Ford’s Automatic OverDrive (AOD) transmission was introduced in 1980 as an answer to demands for higher fuel economy, lower vehicle emissions, and improved vehicle drive-ability. The AOD was a new transmission design into which various design features of existing Ford automatic transmissions were incorporated. The AOD was one of the first transmissions of its type in the automotive industry and also one of the simplest by design.
The AOD gear train design was based somewhat around the gear train of the FMX/Cruise-O-Matic transmission which (in one form or another) has been part of Ford’s automatic transmission history for decades. This gear train incorporates a compound (six-pinion) planetary gear unit, utilizing one planetary carrier, rather than two or three single planet carriers. This design was probably used because of the minimal changes needed to “add” overdrive to it. In fact, the FMX, AOD and AOD-E/4R70W are the only modern Ford transmissions which share the compound planetary design.
The reasons for using an AOD (or AOD-E), instead of a C-4 or C-6 transmission in your performance vehicle are obvious. The primary advantage of using an AOD is the potential for fuel efficiency with no resultant sacrifice in performance, thanks to the 2/3-1 overdrive ratio which made the AOD a clear choice for Ford Motor Company, as well as its customers.
For example, mathematically speaking, even a steep 3.73-1 rear axle ratio becomes a 2.49-1 ratio during fourth gear cruise (3.73 x 2/3 = 2.49), allowing about 1000 less engine RPM at highway speeds. Not only does the AOD provide a better cruising ratio than a three-speed automatic, but it also serves to further increase fuel mileage, engine life and overall efficiency by bypassing the torque converter in fourth (and partially in third) gear through the direct input shaft. This is a precursor to the A4LD, E4OD and AOD-E/4R70W transmissions which use a converter clutch to perform the same function under EEC control (providing much better performance).
The AOD-E/4R70W is the latest and best Ford performance transmission, and in our opinion, represents the foreseeable future of performance rear-wheel-drive automatic transmission technology.
Although the AOD is long been out of production and was problematic at first, we have been able to upgrade our rebuilt AOD units to be very reliable and affordable. We understand that our customers deserve the best Ford transmissions money can buy, and they deserve them.
We make sure pure value is built right into every transmission we sell. Call GotTransmissions.com for realistic answers to your questions for free. 866-320-1182.