Ford AOD transmission

AOD
Overview
Manufacturer Ford Motor Company
Also called AODE
4R70W/4R70E
4R75W/4R75E
Production 1980–present
Body and chassis
Class 4-speed longitudinal automatic transmission
Related Ford FMX
Chronology
Predecessor C4
C5
Ford FMX
Successor 6R

The AOD (for automatic overdrive) is a four-speed automatic transmission with overdrive. Introduced in 1980, it was Ford's first four-speed automatic overdrive transmission. The gearset design is based on the Ford "X" automatic transmissions used during the 1950s, 60s, and 70s. The AOD replaced many of Ford's older transmissions such as the C4, C5, and light duty applications of the FMX.

History

In 1962 Ford began working on a new type of automatic transmission that would emphasize fuel economy and driveability. The new transmission was built around the Ravigneaux planetary of the "X" transmissions. Where many transmissions had a fourth gear added on as an afterthought, Ford's new transmission was designed with a fourth gear integrated into the gearset. Because it was based on the X transmissions, its gear ratios from 1-3 were the same with the fourth being .67:1. The transmission featured a split-torque application for third gear as well as a lockup in the torque converter. The XT-LOD was initially abandoned in 1966 but design began again in 1974 as a result of rising gas prices. The project was shelved with a design that lacked a dampener in the torque converter but after the project was revisited a dampener ultimately made its way into the final design. The transmission was introduced when Ford started to downsize its full size line in 1979. Initially called XT-LOD (Extension Lock-Up Overdrive) its name was changed when revisited in 1974 to FIOD (Ford Integrated Overdrive) and then to its final name in 1979, the Ford AOD transmission.[3]

Applications:

Gear ratios

AODE

The AOD was redesigned with electronic controls in 1992, becoming the AODE. It was mainly intended for the new Modular V8 at first, but it was also adapted to the old AOD bell-housing for vehicles still powered by OHV engines. While the AOD, AODE and early 4R70W share some basic components like oil pans, gear sets (AODs and AODE can be retrofit with 4R70W gear sets), most of the internals are not interchangeable because the 4R70W and AODE use electronic solenoids to shift instead of conventional hydraulics. The transmissions are not interchangeable either, as the AOD only uses a throttle valve cable for operation. The AODE and 4R70W's shift points are controlled by the Powertrain Control Module (PCM) also sometimes referred to as the Electronic Engine Control (EEC).

Applications:

4R70W

A revised version of the AODE was released in 1993 with the Lincoln Mark VIII. Compared to the AODE, it has lower 1st and 2nd gear ratios for better take-off acceleration and was designed for better gearset strength. On vehicles powered by a 5.4 L V8, a stronger gearset is used than in normal duty 4R70Ws. In 1998, due to durability concerns, the intermediate one-way roller clutch was replaced with a mechanical diode providing extra holding capacity and longer service.

While there is speculation that the 70 can be multiplied by 10 to indicate the lb-ft of torque this transmission is capable of handling including torque converter multiplication, (i.e. 700 lb-ft of torque), there is no reliable source indicating this. In fact a Ford document stated that the 2003 "Expedition's 4R70W transmission is rated to handle up to 506 pound-feet of torque, which provides a large performance cushion beyond the peak torque rating of Expedition's largest available engine." http://web.archive.org/web/20040908180047/http://media.ford.com/products/presskit_display.cfm?vehicle_id=548&press_subsection_id=423&make_id=92 . It is more plausible that the number indicates the torque handling capability in N-m, as 506 lb-ft converts to 686 N-m which could be rounded to 700 N-m. The "70" may also refer to the transmission's torque capacity after torque converter multiplication which occurs at low rpm's when the torque converter is more "elastic". 4R70W indicates 4 gears, Rear wheel drive and Wider gear ratio compared to the AODE.

The gear ratios are:

Applications:

4R75W

In 2003 Ford revised the 4R70W transmission with a stronger ring gear that had 24 lugs, as opposed to 6, for the output shaft sensor (OSS) to read off of, a new torque converter, a revised front pump assembly, and a vehicle speed sensor (VSS) that compliments the OSS to improve shift quality and efficiency. These improvements allowed the 4R75W to handle more power while being more efficient and economical. While not used on all 2003 model year vehicles, the 4R75W/E transmissions eventually replaced the 4R70W/E.

Newer transmissions that are referred to as 4R70E or 4R75E have modifications that compliment Fords switching to throttle by wire. The PCM was given a more powerful microprocessor and Ford added a turbine speed sensor to the transmission. This allows the PCM to know the speed of the input shaft after the torque converter which is used in combination with crankshaft speed to detect the amount of slipping going on in the torque converter. This information provides PCM with the basis for fully electronic shift scheduling which limits "hunting" and fine-tunes shift speed and feel. It lets the PCM know what the torque will be in the next gear so it can choose the shift points based on the vehicle's projected performance in the next gear. Coupled with the electronic throttle strategy, the transmission computes the output torque required to maintain the vehicle speed, and chooses the correct gear and converter state accordingly.

Modification

The most practical modification for the 4R70W is the J-mod. It involves modifying the valve body separator plate and gaskets as well as changing or removing accumulator springs to alter the shift timing of the transmission. While these modifications can be done to 4R75W transmission, the results are not as dramatic as some of the details of the J-Mod (bigger holes in the separator plate and gasket) were done to the transmission in its design. These modifications are specified by one of the Ford engineers who designed the transmission. It offers faster engagement, quicker shifting, smoother operation, and increased service life. All parts can be bought at Ford dealers for less than $60 including the fluid.

A 20,000+ GVW cooler is highly recommended for all vehicles. Breakdown of the transmission fluid often results in "converter shudder" (feels like driving over rumble strips) where converter tries to maintain a steady slip rate during lock-up, but alternates between slipping and grabbing. Frequent fluid changes, especially when used for towing, are the single best method to prevent shudder. Shudder occurs because the torque converter never fully enters "lock-up", and ends up bouncing in and out of lock-up to slip. This causes the engine to flare up and then down again as the clutch cannot hold back the power of the engine.

4R7xx Usage

2002

4R70W used in all applications:

2003

4R75W Used in:
4R70W usage in trucks:
4R70W usage in cars:

2004

4R75E used in:
4R70E used in:
  • 4.6 L Triton F150(except F150 Heritage)
4R75W used in:
4R70W used in all other applications:

2005

4R75E used in 5.4 L V8 2-valve and 3-valve trucks:
4R70W used in:
4R70E used in:

2006 to 2008

4R70W used in:
4R75W used in all applications:

See also

LINCOLNSONLINE.COM

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