Jim Smart
November 10, 2010

Ford's Automatic Overdrive (AOD) transmission arrived in 1980 in full-size Fords, Mercurys, and the Lincoln Continental. As the AOD became available in more applications during the 1980s, including the 5.0-liter Mustang in '84, Ford improved reliability and performance, which is why we suggest opting for the newest version possible for your AOD project. It is a fiercely reliable automatic transmission if you do your homework and take proper care of it.

Both the AOD and AODE (4R70W) make outstanding transmission swaps for older Mustangs with vintage C4, C6, and FMX automatics because they provide overdrive with its resulting improvement in fuel economy and cruising comfort. You get better fuel economy because overdrive lowers engine rpm at cruise speeds by nearly 1,000 rpm, depending upon axle radio and tire size. If you run 3.50:1 rear end gears, you can expect approximately 2,000 rpm at 70 mph depending on tire size. And if you desire crisp acceleration, you can go with 3.89:1 or 3.91:1 gears for rocket ship acceleration along with respectable rpm range at highway speeds.

A point to remember: AOD is direct drive once you are in overdrive. Instead of torque converter slippage and inefficiency at cruise, power passes directly into the overdrive unit via an inner shaft once you've passed 40 miles per hour. It does this via internal lock-up at the overdrive unit instead of the torque converter.

Unless you intend to pump more than 350-400 horsepower through an AOD, you don't have to be concerned about durability. The AOD's rugged internals are based on the vintage FMX transmission, a cast-iron Borg-Warner three-speed automatic that came in many '69-'73 Mustangs.

We're building an AOD transmission at AMMCO Transmissions for Chris Jones' "It Takes a Village" '67 Mustang project at Dave Stribling's DVS Restorations in Crawfordsville, Indiana. Three years ago while driving his mother's '67 hardtop, he experienced the misfortune of a bad accident on a rain-soaked Los Angeles freeway, totaling the car. Because Chris' mother purchased the car new, it has tremendous sentimental value. When the Vintage Mustang Forum (VMF) heard about the unfortunate event, members came to the rescue. Stribling offered to repair the body and we offered to help with an AOD, Currie 9-inch, and a 5.0-liter engine.

We managed to find an AOD transmission out of a '91 5.0 LX Mustang. Although the optimum trans would have been an AODE because it is an electronically controlled transmission with a lot of nice improvements, we had to go with what was available.

If you're looking at a pile of AOD transmissions, it isn't always easy to identify them. The AOD is easily identified from the earlier C4, C6, and FMX by its integral bellhousing and case along with a 14-bolt "Metric" pan, also identified by the Ford corporate oval. If you're lucky, you will find a unit with its original identification tag located at the lower left tailshaft housing bolt. Because so many of these units have been rebuilt and their tags discarded, it's often challenging to identify them. The biggest differences lie in vehicle application, weight, engine, and axle ratio. Shift programming is going to vary as much as fitment depending upon vehicle application.

The first place to begin identification is the bellhousing-you want a small-block Ford six-bolt bell pattern. It's easy to get the small-block pattern mixed up with the 4.6L/5.4L Modular V-8 pattern because both are similar at a glance. Look for a two-bolt starter pattern for small-block Fords and 3.8L/4.2L V-6 engines; the Modular V-8 AOD/AODE uses a three-bolt starter pattern. You will want to avoid the V-6 version, which has the same bellhousing bolt pattern, because there are fewer clutches inside.

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According to Baumann Electronic Controls, another thing to watch for is input shaft length. Some applications have a one-inch longer input shaft. Another issue is the output shaft housing bushing outside diameter. Some have a larger slip yoke, which calls for a larger output shaft bushing (F3LP casting number). Baumann says this won't adversely affect your swap because all you need is the appropriate slip yoke and you're good to go. AOD and AODE extension housings are interchangeable, which makes it even easier.

AOD/AODE high-performance units (for the '93-'96 SVT Lightning F150, for example) have a wide-ratio gear package, which means it is good for you to know where your unit came from before laying down the cash. Pull the pan and look for a drain slot in the ring gear. This is your first indication you've found a wide-ratio unit. Baumann says all AODE/4R70W units from '96-up are wide-ratio units.

When we think of AMMCO Transmissions, thoughts turn to all the clichés associated with chain-shop auto repair-shoddy quality, inaccurate estimates, and a question of trust. In light of our positive experiences with AMMCO, it's easy to see why this nationwide chain of transmission shops remains successful, trusted by thousands of customers every day.

AMMCO's network of professional auto repair shops knows how to troubleshoot and service the transmission you have, not something plucked from a warehouse full of remanufactured cores. What's more, AMMCO services only what your Mustang needs and nothing more. If it's a simple problem like a ruptured servo seal, stuck valve body piston, failed vacuum modulator, or leaking pan gasket, it's an easy fix that doesn't require a complete transmission rebuild. At AMMCO, the news isn't always bad or expensive.

