Ford AOD Transmissions

Like an automotive Rodney Dangerfield, the AOD automatic gets no respect, and perhaps not without some justification. Take its decidedly nonperformance-oriented First-Drive-OD shift detent (please!), which makes finding Second gear—while manual shifting—an indirect and indelicate affair involving a slam from First to Drive, and then back down to First. This type of arrangement does not command an enthusiast’s respect, nor does it make for long tranny life. Neither is respect earned by the AOD’s engine-bogging leap from Second to Third, nor the early version’s constant shuffling between Drive and OD.

Then again, at least it has Overdrive—which for any civilized form of street use puts the AOD miles ahead of slush boxes having only a direct-driven top gear. And if someone could engineer fixes to its known shortcomings, the strong-by-design AOD would lend itself to performance applications in a huge array of FoMoCos, ranging from street or race late-model Mustangs to street rods to ’60s musclecars updated for the new century. Enter LenTech Automatics, a firm dedicated to earning the AOD some serious respect. LenTech’s Len Bertrand saw opportunity in the culprit responsible for some of the AOD’s poor reputation—its unique dual input shaft arrangement.

Before going any further, a quick look at an AOD’s stock power input is in order. As delivered in thousands of Fox-bodied Mustangs, older Crown Vics, light-duty pickups and vans, and all manners of pre-electronic, rear-drive Fords, the ubiquitous AOD went without a typical torque converter lockup clutch. Instead, it used a concentric pair of input shafts. The hollow outer input shaft was driven off the torque converter turbine and powered First, Second, and Reverse gears, while the inner shaft took engine rpm directly off the converter front cover—not via the turbine—to engage Third and OD. Thus, First and Second could benefit from the converter’s torque multiplication, while Third and OD were effectively driven straight off the crank, always in lockup—a prime cause of bogging or stumbling on the 2-3 upshift. To be precise, Third gear does receive some power via the converter and the outer shaft, but the brunt is borne by the little flexplate-driven inner shaft.

This small-diameter inner shaft is rightfully viewed as a weak link, not so much in Overdrive—which will never see much track use or even the peaks of the horsepower curve—but more so in Third, where a high-horsepower engine’s full-power upshift from Second can wreak internal havoc.

Ironically, with that three-dimensional visualization that is the hallmark of the mechanically gifted, Bertrand was able to see some potential advantage in this dual input flow. It offered flexibility in the means by which power could be channeled through the AOD’s compound planetary gearset—so named because it uses two sets of spiders mounted on a common planetary carrier instead of two separate carriers. If you’re familiar with the tough, old FMX, then you’ll feel right at home inside an AOD—which shares similar planetary architecture. Bertrand tells us the AOD in stock form can handle up to about 450 hp—with Third gear’s actuation by the small shaft being the limiting factor in an otherwise quite strong gearbox. By comparison, LenTech’s range of modified AODs have power-handling capabilities from 600 to 1,200 hp. Most of the increased power-handling capability of LenTech’s various AODs comes from modifying the route taken by engine power to and through the planetary geartrain. In fact, by specific modifications to the valvebody (the hydraulic brain of the tranny responsible for clutch and band operation) and, in one case, the use of a unique converter, LenTech is able to offer four different AOD models that use three distinct powerflows (see sidebar).

We’ll take a more detailed look here at one of the LenTech quartet—the Street Terminator Lockup. This stout and streetable AOD sells for $2,395 and offers lockup (properly, just in Overdrive) for maximum efficiency yet shifts with authority—either manually or automatically. It has a proper 1-2-¾ pattern for manual shifting, and has components and internal power flow modified to deal with up to 700 hp—and up to 800 hp with an optional revised outer input shaft.

Though the model line consists of four transmissions, no two AODs leaving the shop are likely to be identical, as LenTech has a converter, line pressure, and other options that can be tailored to suit most any car-engine combination. Bellhousing patterns are available for small-block and 429/460 applications, and will be for FEs, too, by the time you read this. The company backs all its AODs—street or race—with a rather remarkable full one-year parts and labor warranty, three years on the valvebody, and two on the torque converter. The purchaser is responsible only for shipping in the event of problems. This confidence alone should reap LenTech AODs some much deserved respect.