Jim Smart
February 1, 2000

Step By Step

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Here’s everything you’re going to need to install high-tech overdrive in a classic. Our core is an ’80 vintage Ford automatic overdrive that’s been professionally rebuilt by Auto-Rite Transmissions in Van Nuys, California. It has all the good parts, the AODE drum and clutches, a more current ’89-and-up AOD valvebody, and additional clutches where necessary. Windsor-Fox Performance Engineering provided us with the AOD crossmember, manual linkage, the throttle valve cable setup for carbureted vehicles, and the AOD-compatible flexplate. Mustangs Plus sent us the aluminum driveshaft that’s a bolt-in swap.
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Our ’67 Mustang’s factory original C4 Cruise-O-Matic is actually smaller than the AOD to come. The AOD takes up the same amount of space as a C6 big-block transmission, which means the AOD will fit just fine.
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To prevent a nasty mess, drop the pan and drain the C4 of its transmission fluid. The tiny pan doesn’t hold much. Make sure your drain pan can handle 6-9 quarts. The torque converter alone holds 4 quarts.
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Our Mustang’s original driveshaft is a two-piece design—two shafts separated by a rubber vibrasorber. This type of shaft was common with Cruise-O-Matics to absorb vibration.
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We’re going to replace ours with a 50-inch aluminum shaft from Mustangs Plus.
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Next, remove the speedometer cable. Because the AOD employs the same type of drive and driven gears, no modifications or replacements need to be done in this area. As long as your rear axle ratio remains the same, there’s no need to change the gear. The ’67 speedo cable will fit the AOD.
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Remove the torque converter dust cover and remove the four torque converter retaining nuts.
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Hand-crank the engine to expose all the nuts. If there’s a drain plug, we suggest draining the torque converter at this time.
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Support the engine with a 2x4 as shown to protect the oil pan and use a jack for control.
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There are several items on C4 transmissions that must be disconnected. The vacuum modulator receives its vacuum from the engine’s intake manifold. Go topside and disconnect the vacuum line...
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...and then bottomside at the modulator
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Don’t forget the backup light/neutral safety switch leads, which must be disconnected.
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Remove the dipstick tube, and then disconnect the shifter and kickdown linkages
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Two line wrenches—1/2-inch and 5/8-inch open-end—get the transmission cooler lines
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With the C4 transmission safely supported with a transmission jack.
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Loosen the aft mount and remove the crossmember.
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Six bellhousing bolts spell freedom for the vintage C4. A 5/8-inch socket gets the job done.
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Once the transmission is separated from the engine, we’re ready for removal.
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Ford’s AOD transmission is an easy swap for classic Mustangs. Only a pinch longer than the C4, and certainly more efficient, the AOD fits our cradle nicely.
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The AOD is configured two ways, depending on whether the vehicle is column- or floor-shifted.
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Manual linkages pointed down are for steering column–shifted vehicles. The linkage is 180-degrees opposite for floor shifters.
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To rotate the manual linkage 180 degrees, you must carefully drop the valvebody, loosen the manual linkage nut, and turn the lever 180 degrees (arrow a). Then, tighten the nut, making sure the centering pin (arrow b) in the case remains and that both the manual and throttle valve (kickdown) linkages are properly reinstalled inside. Reinstall the valvebody and torque the 8mm bolts to specs.
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The AOD has a consolidated backup light/neutral safety switch, which calls for a special adaptor plug and harness available from Mustangs Plus. With the Mustangs Plus harness, just plug it in and forget it. Be sure to specify the model year of your Mustang when ordering from Mustangs Plus.
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Remove the C4’s flexplate, which is not compatible with the AOD.
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Next, remove the C4’s separator plate and install the AOD’s aluminum piece.
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A separate dust cover fits the void below.
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Whenever you’re ordering an AOD flexplate from Windsor-Fox Performance Engineering, be sure to specify engine type. Small-block Fords before 1982 were 28-ounce offset balanced (arrow).
