If you're planning on swapping out your existing transmission, or are planning a project, some dimensions may help too. We'll assume you're not going to use a Ford-O-Matic or FMX here:

All the Ford automatics have good and bad points. The C4 is light, efficient, and small enough to fit under the floorpan of most vehicles, and is easily adapted to other engines thanks to its removable bellhousing, unlike other Ford automatics. It is a light duty transmission though, and in stock form the planetary system can fail, but C4s can be built to accept tremendous amounts of horsepower, up to 1,200 bhp depending on how they're modified, and by whom. This obviously depends on how much you want to spend and how you use your car. They also have the advantage, depending on your point of view, of being simple, with just a kick-down cable and no computer controls, electronics, or even TV cable to worry about. There are two tailshaft housing lengths available on C4s, the common version being 131/8 inches long, with some pickups and vans using a much shorter 65/8-inch version.

The C6 can withstand tremendous power in stock form, and has no inherent weaknesses, though they will rob power and are really suited to use with high horsepower big-block engines, because of their heavy rotating mass. The one-piece casing with its integral bellhousing means each C6 is limited to the series of engines its bolt pattern will accept, and its sheer physical size and length means it is awkward to fit it in many cars. Again, depending on the application, three different length tailshaft housings are available; 7 inches for trucks, 14 inches for passenger cars, and 17.4 inches in Lincolns.

The AOD can handle about 300hp and 250ft lbs of torque in standard form, but can be modified to withstand 700-800hp. However, in stock form, one of the most common problems is that the overdrive band has a tendency to burn up, and the lockup input shaft is notoriously weak. These are nothing that cannot be fixed however. There are actually two input shafts in an AOD, a hollow outer shaft that is driven by the converter and operates First, Second and Reverse gears, while the inner shaft, which runs inside the outer one, provides direct drive in Third gear, and is driven mechanically from the front cover of the converter. This is known as a split torque path. In Overdrive, all the torque is transmitted mechanically, as in a manual transmission. Upgraded and hardened input shafts, usually manufactured from chrome moly or billet are available. Upgraded valve bodies, often using an electric solenoid to control Overdrive, also improve the AOD.

If you're sourcing an AOD from a car, rather than buying an aftermarket version, you'd do well to grab the associated hardware, such as bolts, the four pin electrical connector for the backup lamps and Neutral sensor, dipstick tube, block plate, linkages, hydraulic fittings and even the driveshaft yoke to make your conversion easier. Note also that the AOD is physically larger than a C4, more akin to a C6 "around the waist," and may not fit your transmission tunnel without some modification. Also, remember the AOD doesn't use engine vacuum and a modulator valve like its predecessors to sense load, but has a throttle valve (TV) and hence requires a TV cable for the kick-down function. An improperly adjusted TV cable will trash the transmission so make sure it's fitted and set up correctly. The AOD also comes with two lengths of tailshaft housing, the shorter and more common one of just over 10 inches providing a transmission length similar to the C4. As can be seen in the preceding chart, while the C4 and AOD are only 1/2-inch apart in overall length, there's a 2-inch discrepancy in bellhousing to trans mount measurements, useful to know should you be swapping from one to the other. Oh, and the AOD uses a 164 tooth flexplate, while the C4 can use 148, 157 or 164 tooth ring gears.

While some people will prefer the AOD because it's not computer controlled, others will opt for the AODE, because it is! According to Phoenix Transmission Products' Greg Ducato again, "with the level of refinement in our daily drivers these days, we have new expectations of our hobby cars. The AODE makes such a difference in drivability. The curse of the AOD is its mechanically locked converter. In Third and Fourth gear it's locked up and loses all torque multiplication. Most AODs we sell are non-lockup. We use a stand-alone Compushift with our AODE transmissions, as you can manually raise or lower the shift points and adjust the lockup, without needing a laptop computer. It's all done via the Compushift display panel." So if you are planning on the AODE, you will need an AODE computer and transmission wiring harness, either OEM or aftermarket, from a company such as Compushift or Baumann Engineering.

Ford -O-Matic 228lbs
FMX 160lbs
C4 110lbs
C6 140lbs
AOD 150lbs
Trans Bellhousing
Face to Trans
Mount Length
Overall Length
From Bellhousing
To Tailshaft End
C4 20¼-inches 30½-inches
C6 22½-inches 33½-inches
AOD 22¼-inches 30¾-inches
E4OD 29 3/8-inches 37½-inches
SOURCE
Gearstar Performance Transmissions
132 N. Howard St.
Akron  44308
330-434-5216
www.gearstar.net
TCI Automotive
151 Industrial Drive
Ashland
MS  38603
888-776-9824
http://www.tciauto.com/
Phoenix Transmission
AK
866-744-3887
www.phoenixtrans.com
HGM
24009 Hawthorne Blvd
Torrance
CA  90505
310-787-9260
www.hgmelectronics.com