Neill Evans of AMMCO in North Hollywood, California, welcomed us into his shop and introduced us to Andrew Gricol, who dropped in from another San Fernando Valley AMMCO to help with our AOD project. Andrew has 30 years of experience with automatic transmissions and knew what we needed for our street AOD build.

We're going to fit our AOD with a B&M Trans Kit and 2,400 rpm stall-speed, high-performance torque converter. The difference between a stock AOD torque converter and our B&M unit is the lock-up feature. Instead of converter/overdrive lock-up and direct drive at approximately 40 mph, the B&M converter stays in torque multiplication mode, which provides good on-demand power with a gentle nudge of the pedal.

In this article, we're not taking you through a step-by-step rebuild of an AOD transmission, but rather we're touching on the important points you need to know when it's time to rebuild an AOD for either a classic or late-model Mustang.

AOD for Classic Mustangs
It used to be challenging to put an AOD in '65-'73 Mustangs, but no more. A number of conversion kits are now available for AOD swaps. Aim for the sturdiest transmission crossmember you can find that is also easy to install. Quality and engineering speak for themselves with these kits.

Performance Automotive and Transmission Center has just about everything you need to put an AOD in your classic Mustang. The AOD Dominator Junior package, which includes transmission, is rated to 550 horsepower. It will bolt up to everything from a 289 to the 351C using a 164-tooth flexplate. You also get a custom crossmember, Lokar throttle valve cable kit, correct speedometer drive gear based on axle ratio and tire height, 164-tooth flexplate (28- or 50-ounce offset balance), locking top dipstick and tube, and available transmission cooler. Cost for the Level 2 high-performance kit and transmission is approximately $2,329 plus $40 shipping. For stock applications, it's $1,499 plus shipping. Carburetor adaptor and shift lever kit are extra.

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TV Cable Adjustment
The AOD's TV (throttle valve) cable adjustment isn't much different in function than kick-down linkage adjustment on old C4s. Where the C4 differs is its two means of upshift/downshift modulation-vacuum modulator and the kick-down linkage. The AOD has a single TV cable controlled by the accelerator pedal position. Where it gets tricky is the finite nature of the TV cable adjustment. Get it wrong and you risk burning up the transmission. Even though the transmission might be shifting smoothly, this doesn't mean the TV cable is properly adjusted.

First, if you want to do this by the book, you're going to need a 0-100 psi pressure gauge to screw into the TV pressure tap on the right-hand side of the transmission. It is the middle plug in a trio of plugs near the tailshaft housing. You will need a long hose to get the gauge where you can read it. The engine should be at operating temperature at idle.

If you have a carbureted or CFI (Central Fuel Injection) vehicle, Ford says to obtain a TV control pressure gauge block (#D84P-70332-A) or fabricate a block-dimensions are .390-.404-inch thick (for carbureted and CFI engines only). You can also use a 7/16-inch bolt shank as a gauge. The engine throttle position solenoid needs to be disconnected and at rest. The gauge block or 7/16-inch bolt shank should fit perfectly between the carburetor throttle lever and TV control pressure gauge block and TV lever adjusting screw. Adjust the screw for a perfect fit. Transmission control pressure should be 28-38 psi. Optimum pressure is 33 psi. Turning the TV pressure adjusting screw should raise control pressure 1.5 psi per turn clockwise.

If you have an SEFI 5.0L or 5.8L engine, the TV cable adjustment is located at the throttle body with a non-adjustable end at the transmission. First, unlock the TV cable adjustment tab. Have someone hold the accelerator pedal to the floor. Make sure the throttle is at its idle stop position. With the accelerator to the floor, lock the TV cable adjustment tab, which locks in the adjustment. Mark the TV cable adjustment at the notches with a file or knife. This is your AOD's maximum TV cable location. Unlock the adjustment tab and slide the adjustment toward the exposed cable 5/16-inch. Lock the adjustment tab. Make a new mark, which is the minimum TV cable location. Scribe another mark midway between the maximum and minimum TV cable marks. Move the adjustment to the center and take a test drive.

Rule of thumb with a couple of transmission shops we've consulted is to have someone hold the accelerator pedal to the floor with the TV cable adjustment tab unlocked. Then connect the TV cable to the throttle and lock the adjustment tab. Begin your test drive program. Adjust the TV cable one notch at a time until you achieve 28-38 psi control pressure (ideally 33 psi).

If you don't have a pressure gauge, observe when upshift and downshift points occur. Upshifts should be firm and right on time. Overdrive should arrive at 40 mph under mild acceleration. If upshifts occur too soon, the TV cable needs to be adjusted tighter by one notch, then test drive again. If upshifts are too late, you have too much TV cable tension, so back off one notch at a time.

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