The 1973 OPEC oil embargo had a massive impact on the auto industry. In short order, fuel economy suddenly moved to the forefront of deciding factors for new car shoppers. While fuel prices started to level out in later 70s, it had enough impact to change the American auto industry to focus on more fuel-efficient vehicles. Some of this was forced on them through the US Government passing the Energy and Conservation Act which introduced CAFE regulations that came into force for the 1978 model year. Ultimately though, when fuel prices spiked again due to the 1979 Oil Shock, it became clear that the enormous V8 gas guzzling dinosaurs of the early and mid-1970s were headed for permanent extinction.
To help improve fuel economy, initially automakers used band-aid solutions, such as very steep rear axle ratios, to increase fuel economy. As time went on, newer more efficient American cars were designed that focused on being smaller and lighter. Cars such as the GM’s 1977 B-body or Ford’s 1978 Fox bodies were radical departures from the past and offered significant improvements in fuel efficiency. During this time, engineers were looking at all areas of a vehicle to increase fuel economy, including things like low drag brakes, low rolling resistant tires, aerodynamics, and more efficient transmissions with less rotating mass and lockup torque converters.
When it came to automatic transmissions, the standard formula from the 1960s to the late 1970s was a three-speed automatic with a non-lockup torque converter. While there were some efficiencies gained with newer light weight transmissions, like GMs ill-fated TH200, ultimately what was really needed was an overdrive. Borg-Warner built an auxiliary mechanical overdrive for manual transmissions which was first offered by Chrysler in the mid-1930s. In the 1940s and 1950s other manufactures also offered these auxiliary overdrive units for manual transmissions. As fuel prices dropped, engines became more powerful and the automatic transmission became the primary choice of Americans, the overdrive option faded into the past during the 1960s for the most part.
Performance was the big seller for Ford in the 1960s, not fuel economy.
It was during the 1960s that Ford had started to experiment with an overdrive equipped automatic transmission called the XT-LOD (Extension Lockup Overdrive). Ford envisioned an automatic transmission that featured split torque power delivery to help improve efficiency. However, the relatively low fuel prices meant that Ford ultimately decided that there would be little interest from the public. The project was shelved around 1966 until the oil embargo in late 1973 brought the project back to life.
Development continued through the 1970s for a 1980 model year release. The newly developed transmission was called FIOD (Ford Integrated Overdrive), however, it was renamed AOD (Automatic OverDrive) once it was released to the marketplace in late 1979. The AOD was considerably larger and heavier than Ford’s smaller C-4. It weighed in approximately 195 lbs with a torque converter, which was comparable to the heavy-duty C-6. It was also fairly close in width to C-6, but a bit shorter in length being about the same length as the smaller C4 and FMX. This meant an AOD could be utilized in most RWD Fords that used one of the aforementioned older transmissions.
This video shows a Simpson gearset. It only allows for three forward speeds.
At that time, Ford’s most commonly used modern transmissions were the C-4 and C-6. Both of these were 3-speed automatics that used the Simpson gearset as their basis. This was also the case with many torque converter equipped three-speed automatics of that era, including the Torqueflite 727 and the Turbo Hydramatic 350/400. While the Simpson gearset has some advantages like simplicity of design, compact size and ease of manufacture, it is limited to only 3 forward speeds. To add a 4th overdrive ratio, an additional gearset is required.
This video shows the Ravigneaux gearset. It allows for four forward speeds, one of which is overdrive.
Although Ford had introduced its Simpson based transmissions in 1964 and 1966 respectively, it also introduced the FMX transmission in 1968. Rather than being a clean slate design like the C-4 and C-6, the FMX evolved from the MX/FX transmissions, which evolved from the old Borg-Warner based Cruise-O-Matic transmission. Even in 1968, the FMX seemed to be a somewhat old fashion stop gap that only really only existed to help with production shortages. It used a heavy cast iron case and continued to use the Ravigneaux gearset of its predecessors. While the Ravigneaux gearset was only used for 3 speeds in the FMX, this gearset could actually be reworked to have four forward speeds, one of which being overdrive. So, when Ford started the development work on a 4-speed overdrive transmission, using the familiar Ravigneaux gearset provide a simple and cheap solution.