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What’s more, don’t forget to give the bolt threads a thin application of sealer prior to installation. Torque the bolts to 85 lb-ft in a crisscross pattern. Double-check your work.
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From 1982 and later, they have a 50-ounce offset balance weight. Install the wrong flexplate and you will experience bad vibrations; don’t make this mistake. Because the flexplate can be installed using only one combination of crankshaft bolt holes, there’s no way to goof up this one. Pay close attention to the bolt holes.
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The AOD’s transmission cooler lines install similar to those of the C4’s . You will have to either fabricate new lines or order a set from Mustangs Plus. These adapters (arrows) are available from your Ford dealer.
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This is a Continental torque converter from Auto-Rite Transmissions, which has furnace-welded fins for structural integrity. We’re feeding the empty converter 1 quart of Motorcraft Mercon automatic transmission fluid, which will prime the front pump and get the converter filled during engine startup.
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Because it is easy to improperly install the AOD’s torque converter (with catastrophic results), you must pay close attention to detail.
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Locate the flat spots on the converter snout and front pump rotor. Place both at 12 and 6 o’clock, and then slip the converter snout into the pump rotor. If the converter is properly seated, its face will be approximately 13/4 inches from the bellhousing mating surfaces. Rotate the converter and determine feel. The rotor should turn with the converter shell.
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Raise the AOD into position. Keep a close eye on the torque converter because it can slide forward and out of the front pump rotor. If the torque converter will not turn when you mate the bellhousing to the engine, you need to lower the transmission and remate the converter and front pump. Remember that with an AOD, you’re marrying not only the converter and pump, but also the separate, inner overdrive shaft. You’re going to need slightly longer bellhousing bolts for the AOD. The C4 bellhousing bolts are nearly 1 inch too short for the AOD’s thicker casting.
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Use the C4’s transmission mount. Some installations mandate altering the mount’s holes for adjustability.
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Transmission mount bolts are metric in this case, which calls for a 12mm, 1-inch-long, coarse thread bolt.
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The Windsor-Fox crossmember is installed next and retained with Allen bolts supplied by Windsor-Fox. Line up everything and torque the mount and crossmember.
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Clearance problems reared their ugly heads with our exhaust system. The Windsor-Fox crossmember did not clear the custom exhaust system on our ’67 convertible. This isn’t the fault of Windsor-Fox, but an unfortunate aspect of the transmission swap. Sometimes custom installations clear and sometimes they don’t. We will have a new H-pipe fabricated for this installation.
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Windsor-Fox provided us with an AOD manual linkage rod, which ties the Mustang’s factory shifter (arrow) with the AOD.
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The rod attaches as shown to the AOD’s manual bellcrank (arrow). A special coupling attaches the rod to the vintage Mustang shifter. Simply tighten the coupling with an Allen wrench. As you can see, our AOD bellcrank is positioned for a column shift. As we suggested earlier, you must drop the pan and valvebody to turn up the bellcrank 180 degrees for a floor shifter.
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The throttle valve (TV) cable setup from Windsor-Fox enables you to run the AOD with a carburetor. For classic Mustangs, anchor the cable at the bellhousing boss (arrow) as shown, and then install the cable’s lever at the TV shaft located at the manual control linkage. The TV cable does for the AOD what the vacuum modulator and kickdown linkage did for the C4. Cable tension and position directly affect upshift timing and quality.
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The best way to adjust the TV cable is to install a pressure gauge at the transmission’s pressure port and adjust the cable until the gauge reads 35 psi at idle in Neutral or Park. This adjustment is critical, because if you incorrectly adjust it, you risk transmission failure. See a trusted transmission shop if you’re in doubt. The rule of thumb here is shift quality. If the transmission shifts too soon, you don’t have enough cable tension. If it shifts too late, or not at all, you have too much tension. Attaching the TV cable to the carburetor is simple. Always remember that the throttle should pull the cable.
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Our Mustangs Plus aluminum driveshaft is ready for installation. Lubricate the yoke with Mercon automatic transmission fluid before installation.

