Ford C4 to AOD transmission swap basics


When you get the transmission try to get all of the related stuff (bolts, electrical connector, dipstick tube, converter, yoke, block plate, linkages, levers, shifter, hydraulic fittings, etc.), will make this project a lot easier.

Extension Housing – There are extension housing variations among C4’s, with a short tailshaft (6 5/8 inch) used on some pickups and vans and a standard tail shaft (13 1/8 inch) used in most other applications. There are two tail shaft lengths on AOD’s. The short model is the one that is closest to the C4 in overall length. (10.1-inch)The short extension housing AOD was used in most passenger cars, 2WD F-150 trucks built after 11/81, and 83-85 E-150 vans. Don’t confuse the AOD with the AOD-E, which uses electronic control.

Converter Compatibility – The AOD transmission and torque converter are a matched pair. The AOD uses a hollow two piece input shaft (one shaft inside the other) for lock-up purposes and requires a specific torque converter.

Gear Ratios – The first three gears of the AOD and C4 are similar and the AOD has a 0.67:1 overdrive ratio

Physical Attributes the AOD weighs about 150 lbs. The AOD is beefier around the middle than the C4, The bosses on the AOD bell housing are thicker than those of the C4, so longer bolts are required. The hydraulic fittings on the AOD were larger than those of the C4. Two adapter fittings (1/4 ID pipe to 5/16 OD tubing are needed to mate the fittings on the transmission lines to the AOD case. AOD’s take a lot of Dexron-II transmission fluid

Transmission Crossmember and Insulator – The only bit of true fabricating is usually the transmission mount crossmember. While the AOD and C4 overall lengths are close the mounting pad for the insulator on the AOD is 2 inches farther aft, so the crossmember mounting point needs to be adjusted to fit.

Flexplate Diameter and Balance – One of the more important parts of the swap is to choose the proper flexplate for your application. The integral bellhousing AOD requires a flexplate with 164 teeth (approximately 14 1/4 diameter with an 11 7/16 torque converter bolt pattern) for proper starter placement and converter compatibility. The C4, however, uses a detachable bellhousing that is matched to one of three different flexplate sizes (148, 157, and 164 teeth). The 148 tooth flexplates are comparatively rare, having been used in cars like the V8 Mustang II. The 157 teeth flexplates were generally used in 289/302 small and mid-sized cars, while the 164 teeth flexplates were used in 289/302 full-size cars and 351W/351C applications. The C4 164 teeth flexplates and the AOD 164 teeth flexplates will physically interchange, but there are two balance weights to be concerned with. Part# OEM E0AZ-6375-A (164 teeth flexplate, 28.2 oz-in balance factor, 351W with AOD applications). If you’re swapping an AOD onto an ’81 or later 5.0 you’ll need the AOD flexplate (164 teeth, 50.0 oz-in balance factor, for 5.0 with AOD applications) OEM part number E2AZ-6375-A.

Block Plate – A block plate (the thin stamped sheet metal plate that fits between the engine block and transmission housing) which matches the large AOD bellhousing and provides the correct starter location and engagement depth for the torque converter snout in the crank pilot (assuming you have the right flexplate).

Driveshaft and Yoke – You can use a T-5 front yoke, since it is a stronger piece to begin with, plus it does NOT have the rubber isolator. The AOD/T5 yoke is desired but you can shorten the C4 yoke to get it to fit properly. You will need to shorten the driveshaft by the correct amount.

Speedometer Gear – The speedometer driven gear assembly from the C4, including the bolt and retaining clip, will fit into the AOD. There may be some variation with the AOD drive gear (the gear inside the tailshaft housing), so you may have to change driven gears for proper calibration.

Electrical Connections – The AOD uses a four pin electrical connector for the reverse/backup lamps and neutral sensing switch.

Throttle Valve Operation – The AOD does not use engine vacuum and a modulator valve to sense load. Instead, a throttle valve is used which moves proportional to throttle pedal travel. This is one of the most important parts of the swap to get right. When adjusting the linkage, it is safer to err on the side of hard shifts. There are a several ways of implementing the TV linkage and the linkages can be pirated from cars or trucks that came with AOD’s and carbs or throttle body injection. A rod arrangement was used on AOD cars equipped with carbs and TBI while a cable was used on SEFI cars. Remember, you’ll need a way to adjust the linkage to vary shift feel. Alternatively, you can purchase an aftermarket TV cable kits (available from Windsor-Fox, Total Performance, and others).

C4 and AOD Dimensions

Overall Length (bellhousing to tailshaft housing end, flat-to-flat):AOD – 30 3/4 inch
C4 – 27 3/4 inch
C6 – 28 1/2 inch or 28 3/4 inch

Distance from Bellhousing to Insulator Mount (flat to mounting hole centerline):
AOD – 21 3/4 inch / C4 – 19 3/4 inch

Flexplate Diameters
164 teeth – 14 3/16 inch (13 inch converter)
157 teeth – 13 1/4 inch (11 inch converter)
148 teeth – ?

Transmission Weights

AOD (without converter or fluid) – 150 lbs
AOD stock torque converter – 34 lbs
C4 (without converter or fluid) – 110 lbs
C4 torque converter – ? lbs
C6 (without converter or fluid) – 140 lbs
C6 torque converter – 30 lbs small block, 31 lbs big block

Ford Transmission Ratios Comparison
  Stock C4 Stock C6 WR C6 Stock AOD WR AOD E4OD
1st 2.46 2.46 2.72 2.40 2.84 2.72
2nd 1.46 1.46 1.54 1.47 1.55 1.53
3rd 1.00 1.00 1.00 1.00 1.00 1.00
4th —- —- —- 0.67 0.70 0.71

Balance Factor Information
1981-and-up 5.0 HO – 50.0 oz
1981-and-up 302 (non-5.0 HO) – 28.2 oz
Pre-1981 289/302 all 351W and 351C-400 – 28.2 oz


One thought on “Ford C4 to AOD transmission swap basics

  1. Bob,
    My Frankenstein Ford starter problem?

    I bought a 302 out of a 1985 Lincoln Continental that had a
    AOD trans. with 164 tooth flexplate with a 50oz. weight.

    I mounted a bellhousing off my c4 (pan fill 164 tooth) to the
    Engine Block using the 50 oz 164 tooth Lincoln flexplate and block plate.
    and the starter sqwalled and squeeked.

    Got a new flexplate (164th. 50oz.)
    got a new starter.
    Same Problem.

    I swapped out the c-4 and mounted a c-6 transmission
    and this show a lot of improvement but no cigar.

    All this testing has been done with the engine out of vehicle
    sitting on blocks. (Im sure Glad I tried this before engine installation).

    MY question is IS there a difference in the starter mount location Between
    AOD- C-4 and c6?

    I tried 3 different Starters
    3 different Flexplates (1980, original 1985 and new 1985
    2 different block plates.
    2 different trans (c-4 and c-6) I do not own a AOD

    Thanks Bob

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