Few people work inside their...
Few people work inside their cars' automatic transmissions, but chances are excellent that owners will handle the undercar heave-ho. While it would be nice to have a transmission jack such as this, you can do the same with a floor jack and a friend. Be sure to get the chassis supported high enough in the air to clear the height of the transmission's bellhousing atop the floor jack.
The AOD was not a clean-sheet-of-paper design from Ford-it was based off the venerable three-speed C4 automatic.
Now that Ford's automatic overdrive transmission has been around for so long, we sometimes forget it was really the first widely used overdrive automatic gearbox in the United States. But it was, making its debut in 1980 on passenger cars, then showing up in Mustangs from 1984 to 1993. Even then, the AOD was replaced by itself, dolled up with electronic shifting controls as the AODE in 1994.
While not thought so at first, the AOD has proven a fairly stout gearbox-stout, that is, if given the proper upgrades. And considering the numerous methods of arriving at major 5.0 horsepower, it's a good thing for auto-shift fans that the AOD can be readily modified to near-bulletproof status.
This is especially true for Ricky Best. Well known in the Mustang world as racing coordinator at Vortech Engineering, Ricky recently acquired a '93 coupe as a street/strip project vehicle for himself. And, while cumshawing a V-1 T-Trim blower onto it was reasonably easy (do you think?), he knew his little coupe's stock AOD would never make it without upgrading.
Recalling that one of the original AOD pioneers was reknowned automatic-transmission specialist Art Carr, Ricky headed off to California Performance Transmission, where Art does business these days. That's where we tagged along to review what an AOD should get when being prepped for modern performance use.
At California Performance Trans-mission, we reviewed what makes an AOD fail to tick when belted with more torque than it was designed to handle. A four-speed automatic with an overdrive top gear, the AOD has several weak points in high-power applica-tions. For starters, the Third gear (sometimes called "direct") clutch pack has only five "clutches and steels." This is a minimal number, and the arrangement has difficulty transmitting torque without slipping.
We're showing the first step...
We're showing the first step in disas-sembly-removing the torque converter-right away because it best illustrates the AOD's two-piece input shaft design. It's easy to see how the power path from a locked-up torque converter is sent into the bowels of the transmission by the smaller inner shaft. Disassembly is also a bloody mess of gushing ATF as fluid spills from the torque converter and tranny innards.
By giving up the lock-up torque...
By giving up the lock-up torque converter, CPT is able to use its own single-piece input shaft. This is a must-do operation on a performance AOD, otherwise the two-piece shaft absolutely will snap at the first hard shift and you'll be walking home.
These are the upgraded CPT...
These are the upgraded CPT parts for the direct (Third and Fourth gears) drive drum. The seven-pack bits are Raybestos clutches and steels; the single ring is the thinner CPT pressure plate; and the much lighter, faster accelerating drum (or basket) is in the background. The pressure plate is thinner to accommodate CPT's two extra clutch elements.
There is a reverse drum in...
There is a reverse drum in the AOD, and it uses a one-way ratcheting device-or sprag-to engage reverse. The stock sprag is a lightweight, pressed-steel and plastic-bushing birdcage containing some delicate rollers and ratchets. It's seen here standing up in the heavier race it runs inside of. In the background is the heavy-duty "dial sprag" CPT uses. It uses a much heavier spring-loaded ratchet that gives off a satisfying "clack, clack, clack" when rotated. Compared to the stocker, it's bombproof. Not showing is the reverse drum, which uses beefy dog-teeth lugs to engage the dial sprag, rather than the undulating ramps of the stocker-altogether worlds stronger than stock.
The stock 1.5-inch-wide OD...
The stock 1.5-inch-wide OD band is obvious when laid next to the 2-inch-wide CPT band. More band area means higher clamping force, so it can hold more torque without slipping.
The OD clamp is applied by...
The OD clamp is applied by pressure put against a servo piston. Ford has used A (largest), B, and C (smallest) pistons in AODs. All late-models of any interest came with B servos. CPT puts A servos in all its gearboxes for maximum clamping force.