body; it was replaced with electrical signals from the output speed sensor and throttle position sensors. Shift valves are also non-existent as they were replaced with solenoids in the solenoid assembly.
The manual valve lever position sensor (MVLPS) and solenoid assembly are attached on the valve body and are submerged in transaxle fluid, which eliminates the need for a sound shield. Noise level and the possibility of contamination from environmental factors are both reduced. Also, some of the solenoids directly control clutch application; clutches are usually indirectly controlled by the solenoids through hydraulic valves. The MVLPS also operates the back-up lights and starter relay, eliminating the need for a back-up relay, PRNDL, and neutral safety switches.
This transaxle also uses a crescent-type gear pump, in which the inner gear is driven by the torque converter impeller hub.
Inside the 42LE are five hydraulically applied clutches. Four of the clutches are released with belleville springs while the other is released with a coil spring. Three are input clutches, giving input power to the planetary geartrain; the other two are holding clutches and hold planetary geartrain components.
- The underdrive clutch is in front of the input clutch retainer.
- The overdrive clutch is the center clutch in the clutch assembly.
- 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.
- The 2-4 clutch is behind the input clutch assembly.
- The low/reverse clutch is in the back of the transaxle case behind the 2-4 clutch.
There are three clutches in the input clutch assembly. The 2-4 and low/reverse clutches share the same reaction plate and are holding elements, which means there are no bands.
Within the 2-4 and low/reverse clutch assemblies, and behind the input clutch assembly, is the planetary geartrain. Inside, there is the front sun gear (in the center of the front carrier and welded to the center of two hubs); the front carrier assembly and rear annulus, which are splined together to be one unit; the rear sun gear (in the center of the rear carrier assembly); and the rear carrier assembly, which includes the rear planetary carrier, front annulus gear, and output shaft as one unit. The rear carrier assembly also has no clutches connected to it as is where all output power passes through.
The 42LE also uses a unique transfer chain with two sprockets that transfer power from the output to transfer shafts; there are no transfer gears. Chain vibrations are minimized with a snubber. The transfer shaft has 33 teeth while the output shaft has 32.
Located behind the battery on the left fender is the transaxle control module (TCM) with a 60-way sealed electrical connection. Basically acting as the “brains” of the transaxle, it determines how the transaxle functions based on information gathered from inputs; it also learns the transaxle’s characteristics to optimize shift quality.
(wired to TCM)
(sent across bus; communication between TCM and other electronic components)
(wired to TCM)
(sent across bus)
There is no vehicle speed sensor on the 42LE; the output speed sensor (on the front of the transaxle case near the transfer chain cover) provides vehicle speed to the body control module (BCM) to cut manufacturing time and costs, while increasing reliability and speedometer accuracy.
The electronic automatic transaxle (EATX) relay controls the default/“limp-in” modes, in which only second, neutral, reverse, and park gears can be used. “Limp-in” mode occurs when a problem is detected, and it protects the transaxle from potentally hazardous operation. Reverse gear is always blocked if the TCM detects the speed is greater than 8 mph, preventing potentially damaging situations.