AOD cutaway diagram
The Ravigneaux gearset used in the AOD had gears with the same tooth count as the FMX. This meant that the first three ratios of the two transmissions were identical. This gearset produced an overdrive ratio of 0.67:1, which was considerably steeper than most overdrives used on manual transmissions. Add-on external overdrives typically had ratios in the 0.7:1 to 0.82:1 range. The AOD overdrive was steep enough to reduce the final drive ratio of a 4.10:1 rear axle to 2.75:1! The reality of the times was Ford was seeking best fuel economy numbers possible, so this transmission used with far steeper rear axle ratios, typically in the 2.73:1 to 3.08:1 range. While this returned good EPA numbers, in the real world it made for some very over geared cars.
This diagram shows a typical electro-hydraulic torque converter lockup. It includes a mechanical clutch piston and a damper. The clutch is electrically controlled by a solenoid inside the transmission. The solenoid uses hydraulics within the transmission activate or de-activate the clutch.
In addition to the overdrive, Ford engineers used other design improvements in the AOD to improve efficiency. Torque converters are very good at multiplying torque at low speeds, but are not overly efficient at high-speed cruise; some torque converters can slip as much as 10% at highway speeds. During the late 1970s and early 1980s, manufacturers started to add electro-mechanical torque converter lockup clutches. When the torque converter was locked-up, there was effectively a direct mechanical connection from the engine to the transmission eliminating all torque converter slippage.
The photo shows the two input shafts used on the AOD. The small shaft is for the direct connection to the engine which provides the “lock-up” and the medium size shaft provides input from the torque converter. The top photo shows the damper assembly.
Ford incorporated a lockup mechanism in the AOD, but it didn’t used the electro-hydraulically activated clutch mechanism like most other transmissions. It used a more unusual solution that was undoubtedly also cheaper. Instead of a lockup clutch, the AOD “lockup” was direct drive connection to the engine that bypassed the torque converter. To make this work the AOD had dual input shafts. One input shaft was connected to the torque converter turbine, while the other was a direct mechanical connection to the engine flexplate. Since there is no cushioning effect from the torque converter with the direct drive mechanical connection, Ford engineers incorporated a damper to help reduce noise and vibration. The transmission could use either the input from the torque converter, the direct drive connection, or a combination of both.
So how did exactly did this function? In the first two speeds, the transmission operates using the input shaft connected to the torque converter turbine. This allows for torque multiplication under acceleration, just like the other non-lockup transmissions. Once the transmission shifts into third, things get a little more complicated. Here the transmission input is split between the two input shafts, hence the split torque name. Approximately 60% of the input to the transmission comes from the direct drive connection, while the remaining 40% comes from the torque converter turbine. The method by which this is achieved is explained in great detail on Ate Up With Motor’s article.
The end result is third gear in the AOD does not have a true lockup, but the split torque input significantly reduces the torque converter slippage, increasing efficiency. The disadvantage was that if the driver wanted heavy to moderate acceleration in the third gear there was minimal torque multiplication available.
When the AOD shifted into 4th gear, the input was solely made by the direct mechanical connection to the engine. This was the AOD’s “lockup.” The reality was that it was just simply completely bypassing the torque converter in 4th gear. Like the third gear, this methodology worked but came at a disadvantage. The AOD generally upshifted from third to fourth around 40 mph to maximize fuel economy.
Unlike other overdrive transmissions with a lockup clutch mechanism, the transmission had no ability to run the torque converter unlocked in overdrive. So, when accelerating and the transmission shifts from third to fourth, the AOD tended to lug the engine as it immediately went into overdrive with full lock-up. Competitors transmissions would shift into 4th with the torque converter unlocked which reduced the RPM drop and would typically only lock-up once the driver have settled into a cruise.
Furthermore, if the driver needed moderate to heavy acceleration while in overdrive, the engine would lug down since the converter could not unlock. Once enough throttle input was used, a downshift to third would occur with a significant RPM gain. In comparison, most other 4-speed overdrive transmissions would unlock their torque converter first. This would increase engine RPM and performance through the additional torque multiplication; it almost acted like having an additional gear between third and fourth. If further power was requested, the transmission would downshift to third, but with the torque converter unlocked the RPM change would not be as dramatic as the AOD.
This two diagrams show the two methods by which the AOD controlled its part throttle shifts. Some applications used a TV rod (bottom) and some used a TV cable (top).
