For this year’s car we chose Gearstar Performance Transmissions’ Ford AOD Level IV automatic overdrive transmission with a custom 10-inch, non-damper-style, billet converter with stall speed tailored to the engine’s specifications.
Basted on a stock AOD two-wheel-drive short shaft transmission, the first step to Level IV performance begins with qualifying the case, high-pressure washing, and bead blasting. Then the case is rewashed and re-inspected before it goes to be painted. After the case is painted and the internal components are cleaned and thoroughly inspected, a technician gets to work on the custom remanufacturing process.
Reassembly starts with a master overhaul kit with Kolene steels and Raybestos racing frictions. Two valve body reprogramming kits improve shift timing and quality and a high-rpm governor assembly as allows for max throttle upshifts at the maximum engine rpm. A complete bushing kit, new Torrington bearings, and new thrust washers are installed. The original equipment clutch drums are modified to accept expanded capacity clutch packs, thus increasing the torque capacity of the transmission.
An extremely critical component is the reverse input drum. Its main function is to provide a friction element by incorporating a one-way roller clutch for Second gear and friction surface for the fourth overdrive band. Gearstar replaces this drum with the latest generation diode clutch drum, which is superior to the OE seven-roller design. This wider drum allows for a Fourth gear band that is 30 percent wider and is made of a sturdy carbon-fiber material designed to tolerate higher heat and more extreme conditions rather than the original equipment paper lining. Further, the earlier cast-iron input drum is replaced with the late-model stamped steel input drum/shaft, the direct clutch drum is also replaced with the late stamped steel design, which provides a higher capacity clutch pack, the OE direct clutch third shaft is updated with a 300M billet shaft that eliminates any breakage concerns. A new Kevlar low-reverse band designed to tolerate higher heat and has better friction coefficiency is used and the standard Second gear three-disc clutch pack design is updated to a higher capacity four-disc design and a lightweight, high-performance drive shell replaces the heavier, inferior original equipment drive shell reducing internal rotating mass. An expanded capacity billet overdrive racing servo and updated servo apply pin, which engages the overdrive band, are also used. In short, every weak point in these transmissions is addressed to provide years and miles of trouble-free service.
Finally, because of the many various linkage configurations available from Ford, Gearstar Performance uses a Lokar 360-degree adjustable shift linkage assembly. Lokar also provides the throttle pressure signal delivery cable system and an extra capacity cast-aluminum pan is part of the package, although other pans, such as chrome and polished aluminum, are available on request.