The Ford AOD Transmission

Add a gear to your automatic and recoup the cost in gas savings

The Ford AOD Transmission

Feature Article from Hemmings Motor News

May, 2009 - Jim O'Clair

Ford used the Cruise-O-Matic C-4 transmission for almost 20 years behind six-cylinder and small V-8 engines in literally millions of production cars. This three-speed workhorse was replaced in 1982 by the light-duty C-5 transmission, which was discontinued in 1986. Because of gas mileage mandates from federal requirements, Ford redesigned the C-4 into an overdrive automatic to lower highway driving ratios resulting in better highway MPG ratings. They called this replacement transmission the AOD, meaning automatic overdrive, and it became Ford's first automatic four-speed offering. Because the AOD is basically a retooled C-4, many classic car owners have discovered they can substitute this overdrive transmission into their '60s and '70s production vehicles relatively easily and reap the benefits of a lower final gear ratio and decreased wear and tear on their vintage small-block V-8 engine. The AOD was used originally on '80s and early-'90s Ford, Lincoln, and Mercury products and in the F-series pickups and E-series vans as well. Because Ford used these transmissions in so many production vehicles, the Ford AOD is relatively easy to locate at used parts yards and can be purchased for a reasonable price. The Ford AOD does not need a computer to function properly either. The throttle valve function is mechanically activated and the torque converter lock-up function was contained entirely within the transmission case. Ford later used this transmission as a basis for their newer overdrive versions, the electronic-overdrive AOD-E, which was used beginning in 1993 and in the 4R70W which was used on 1999 and up production cars and trucks.

The AOD transmission can be identified by its 14-bolt oil pan. The pan is basically square, but the back two corners are tucked in a little tighter than the front corners, making the pan look six-sided. Many of the original pans also have "Automatic Overdrive" and "Metric" stamped into them. The metric is true only because the internal parts are metric, but the external mounting hardware to install the transmission is not. You can also check for a tag attached to the transmission itself. This is located on the driver's side on the bottom bolt that attaches the tailshaft to the transmission body. This tag will have a three-letter code on the top of the tag that will say PKA. The AOD has the neutral safety switch mounted above the valve body on the driver's side of the transmission and the speedometer drive cable is attached to the vehicle speed sensor on the driver's side as well. This transmission uses a throttle valve linkage or cable assembly to regulate the shifts. The AOD is definitely bulkier than the C-4, weighing in at about 150 pounds, a full 40 pounds heavier than its predecessor. The majority of AOD transmissions have a close-ratio 2.40:1 first gear, but some SVO-equipped Mustangs and some 1992 and 1993 trucks came with a wide-range AOD with a 2.84:1 ratio. The overdrive ratio for all AODs was .067:1. You can purchase aftermarket-rebuilding parts that will adapt the standard 2.46:1 ratio transmission to the wide-ratio 2.84:1 configuration.

You will find a Ford AOD in these donor vehicles:

  • 1980-'92 Ford and Mercury full-size cars with both V-6 and V-8 engines
  • 1980-'92 Grand Marquis and Crown Victoria with 4.6 or 5.0 V-8 engines
  • 1983-'86 Ford LTD with a 6-cylinder engine
  • 1985-'90 Bronco with 5.0 V-8 engines
  • 1981-'93 Ford pickup and E- vans with V-8 engines
  • 1991-'93 Ford pickups and vans with a 7.3 liter diesel engine
  • 1980-'93 Lincoln (except Versailles) with V-8 engines
  • 1984-'93 Mustang and Cougar (both V-6 and V-8)
  • 1984-'86 Mercury Capri
  • 1980-'92 Thunderbird
(In Mustang, Cougar, Capri and T-bird vehicles only, transmission code PKA is an AOD)

If you have a choice of donors, in terms of strength and reliability, you prefer a unit out of V-8 truck, then V-8 car, and then V-6 truck. The V-6 car transmissions are the lightest-duty of the bunch, and the truck and V-8 car transmissions have a slightly longer tailshaft than the passenger car V-6 unit. Also, the 1988 and up units had a better main shaft lubrication than earlier units. You will want to look for pre-1986 transmissions for use in carbureted vehicles as they would have the proper shift linkage necessary for those cars. Transmissions used in 1987 and up Fords were for fuel-injected cars, and they used a TV cable activation.

The AOD is bolted to the engine by the use of an integral bellhousing. Because Ford small-blocks used the same bellhousing bolt pattern, the AOD will bolt directly to earlier Ford small-block engines. Measure the distance between your two top mounting bolts on the bellhousing to be sure. Installing the AOD in place of the earlier C-4 will involve moving the crossmember back about 2 inches and drilling new holes for the transmission mount. Aftermarket crossmembers designed specifically for the AOD and Tremec transmissions are available from Mustang and Cougar suppliers. Because of a Ford engine design change in 1981, when transplanting an AOD into a vehicle older than 1981, you must use a 1977-'81 C-4 flexplate and starter with the AOD lockup torque converter, otherwise the crankshaft balance will be off.

You can find AOD transmissions easily and for a reasonable price. Both passenger car and truck units we located were less than $600 used, making this exchange a relatively inexpensive project that could pay for itself over a period of time from the fuel savings alone.


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