Ford engineers also adopted a different method to control the transmissions shifts with the AOD. Unlike previous Ford transmission which utilized a vacuum modulator and a kickdown rod to control the part throttle shifts, the AOD adopted a throttle valve cable (TV cable) or rod. Ford elected to use the TV Cable due to the inadequate vacuum signal in overdrive and less sensitivity to operating at different altitudes. This cable was connected directly the throttle and the transmission utilized this input to determine not only the shift speeds, but also the transmission line pressure. Thus, adjustment of the TV cable was critical to proper transmission operation and an improperly adjusted cable could lead to transmission failure. Ford also designed the valve body on the AOD to permit manual selection of only three of the four speeds. Gear selectors for AODs read OD-3-1, with no 2nd gear selection available.
The 1980 Lincoln Continental Mark VI boasted a 41% improvement in fuel economy from 1979 models. The AOD transmission was a big part of this improved economy.
In the fall of 1979 Ford introduced the AOD transmission to the marketplace making it the first automatic overdrive transmission introduced by an American manufacturer. It was standard equipment in the all-new downsized 1980 Lincoln Continental and Mark VI. It was available optional equipment on Ford’s LTD and Thunderbird as well as Mercury’s Marquis and Cougar. The big advantage of the AOD was the significant boost in fuel economy, but AOD equipped cars also had numerically higher rear axle ratios which helped to increase acceleration. The 1980 Ford LTD used a 2.29:1 rear axle ratio with a 3-speed automatic, but used a 3.08:1 rear axle ratio with the AOD. Ford claimed the AOD provided a 1.5 mpg boost to the overall EPA rating and a 4-mpg improvement in highway use along with an approximate 1 second 0-60 improvement.
GM did not release its first automatic overdrive transmission until 1981.
Ford having used the Ravigneaux gearset continuously through the late 1970s certainly gave it a leg up on developing a new overdrive transmission. In comparison, GM’s first overdrive transmission was the TH200-4R, which was introduced a year after Ford. GM’s TH200-4R transmission used a more complex design which likely cost more to develop. Unlike the AOD, the TH200-4R utilized a conventional electro-mechanical torque converter lockup clutch. It also used a Simpson gearset which meant it required an added overdrive carrier/single gearset to add the 4th overdrive ratio. GM also developed the clean slate TH700-R4 overdrive transmission, which used a unique Simpson split-compound gearset, but it wasn’t released until 1982.
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Automatic Comparison Chart |
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| Name | Manufacturer | Gearset | 1st Gear | 2nd Gear | 3rd Gear | 4th Gear | Reverse |
| C4/C6 | Ford | Simpson | 2.46:1 | 1.46:1 | 1:1 | n/a | 2.18:1 |
| FMX | Ford | Ravigneaux | 2.40:1 | 1.47:1 | 1:1 | n/a | 2.00:1 |
| AOD | Ford | Ravigneaux | 2.40:1 | 1.47:1 | 1:1 | 0.67:1 | 2.00:1 |
| 4R70W | Ford | Ravigneaux | 2.84:1 | 1.55:1 | 1:1 | 0.70:1 | 2.32:1 |
| E4OD | Ford | Simpson + extra OD gearset | 2.71:1 | 1.54:1 | 1:1 | 0.71:1 | 2.18:1 |
| TH350 | GM | Simpson | 2.52:1 | 1.52:1 | 1:1 | n/a | 2.07:1 |
| TH400 | GM | Simpson | 2.48:1 | 1.48:1 | 1:1 | n/a | 2.07:1 |
| TH200 | GM | Simpson | 2.74:1 | 1.57:1 | 1:1 | n/a | 2.07:1 |
| TH200-4R | GM | Simpson + extra OD gearset | 2.74:1 | 1.57:1 | 1:1 | 0.67:1 | 2.07:1 |
| TH700-R4 | GM | Simpson split compound | 3.06:1 | 1.63:1 | 1:1 | 0.70:1 | 2.29:1 |
| TF 727 | Chrysler | Simpson | 2.45:1 | 1:45:1 | 1:1 | n/a | 2.20:1 |
Despite the fact that they all used different design concepts, the AOD, TH200-4R and TH700-R4 automatics all had significant teething problems that lead to unreliability for the earliest iterations. The AOD was continuously improved throughout the 1980s until it became a reasonably reliable transmission. Ford’s engines improved during this time too, which made the shortcomings of the AODs split torque operation less obtrusive. The AOD was utilized in many RWD Ford cars, including the Panther and Fox platform cars, and also was utilized in light duty trucks and vans.
