When we began building the Hot Rod Hauler, our updated ’73 Ford F-350, we had a number of objectives. One of the most ambitious was to increase fuel economy while maintaining towing capacity. The first modification toward that goal was the installation of an E4OD overdrive automatic transmission from Gearstar Performance Transmissions.

As we showed last month, replacing the C6 with an E4OD was not without challenges. There were some crossmember modifications required, the gas tank had to be slid back in its mounts, and the front end still required some “massaging” with a rubber mallet. However the biggest challenge was the shift linkage. It could have been done with a cable but we elected to take advantage of our friend and master machinist, Tim Smith, and build a mechanical linkage with a bellcrank.

With the mechanical part of the installation done, it was time to turn our attention to the computer and wiring harness that makes our high-tech trans work. From a functional standpoint the E40D has some unique features. As you would expect, Park, Reverse, and Neutral are standard shifter positions, but unlike many other four-speed overdrive automatics there are only three other shifter positions—D, which allows the transmission to shift through all four gears, D2 which locks the transmission in Second gear only (the vehicle starts in second and stays there), and D1, which locks the transmission in First and keeps it there. What’s missing is a Third gear position, but while it may not be on the gearshift indicator, it is available at the push of a button. Activating the “cancel switch” prevents the transmission from shifting into Fourth (however the converter will still lock).

In stock form the E4OD is controlled by a system referred to as the EEC-IV, it’s a processor that controls both the engine and transmission. What we needed was a stand-alone controller to operate just the transmission and through Gearstar we found just what we needed; the Compushift II from HGM Automotive Electronics, a specialty equipment manufacturer that designs and supplies leading edge electronic systems for automotive aftermarket use. Compushift II operates automatic shifting, paddle shifting, and torque converter clutch lockup for a wide variety of transmissions, including the E4OD.

Installing the computer and wiring harness is simple enough, however we urge you to go against the normal tendency to disregard the instruction manual and dive in. Despite the fact that all the wires are clearly labeled, all the plugs are dedicated and will only fit in the proper place. Improper installation can not only keep the transmission from operating properly, it can damage the control unit. So do yourself and the tech guys at HGM a favor and read the manual before you begin installation.

While we are on the subject of installing the HGM controller, we should touch on what can go wrong and, surprisingly, the most common problem is easy to avoid—poor grounds. After everything in your truck is painted, plated, and powdercoated, it can be tough to find a good spot to ground electrical components, but a good ground is absolutely essential to the proper operation of the HGM system (as well as every other electrical device). That’s why HGM recommends grounding their system directly to the block (but the connection point still needs to be clean, bare metal).

We began our installation by running all the wires to their various locations. The big trick here is to route them out of harm’s way, avoiding things like the exhaust system and sharp edges that can damage wire. With the harness installed, the next chore was to find a place to mount the control unit inside the cab.

The next step was attaching the throttle position sensor to the carburetor. For carbureted engines HGM offers their AccuLink kit to mount a TPS on virtually any carburetor. For those engines that are fuel injected, the existing TPS can be used to supply the transmission computer the necessary signal.