In 1980 Ford introduced the AOD (Automatic Overdrive) transmission in an attempt to fulfill American consumers’ demand for better fuel economy. The AOD was Fords first automatic overdrive and its introduction preceded GM’s 700r4 by 2 years. The AOD was introduced to the market with somewhat mixed results. The overdrive feature definitely proved appealing; however, the transmission was not without its faults. Upgrades to the transmission would develop over time, which would include an improved oiling system and later a more electronically controlled version known as the AODE/4R70W. The automotive aftermarket would further add upgradeable components to handle higher horse powered applications. As the reputation of AOD improved, so to would the popularity of the transmission. The 30 year reign of the AOD has earned it the respect it deserves as one of the most popular Ford transmissions for conversions.
Like many transmissions, the AOD design concept was based on existing technology. Ford’s engineers basically used Ford’s FMX transmission planetary gear set to develop the platform for the AOD. The gear train utilizes a compound, six pinion planetary gear set, incorporating one planetary carrier with a set of short and long pinions, rather than two or three single planet carriers. The design was most likely used because of the minimal modifications needed to incorporate an overdrive to it. It is safe to say, the FMX, AOD and AOD-E/4R70W are the only modern Ford transmissions who all share this compound planetary design.
The AOD can be identified in numerous ways. The unique 14-bolt pan is by far the easiest way. The pan is almost square-like but the back two corners being tapered off a little more than the front corners making the pan look like a baseball home plate with the front point cut off. At least on some oil pans reveal castings of “Automatic Overdrive”, The Ford Oval logo and the word “Metric”. The “metric” stamp has more to do deal with internal components as none of the hardware to install the transmission is metric. Further information on the transmission may also be found on the transmission. This includes a transmission tag located near the rear mating surface of the transmission. This tag includes many numbers; however, the first three-letter code on the top of the tag will say PKA (later AOD-E units with electric overdrives are designated as PKC). Another way to identify the AOD can be accomplished by referring to the driver's door tag. Ford lists the transmission codes on the Vehicle Certification Label. The single letter code is located on the bottom of the label directly below the abbreviation
TRANS. The AOD transmission will have a "T" designation for rear-wheel drive vehicles.
The external appearance of the AOD is considerably different than its C4 counterpart. Unlike the removable bellhousings common with the C4, The AOD was designed with a one piece case with an integral bellhousing similar to that of the C6. The non removable feature of the transmission does however limit some of the engine choices for conversions. The overall length of the AOD is 20.5”. The gear ratios are 1st 2.40, 2nd1.47, 3rd 1:1 and 4th gear providing an impressive overdrive of 33%. The AOD weighs 150 pounds, approximately 40 lbs. heavier than a C-4 transmission.
The selection of an AOD is something to take into consideration especially since the development of the transmission included some noteworthy improvements. The first versions of the transmission had a satisfactory yet improvable oiling system. Ford would eventually change the oiling system in 1988. When Ford changed the oiling system, the design of the output shaft also changed. Advance Adapters supplies a new output shaft for a majority of our conversion kits. Most of these supplied shafts are available for both the older and newer designed transmissions. It is imperative you order the correct replacement shaft for your AOD. We also highly recommend that you research and discuss some of the upgradable options available for the AOD. An experienced transmission shop should be able to explain these options.
The AOD would continue to be one of Fords primary transmissions for over 13 years. In 1991, the AOD would evolve into the electronically controlled AOD-E and with it the transmission would feature some attractive improvements.