To strengthen the AOD for performance applications, transmission builders will replace the original two piece AOD input shaft (left) with a solid one piece input shaft (right). This greatly increases the strength but removes any ability to have torque converter lock-up.
For the 1992 model year, Ford introduced the AOD’s replacement, the AOD-E. The AOD-E was an updated version of the AOD, utilizing an electronically controlled valve body and a conventional electro-mechanical lockup clutch mechanism. This meant that the dual input shafts were gone and the AOD-E used a conventional single input shaft. The AOD was phased out of production after the 1993 model year. The AOD-E was eventually updated to the 4R70-W which use a revised Ravigneaux gearset. This new gearset created lower 1st and end gear ratios (2.84:1 first and 1.55:1 second) but a slightly higher overdrive ratio of 0.70:1. This wider ratio spread was better suited to the modular V8 engine’s power band.
Lentech specializes in performance AOD transmissions which can withstand very high horsepower applications. This particular transmission has a custom bell housing installed to allow it to be utilized with Ford FE engines.
Today, the AOD is often not remembered fondly, as is commonly reiterated on Curbside in the comment section. The AODs primary goal was fuel economy improvement, but it was used in some performance applications such has the high-output 5.0 Mustangs. That said, most enthusiasts of that time preferred the 5-speed manual due to the significant performance disadvantage of the AOD.
Ironically today, the AOD has received a bit of a reprieve in the aftermarket performance world. While in stock form they are not particularly strong or well suited for performance applications, an AOD can be built to be very strong good performance transmission with modern aftermarket parts. The strongest aftermarket versions eliminate the weak dual input shafts, split torque and lockup mechanism, making it a 4-speed non-lockup OD transmission. Specially built high performance AOD transmissions are even sometimes used in non-Ford applications, which is something that doesn’t happen with Ford’s other transmissions. There may not be too many of the 1980s Fords originally equipped AODs likely to become collector cars. But with overdrive swaps into old American cars being an ever-popular upgrade, I expect that many AODs will live on for a long time yet.
Here here.simply great article with history context tech etc. I have mentioned in a few posts that 20 years ago I swapped a 1990 mustang GT motor into an 84 crown Vic, Also installed some suspension bits as well as more than a few curse words. Upon getting the motor fully in and running I took it out for a test drive completely ignorant of the throttle position cables importance . Reminds me of a Steven Wrightline: “ you know when they say you shouldn’t put metal in a microwave? Well, they’re right.” I smoked that transmission in maybe 30 minutes of driving. I did get a very clean used one for a number I can’t remember but I remember it wasn’t horrible. I also said what the hell and picked up a first level shift kit for the unit. Now looking back on it don’t know if I needed the shift kit as frankly I wasn’t looking to cut my acceleration times or anything but it was fun to have done it just put a little edge on the shift. Getting back to the AOD I had never noticed or thought to notice that fourth was a full lock up all the time although in subsequent purchases including my Mazda MPV 2004, it was clear that in fifth gear it would unlock the converter. My crown Vic with the HO302 never felt wanting at highway speeds but certainly it would’ve benefited from the unlock. And that’s the last note I think my car had a 308 rear axle which resulted in Tire spinning capability in first gear As well as 2000 RPM at 80 miles an hour
Around 2014 my kid had an 89 Grand Marquis and I did a bunch of reading on the AOD. The forums were full of stories about how critical that TV cable was. If they had been left alone they were usually pretty reliable, but if they had been fooled with during other engine work, a plastic grommet could disintegrate and lead to catastrophic failure. At that time, it was said that new TV cables from Ford had been discontinued and were becoming scarce.
Before he bought his Grand Marquis, he and I looked at a Crown Vic of about the same age. It was a really sweet low mile car that had been driven about 100 miles from where an elderly relative had lived. The car would not shift into 4th and I pulled the dipstick and smelled the burned fluid. These experiences gave me all the more reasons to despise that miserable lump of a transmission. Well, that and the fact that the one in the Grand Marquis started slipping badly and led to the car being sold for a significant loss.
