History
The Ultradrive was a significant technological advancement in transmission operation, one of the first electronically controlled automatics. It pioneered many now-common features such as adaptive shifting, wherein the Electronic control unit optimizes shifting based on the driving style of the operator. It earned a reputation for being unreliable. While the Ultradrive transmission had numerous issues, reportedly due to being rushed into production, a common problem was not necessarily caused by a design flaw, but by poor labelling: both owner's manuals and transmission fluid dipsticks advocated the use of Dexron transmission fluid in the event the required fluid was not available. The transmissions were designed to use a special fluid (Type 7176, also known as ATF+3, now superseded by ATF+4) and many owners reported failures from the use of Dexron, as well as temporary issues which were resolved when the proper fluid was added.
There may also have been mistaken impressions of failure due to the "limp home" feature. When the computer sensed a problem, such as a sensor giving an inappropriate reading, a code would be stored in the car's computer and the transmission would default to second gear only, under transmission computer control, so that owners could still drive to a service location for diagonsis and/or repairs. This could have caused perceptions of failure and premature replacement. A major drawback to the "second gear only limp mode" was, if second gear was the defective gear, the vehicle would not go forward at all.
The torque converter measured 9.5 in (24 cm) in diameter and was mounted to the flywheel by a flexible drive plate. The transaxle was cooled through an oil-to-water heat exchanger in the collector tank on the radiator, and/or a standard oil-to-air heat exchanger. There were no bands or mechanical holding devices; ratios were supplied by five different clutch packs. This allowed the transmission to be lightweight and to use fewer moving parts than the three speed it replaced.
The 41TE transmission which directly replaced the Ultradrive had a similar design and could be considered an evolutionary change, but it included different valve bodies, solenoid packs, sensors, and other components to increase reliability. This line was also given a flash-programmable TCM and, in 2006, a variable line pressure hydraulic system was phased in, which boosted performance and longevity.
Mitsubishi's Sportronic transmission was a modified version of the 41TE.
Read more about this topic: Ultradrive
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