Automatic transmissions have been with us for a long, long time. In fact, the basics can be found in the Model T Ford. At the heart of an automatic transmission are the planetary gearsets. As gears go, planetaries could be considered the most sophisticated. Made up of three elements—a sun gear, ring gear, and planet pinion gears—planetary gear assemblies can provide forward or reverse rotation, a speed increase, constant speed, or a speed reduction (to provide a variety of gear ratios multiple gearsets are used).
In operation, a planetary gearset requires an input (power from the engine), an output (power going out), and a reactor (one of the elements that is held stationary). The gear ratio and the direction of travel depend on which element is performing each function; when none of the elements are held, the transmission is in neutral. To keep the reactors stationary, bands are used to hold the ring gear to the transmission case, clutch plates and one-way roller clutches are used to hold the planetary elements. In the Tin Lizzie, bands were applied mechanically when the driver stepped on a pedal—modern automatic transmissions use hydraulic pressure.
The valvebody is the “brain” of the transmission. It controls shifting by controlling which reactor is applied to what gearset and when. Historically, automatic transmissions used hydraulic pressure from a governor, throttle valve, or vacuum modulator to determine shift points, but today they use computer-controlled electromechanical servos.
While computer controls have improved the performance and efficiency of modern automatic transmissions, without a Transmission Control Unit, or TCU, they're a big, dumb aluminum container full of parts. That means that stuffing one under the floorboards of your custom classic truck has some challenges. But for every problem there is a solution, and in this case it comes from the appropriately named Powertrain Control Solutions.
As the brain trust at PCS explains it, “The primary factor separating the modern electronic automatic transmission from yesterday's hydro-mechanical automatic transmission is the speed and complexity of the logic used for transmission behavior. The hydro-mechanical automatic transmission of yesterday could only make its decisions based on throttle position, engine load, and driveshaft speed. Whereas the TCU can use these inputs as well as torque converter speed, engine speed, wheel speeds, traction control parameters, electronic throttle position, fluid temperature, engine temperature, brake pedal actuation, forward and lateral acceleration, as well as several other parameters. The TCU can also utilize manual shifting operation and provide altered transmission behavior for special conditions (road race, drag race, dynamometer, snow, towing, etc.).” Translated, that means the PCS TCU is definitely OK.
For those looking for a straightforward, easy-to-live-with transmission controller, PCS offers the Simple Shift. Neither a laptop, nor a technician in a lab coat are required to install the Simple Shift and it will completely control shift points, shift firmness, and torque converter lockup. Transmission shift points are adjusted by dials on the end of the control unit and diagnostic capabilities are communicated by flashing LEDs that also indicate what gear the transmission is in and whether or not the torque converter is locked. For those who want more adjustment options, the Simple Shift Tuner is also available. The handheld tuner can remain connected to the Simple Shift or be removed when programming is complete.
Also available from PCS is the TCM-2000. Similar to all their controllers, the TCM-2000 features dual calibrations that allow the driver to pick from two distinctly different transmission operating modes (sport mode, tow-haul mode, etc.), with programmable shift points, shift firmness, and torque converter lockup tailored to each application. Unique to the TCM-2000, it's capable of supporting a wide range of transmissions from GM, Ford, Chrysler, and a variety of imports. A CAN interface (controller area network, which lets multiple computers talk to one another) allows the TCM-2000 to be seamlessly used with CAN-based vehicles or ECUs and also simplifies the connection to a PCS Paddle Shifter or GSM-5000 Gear Select Module.
To put shifting at your fingertips, PCS offers the GSM Push Button Shifter that replaces the shift lever and linkage with a small touch-pad control module and sealed actuator. Thanks to its design the GSM control module can be surface or flush-mounted and is small enough to fit in consoles, dashes, door panels, or even armrests. Each button is recessed to avoid inadvertent touches and brightly backlit for darker environments. An easy-to-read display shows you what gear you're in. Standard control modules utilize a PRND configuration along with plus and minus buttons for shifting up or down.
Another unique shifting option is the PCS Paddle Shifter. Designed to provide the look and feel of an OEM system, it will bring out the Ferrari F-1 driver in anyone—it's that cool. Easily installing behind any aftermarket 5-, 6-, or 9-bolt steering wheel, the Paddle Shifter communicates with the transmission control unit via a wireless receiver module that plugs into the PCS transmission control units wiring harness.