Thank you for this wonderful article on a transmission I knew little about. I have rebuilt my share of C4 and C6s (they are easy) but these managed to escape me.
This fills a big hole here at CC and is a really helpful guide to these early OD automatics and why they felt so different from the driver’s seat.
This answers one questions I have had for a long time – the difference between the AOD and the AOD-E. And the E4OD, for that matter. I owned one of each and knew instinctively that the newer versions were far more than a simple electronic shifting control applied to the basic AOD. This confirms that the lockup mechanism on the newer versions was entirely different, which again confirms my seat of the pants analysis.
One other reason the 5 speed Mustang GTs were favored over the automatics is that the engines on AOD cars were detuned. Going from memory, the AOD cars got 175 hp while the manual transmission cars were in the neighborhood of 210. I recall reading that the hp reduction was to protect the fragile transmission.
The detuned 5.0 was used in AOD-equipped Mustangs through ’85; after that, the engine was the same as used in the 5-speed. My dad still has an ’88 Mustang 5.0 with an AOD, and it’s a dog compared to 5-speed models (which we test drove back in the day). With a 2.73 axle, you’re almost forced to drive around town in direct drive. Plus, the anecdotes about the TV cable are no joke. My cousin bought our ’87 T-Bird (over 20 years ago now) and the bushing broke at the throttle body. He took it to a transmission shop that “test drove” it to “see what was wrong.” They smoked the transmission so badly that it killed the engine when we dropped it into gear, and I got to help him replace the transmission in my uncle’s driveway.
Anyway, I drove many miles in AOD-equipped vehicles, and share many others’ opinion that it was a sluggish-feeling transmission. Vince, you did an excellent job explaining why that is (as did “Ate Up with Motor” over at his website). I hadn’t thought about that split “input shaft” in years, and I never put much effort into understanding why they designed them that way.
Thank you both for the comments. As Aaron already pointed out, I referring was to the majority of 5.0L Mustangs from 1986-1993, which had the same power rating for both auto and manual. I have some contemporary tests for late 80’s 5.0L Mustangs. An AOD equipped Mustangs is over 1 second slower through the 1/4 mile than a 5-speed. That said, not all is equal in the tests, and the AOD cars typically have steeper rear gears and were convertibles, but the performance drop was significant.
Hey, my then-girlfriend’s LX 5.0 convertible may have had an automatic but was CONSIDERABLY more lively and enjoyable than my own Iron Puke ’87 Grand Am LE.
That’s true, but a five-speed car would have been significantly livelier than your girlfriend’s car. 🙂
Thanks for this. I’ve gotten the broad strokes before, but this puts it all together. I seem to have missed out on the joys of driving an AOD-equipped Ford, but I seem to remember riding in one or two and noting its ill-suited manners: chugging along in way too high a gear.
Automatics are fascinating, given the many ways to make them work. But evolution selects the winners, and that favored the four speed with lock-up clutches. My first drive in an early Ultradrive 4-speed Caravan was a bit of a revelation, noting its subtle rpm drops/increases as the TC locked/unlocked on the freeway. And it did everything so smoothly.
I am glad you enjoyed the article. Lock-up torque converters are such a simple solution to increasing transmission efficiency. The early lockups were fairly noticeable, as they basically were an on-off switch. However, since then, torque converter clutch modulation, or pulse width modulation, has allowed a TCC to be applied with controlled slippage making it barely perceptible.
If you think about it, the “4-speed with lock-up torque converter” is essentially an original 1939 Hydramatic with a 1949 Packard Ultramatic Lock-up Torque Converter.
It really isn’t — it’s much closer to being a ’50s Borg-Warner DG transmission with an extra gear.
If I understand correctly, the Borg-Warner DG locks up the torque converter at the same time it shifts into high gear. On the other hand, the Packard Ultramatic clutch lived inside the torque converter, which allowed it to be engaged/disengaged separately from any gear shifts. So you could actually lock-up the torque converter in low gear, and “kick-down” would happen first simply from disengaging the torque-converter lockup. The Packard mechanism is fundamentally the same (including the hydraulic coupling passageway through the shaft) as the diagram for the AOD above. So, apart from the Hydramatic using a different gearset than later transmissions, I think the analogy still applies.
