What Is A Ford AOD Transmission?

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The Ford AOD transmission revolutionized driving for the American public when it was introduced in 1980. What exactly makes the AOD transmission so reliable?

The Ford AOD (automatic overdrive) was a 4-speed transmission developed from 1980 - ‘93. It was the first 4-speed automatic developed by an American automaker and ended up in most full-sized Ford, Mercury, and Lincoln models. The AOD-E replaced the transmission with the use of electric controls.

Ask anyone who lived through it, and they will tell you that the seventies brought the end of innocence for the American driver. Shocked by two oil embargoes that skyrocketed fuel prices, and a national speed limit everyone hated, Americans needed a powerful vehicle that sipped gas. Since there was a strong dislike of foreign imported four-cylinders, American designers scrambled to offer ways to improve the efficiency of their vehicles. Ford knew that Americans loved their mid to large sedans, so they developed an automatic transmission with overdrive (AOD). Americans could cruise the highways to their heart’s delight once again. But what exactly is the Ford AOD? Why makes it so great? What kinds of problems did it have? Let’s give the Ford AOD transmission some careful analysis and determine how this transmission helped the American driver grow up and face the harsh realities of the real world.

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What Is The Ford AOD Transmission?

The Ford AOD was a four-gear automatic transmission that used the top (4th) gear as overdrive. Ford’s first full-scale overdrive transmission departed from older three-speed transmissions like the C4, C6, and FMX. While the transmission used a Ravigneaux gearset (which Ford previously used on the FMX), the effort was a new direction for the automotive giant.

The advantage of the AOD transmission was that it lowered engine revolutions during the cruising fourth gear, providing significantly improved fuel economy. Higher ratios in the lower gears boosted performance and provided more torque for the rear axle, which was great for acceleration.

The transmission was significantly heavier than other three-geared automatics, even though it was just as wide and slightly shorter. To ease production issues, Ford designed the unit to be married directly to the 289, 302, 351C, and 351W using the same bell housing bolt pattern.

How Did the Ford AOD Work?

The Ford AOD was a split shaft system with one rod connecting to a gear clutch housed in the torque converter. This outer shaft handles the First, Second, and Reverse gears. Then an inner shaft is connected/driven off the motor at a 90-degree angle, handling the Overdrive. The third gear splits between the two shafts (60% powered by the engine, and the remainder is picked up by the smaller inner shaft powered by the torque converter).

In addition, the system used a mechanical hydraulic throttle valve rod/cable to regulate shift points. The cable extended from the throttle to the transmission to respond more effectively to the driver’s intentions. The transmission line pressure would increase as the throttle engaged, dictating the shift speeds. The TV cable could be adjusted for correct transmission operation by moving a plastic connection piece connected to the throttle body. Some early AOD transmissions suffered from TV cable bushing failure, which created shift lags, erratic performance, and even complete transmission loss.

What Are the Specs of the AOD Transmission?

We’ve listed some of the specifications of the Ford AOD below. Improvements to the AOD during its production run created different gear ratios for high-performance SVO Mustangs and certain model F150s. (The gear ratio for these vehicles is 1st, 2.84:1; 2nd, 1.55:1; 3rd, 1.00:1; OD, 0.67:1; Reverse, 2.00:1).

Item Specification
First Gear Shift Ratio 2.40:1
Second Gear Shift Ratio 1.47:1
Third Gear Shift Ratio 1.00:1
Fourth Gear Shift Ratio 0.67:1
Reverse Gear Shift Ratio 2.00:1
Weight 150 lbs dry
Transmission Case Material Aluminum
ATF Fluid Mercon V (6.5 quarts w/o converter)
Throttle Valve Hydraulic TV cable
Output Splines 28 output
Pan Bolts 14

What Vehicles Used The Ford AOD?

For the 1980 model, the first vehicles equipped with the Ford AOD were the down-sized Lincoln Continental and Mark VI. (It was also offered as optional equipment for the Mercury Marquis, Cougar, Ford’s LTD, and Thunderbird).

With the introduction of the AOD, Lincoln trumpeted a 41% increase in fuel economy. Ford quickly pointed out in their LTD brochure that their economical V8 offered something no one else did, a “full-sized car that not only meets today’s demands for efficiency, but one that provides remarkable roominess and comfort.”  

It wasn’t long before GM and Dodge came out with their versions of the automatic overdrive, although the GM’s TH200-AR used the old 3-gear single system with an added 4th gearset (meaning it cost more to make). In 1982, GM modified its transmission with the introduction of TH700-R4, although the trannies tended to be unreliable.

The Ford AOD would make its way into almost every full-sized vehicle Ford, Lincoln, and Mercury made. The transmission was used in the Ford F-Series, Lincoln Continental Mark VI, and the Mercury Cougar for the longest production run (1980 - 93). In 1984, the AOD would appear in the Mustang and be a part of the legacy for over a decade.

Eventually, Ford modified the AOD transmission in 1992 with electronic throttle controls, a powertrain control module, and other modifications to formulate the AOD-E. While the two transmissions shared some similarities, the AOD-E was powered by electrically driven solenoids rather than the hydraulic throttle valve rod/cable of the AOD.

How To Identify A Ford AOD Transmission?

The easiest way to identify the Ford AOD transmission is to count the pan bolts (14-bolt pattern). Many early AODs have the Ford Oval and Automatic Overdrive stamped on them.

You can look at the transmission itself. The first three-letter code will feature a “PKA” designated the Ford AOD. (The AOD-E had a “PKC” code).

A final way is to look at the driver’s door tag. The bottom line on the tag will have a single letter (like a “T” for RWD) next to the header “TR” or “Trans.”

What Were Issues Regarding The Ford AOD?

Early automatics were troubled by several issues that kept Ford engineers scrambling.

Throttle Valve Cable Bushings

Since the AOD had a cable connecting the throttle to the transmission, the smoothness of the shift depended on input from the throttle valve function. While the TVC could be adjusted, the valve body had a history of loosening, which meant it had to be constantly readjusted. Improper TVC tensions caused a loss of fuel economy, and in some cases, complete failure of internals.

Input Shaft Failure

Because AOD transmissions use a split shaft system, the inner shaft (connected to the engine) operates part of the 3rd gear and the overdrive unit. These higher gears stressed the internals and created significant stress loads during operation. Early AOD inner shafts were not stable enough to handle the loads.

Best For Stock, Terrible When Pushed

While Ford eventually worked out the kinks in early AOD transmissions, the automatic overdrive gear did not like to be pushed hard. Many owners with engine modifications found that the internals could not hold up.