Mopar Automatic Transmissions

By SRT-Tom · Feb 14, 2019 ·
  1. SRT-Tom
    Modern automatic transmissions can trace their origins to a gearbox that was developed in 1904 by the Sturtevant brothers. This unit had two forward speeds, the ratio change being brought about by flyweights that were driven by the engine. At higher engine speeds, high gear was engaged. As the vehicle slowed down and engine rpm decreased, the gearbox would shift back to low.


    One of the key developments in arriving at an automatic transmission was the use of planetary transmission in the vehicle's gearbox. Probably the first use of which was in the Wilson-Pilcher made between 1900 and 1907.


    In 1934, both REO and General Motors developed semi-automatic transmissions that were less difficult to operate than a fully manual unit. These designs, however, continued to use a clutch to engage the engine with the transmission.


    Parallel to the development in the 1930s of an automatically shifting gearbox was Chrysler’s work on adapting the fluid coupling to automotive use. Invented early in the 20th century, the fluid coupling was the answer to the question of how to avoid stalling the engine when the vehicle was stopped with the transmission in gear. Chrysler itself never used the fluid coupling with any of its automatic transmissions, but did use it in conjunction with a hybrid manual transmission called "Fluid Drive." These developments in automatic gearbox and fluid coupling technology eventually culminated in the introduction in 1939 of the General Motors Hydra-matic- the world's first mass-produced automatic transmission.


    The first torque converter automatic, Buick’s Dynaflow, was introduced for the 1948 model year. Chrysler was late in developing its own true automatic, introducing the two-speed torque converter Powerflite in 1953, and the famous three-speed Torqueflite in 1956. From this time through the 1990s, Chrysler produced seven variations for car and truck use- the A488, 500, 518, 727, 094, 998 and 999. For performance enthusiasts, with larger engines, the A727 was the transmission to have, with its tough,“bullet-proof” construction.


    By the late 1960s, most of the fluid-coupling four-speed and two-speed transmissions had disappeared in favor of three-speed units with torque converters. By the early 1980s, these were being supplemented and eventually replaced by overdrive-equipped transmissions providing four or more forward speeds. Many transmissions also adopted the lock-up torque converter (a mechanical clutch locking the torque converter pump and turbine together to eliminate slip at cruising speed) to improve fuel economy.



    As computerized engine control units (ECUs) became more capable, much of the logic built into the transmission's valve body was off-loaded to the ECU. Some manufacturers use a separate computer dedicated to the transmission called a transmission control unit (TCU), which shares information with the engine management computer. In this case, solenoids are turned on and off by the computer control shift patterns and gear ratios, rather than the spring-loaded valves in the valve body. This allows for more precise control of shift points, shift quality, lower shift times, and (on some newer cars) semi-automatic control, where the driver tells the computer when to shift. The result is an impressive combination of efficiency and smoothness. Some computers, like the one on the Challenger, even identify the driver's style and adapt to best suit it.


    When the 2008 Challenger SRT was produced, it came with the NAG1- a Mercedes 5-speed automatic transmission, that was first used in the 2005 Chrysler 300 and Dodge Magnum. It’s not exactly clear why the switch was made, but the electronic controls probably played a factor.


    NAG1 refers to a category of automatic transmissions that features a round 13-way connector located near the right side, front corner of the transmission oil pad. The “N” stands for “New”, the “A” stands for “Automatic”, and the “G” stands for “Gearbox”. The number “1” represents the generation, which in this case is generation 1. Sometimes, you will notice that NAG1 transmissions will be referenced by other names, such as WA580 or W5A580. These “marketing” names can be interpreted in the following manner:
    • W = A transmission using a hydraulic torque converter.
    • 5 = 5 forward gears.
    • A = Automatic transmission.
    • 580 = Maximum input torque capacity, rated in Newton meters.
    The NAG1 transmission features an electronically controlled 5-speed transmission system with a lock-up clutch that is located in the torque converter. NAG1 gears are activated hydraulically using the electronic controls. The automatic transmission is found in many FCA/Chrysler products, including Dodge Challengers, Dodge Chargers, Grand Cherokees, Dodge Caravans, Ram trucks, and Jeep Wranglers.

    The benefits of NAG1 transmissions include:
    • Increased gas mileage.
    • Increased shift control.
    • Increased service life.
    • Lowered maintenance costs.
    • Improved step-ups through the five gears.
    Though there were some complaints earlier in the transmission’s lifespan (e.g., sensitive to fluid quality, transmission filler tube o-ring leaking and slow shifting), these issues were worked out. In fact, the NAG1 has been praised for its fast shifting capabilities.

    In 2012, Fiat decided to use a new eight-speed transmission with the Pentastar V6 engine. It was adopted, three years later for all 2015 models, with the Hemi engine, including the Challenger.

    The state-of-the-art transmission is a ZF design. The unit is also used by Porsche, BMW, and other high-end car makers. It is designated 8HP45 or 8HP90 when made by ZF. The Chrysler version of 8HP45 is called 845RE.


    The advantages of the transmission are as follows:
    • Wide range of gears. Combines aggressive gear ratios for the lower gears to bolster torque multiplication and low end acceleration, while also providing fuel economy friendly higher gears to improve mileage when cruising on the open road.
    • 98% efficiency in any gear, with an unusually fast locking torque converter.
    • Seamless shifts that take place faster than a person can sense them.
    · Efficient, low-mass triple-line torque converter’s lower inertia helps during shifting and starting, while its twin torsional damper system allows fast engagement with little “slip.”

    · Hydrodynamically cooled clutch, low-viscosity transmission fluid, and chain-driven axial parallel vane cell pump.

    · Four planetary gear sets and five gear shift elements (two brakes, three clutches); there are two opened shift elements per gear, minimizing drag losses. Only two shift elements are open in each gear, cutting parasitic losses; and it can make extreme transmission shifts, such as eight-to-second kick down, in one step.

    · Touch-shifter on the console, with manual shift control using steering-wheel-mounted paddle shifters. Provides driver with full control of the upshifts and the transmission only downshifts when necessary to prevent the engine speed from dropping too low.

    The following photos illustrate two semi-automatic shifters that allow drive to manually select driving gears.

    Mopar T-shifter (used with NAG 1)

    Paddle shifters

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