My apologies, I thought you were arguing that the AOD was like a mating of Hydra-Matic and Ultramatic, rather than other four-speed lockup automatics. Yes, the Ultramatic lockup clutch was generally similar to later lockup converters in principle, and the late Twin Ultramatic more so in that it would shift to high and then lock the converter.
That said, Hydra-Matic bears little resemblance to modern four-speed automatics. It didn’t have an overdrive gear, and it would have taken some elaborate contrivance to get one with the original layout. Its gearing was similar to a later Simpson gearset three-speed (although it was neither Simpson nor Ravigneaux) with an extra low first gear, since it didn’t have a torque converter. With the dual-coupling Hydra-Matic, Engineering Staff did consider adding a lockup clutch (since there was more slippage in fourth than with the single-coupling transmission), but apparently decided the split torque layout was good enough.
Excellent article that explains why these were so miserable drive, at least here in mountainous BC where frequent engine load changes combined with gutless engines made these constantly cycle from 3-4 . I usually left the selector in “3” under these conditions.
It actually felt somewhat like Chevy’s old Powerglide if you left it in “OD”! It was certainly a better effort than GM’s early biodegradable OD automatics though.
Thank you! Yes these over geared AOD cars were not overly well behaved in mountainous terrain. Even in hilly country where I live, they weren’t the best behaved, not being able to pull a decent grade without downshifting. I don’t know if I necessarily agree that the GM ODs were a worst effort than the AOD. They each have their inherent weaknesses, but I wouldn’t say one was better than the other.
Still have the ’88 Mercury Grand Marquis Colony Park I ordered for my wife. Selected the Class III Trailer Tow package. It included true dual exhausts increasing power and torque by 10 horsepower and 10 ft/lbs respectively along with external transmission and power steering oil coolers and of interest to this discussion a 3.55 to 1 rear axle ratio with Traction-Lok which necessitated the inclusion of a full size spare tire on a 5th turbine spoke cast aluminum wheel.
This makes all the difference in the world with how these cars drive. Acceleration and throttle response are quite adequate. Took annual summer weeks long road trips all over the country often driving 900 to 1000 miles only stopping for gas and to eat. Currently has 140,000 miles with the same engine and transmission and no major repairs.
I did get a recall notice early on to replace the throttle valve rod bushing from a synthetic material to brass because the synthetic one would deteriorate and destroy the transmission as described.
Nice write up. I remember something about the AOD being a derivative of the FMX design. I have installed these in project cars along with C4 and C6. Indeed they are heavy like a C6. I had one I bought from a gent, an AODominator. A+ servo, and Kevlar bands. Great tranny, and like any automatic, they last if you keep them from getting super hot. Since the AOD only had three quadrants, in order to hold 2nd, you shift back into first. The AODE solved that by having an electronic activation for OD.
Yes, you could use that method to get second gear, but it’s just a ridiculous this was the only method. The average Joe certainly didn’t know this and probably would be hesitant to try this brutal method. Bottom line it was a cost cutting measure.
Lentech offers new valve bodies that allow for manual second gear with OD controlled by an electric switch. It changes the shift quadrant from 4-3-1 to 3-2-1 and OD is selected by a switch.
The 1-D-1 dance is in the owner’s manual and there isn’t anything brutal about it. Though I can see someone being hesitant to try it or downshifting into “1” at higher speeds which is also acceptable since it doesn’t go directly to 1st unless the speed is low enough.
When doing the 1-D-1 shuffle at WOT it causes damage to the transmission (the direct clutch and OD band). That is one reason why Lentech made their new AOD valve body years ago for those interested in performance driving.
While this procedure was the owners manual, how many read and knew this procedure?
Very interesting article – I hadn’t given much thought to this transmission’s long history even though we have a ’95 Thunderbird. In our car’s case, I’ve been generally satisfied with the AOD’s (or AOD-E’s, I suppose) drivability; it seems to be a good match for the 4.6 V-8 – that engine’s flexibility probably does compensate for some of the transmission’s shortcomings.
Oddly, just last month the transmission quit shifting into overdrive. It spent quite some time at the transmission shop, and they determined the problem was with the PCM… they replaced the PCM and it now shifts fine, but I have a suspicion that some other electrical problem is going on with the car. I hope I’m wrong, and that the transmission continues to shift smoothly for years to come.