Wouldn’t it be nice if you could restore a classic Mustang in such a way that it would yield closer to 30-mpg highway, with less wear and tear on that vintage 289? Turn on and tune in to Ford’s automatic overdrive transmission for classic Mustangs. The automatic overdrive (AOD) transmission first appeared in new Fords and Mercs in 1980 and has steadily improved since. It’s a four-speed automatic transmission where Fourth gear is Overdrive—actually the reverse of what your engine experiences in gears 1 and 2 in conventional automatics.

In conventional automatics, such as the C4, C6, and FMX, First and Second gear are geared where the engine turns faster than the output shaft and driveshaft. This gives the engine mechanical advantage because it doesn’t have to work as hard under acceleration. Lower gear ratios allow us to make the most of the engine’s power output. Third gear, or final drive, puts the engine in straight drive at the same ratio as the rear axle gears. For example, if you have a rear axle ratio of 3.25:1, this means the driveshaft rotates 3¼ turns for every revolution of the drive axles and the engine is turning at the same speed as the driveshaft. This is how it is with a C4, C6, or FMX three-speed automatic.

The AOD has First, Second, and Third gears, as do the old three-speed automatics. However, it shifts a third time into Overdrive, which lowers engine rpm via a higher final-drive ratio inside the transmission. Most late-model automatics have a locking torque converter, which engages when the transmission shifts into Overdrive. This gives the engine a direct connection with the overdrive unit without the slippage of a fluid-coupling torque converter. The AOD doesn’t have a locking torque converter. Instead, it has a shaft within a shaft that goes straight from the torque converter shell—driven by the engine—to the overdrive unit. Lean on it in Overdrive and it feels like a stick shift in high gear. The engine labors mildly and you feel a solid connection with the drive axle. This saves fuel and reduces wear and tear because there isn’t the slippage we experience with a fluid coupling. Lean on the gas hard enough and the overdrive comes out of lockup, putting the engine back in touch with the torque converter, which gives us more power.

A torque converter does exactly what the name implies. It multiplies the engine’s torque via a fluid coupling that’s tied to the transmission’s front pump and input shaft. The input shaft turns clutches and planetary gear sets to get power to the driveshaft yoke. Whenever a torque converter goes into lockup in final drive or Overdrive, we’re tying the engine directly to the driveshaft, so to speak, for slip-free power transfer. In lockup, we no longer have torque multiplication—just a one-to-one direct link. AOD For A Classic

There are two basic answers for classic Mustang buffs looking for overdrive efficiency. The Gear Vendors overdrive unit for C4 and C6 transmissions enables you to spline overdrive into your antique slush box. All you have to do is shorten or replace the driveshaft and dovetail the Gear Vendors unit into your golden oldie.

Ford’s AOD offers a more economical answer for enthusiasts needing overdrive performance without the high price tag of a bolt-on, aftermarket retrofit. The Gear Vendors overdrive is an outstanding answer for enthusiasts looking to pump 500-1,000 hp through a driveline. Considering most of you who read Mustang Monthly won’t be building 500-1,000hp stump pullers, we’ll bet you’re game for the more affordable AOD solution. There are a lot of horror stories about AOD conversions and their complexities, but Windsor-Fox Performance Engineering makes it easy to bolt on an AOD behind your vintage Ford small-block. And we’re going to show you how.

Our test mule is a mildly modified ’67 Mustang convertible with a carbureted 289 engine. We’re going to retrofit a garden variety small-block Mustang with an ’80s vintage Ford AOD custom-built by Auto-Rite Transmissions in Van Nuys, California. Auto-Rite performed all the modifications necessary to bolster the performance of a Ford AOD: heavy-duty AODE components, more clutches, and the appropriate valvebody mods to firm up the shift. Now we’re ready for installation.