Going from an AOD to an AOD-E is like going from a 19 inch black and white TV to a 50 inch HD color set. The difference in driving enjoyment is that kind of jump. I agree that the AOD-E was really well matched with the 4.6.
Thanks Eric! As JP pointed out, the AOD-E was a big improvement over the AOD and I’d argue the 4R70W with the wider ratio spread was better yet. I thought the 4R70W teamed with a 4.6L and a gear ratio of 3.27 was about the sweet spot for these powertrains (at least in the cars).
The only point I want to add is that the use of a TV linkage was sort of a retrograde step. Most all early automatics capable of shifting for themselves used a TV linkage (either connected to the accelerator pedal or the actual throttle) to signal load. Some transmissions had vacuum modulators, but they only served to vary the force applied to the clutches and brakes.
In the early sixties, there was a shift to using the vacuum modulator instead of a TV linkage — Turbo Hydra-Matic and Super Turbine 300 did this, and many other manufacturers followed suit. The advantage this offered is that it allowed shift points to be more closely tailored to actual torque demand, and it could also be tailored to automatically adjust for atmospheric pressure differences (so, automatic altitude adjustment). It also wasn’t so subject to adjustment problems — any time you have a long, convoluted system of cables and/or rods to connect moving parts, there are many ways it can become misaligned or too tight or too loose.
However, with the AOD, Ford found that its emissions-controlled engines turning over at sleepy engine speeds in overdrive didn’t produce a strong enough vacuum signal for the modulator to work properly. So, they went back to the TV linkage instead.
Thanks for mentioning the rationale behind the TV cable usage. I forgot to put that into the article. The Ford engineers claimed it was due to the inadequate vacuum signal in OD and less sensitivity to engine vagrancies at various altitudes. I amended the text accordingly.
That said, the TV cable was utilized by competitors OD transmissions as well, likely for the same reasons, I should also clarify that the engines of this era didn’t have an issue producing vacuum, if anything, most had strong vacuum due their mild camshafts. However, the RPM operating range was so low in OD, the variances in vacuum signal with throttle movement was not adequate enough for the vacuum modulator. Ultimately the solution was a electronically controlled transmission.
Who-all? Ford, perhaps, but Chrysler’s Torqueflites never used vacuum modulators; they used TV linkage right on through, well up into the late ’90s and perhaps beyond.
Would love to hear more about the Ford AXOD. Had one car with that and one with the AOD.
When I see one of Vince’s articles, I drop everything to read it. I am 100% for sure going to learn something.
AOD was about the worst automatic transmission I have ever experienced. Like Vince mentions in his piece, there was no staged converter unlock. In other auto o/d units of the era, first the clutch would unlock and then there would be a downshift.
With AOD, the converter did not unlock. When in fourth gear, a quick stab at the throttle would result in a stumble and a jerky downshift. It was not a pleasant experience.
Thanks Len, I appreciate the compliment!
I had a 84 T-Bird, 302 with the AOD. Fuel mileage was much better on the highway that my 78 Futura, 302 C4. My Bird did have the 3.08 rear axle so it had decent acceleration. It also had the 2 barrel throttle body fuel injection which was also a big improvement over the 2 barrel carb on the Futura. Both cars were good cars for me.
The AOD was a bit funky on the shifts but never had to worry about lock up converter shutter. I was working for GMC at the time the 700R4 came out, what a pile of crap that thing was. Then put that gutless broken 6.2L diesel in front of it and you really had a turd.
I have bìtched about this before in re the made-up babble on the subject in the owner’s manual of my folks’ Stinkoln Clown Car: “There is no ‘2’ position because the quadrant has only six positions. Therefore, the second-gear starts described elsewhere in this manual are not available”. Uh…thanks? (And OBTW, second-gear starts weren’t mentioned anywhere else in the manual).
Meanwhile, those showoffs over at GM, in a lavishly-financed skunkworks R&D program, somehow managed to figure out how to pull off the epic tour de force of—wait for it—adding a seventh position (I know, right?) to arrive at P R N 🄳 D 2 1 for the TH700R4 and TH2004R.
(I say that, but I’m just guessing. Perhaps there was something about the AOD that would’ve made providing a ‘2’ position difficult or costly. Or maybe Ford were just being cheap and saving on dashboard parts.)