FORD’S SPLIT TORQUE AUTOMATICS
During this period, Ford also revived the split torque concept, first for the AOD, Ford’s first four-speed overdrive automatic, and then for the ATX, the company’s first automatic transaxle for front-wheel-drive applications.
AUTOMATIC OVERDRIVE TRANSMISSION (AOD)
The Automatic Overdrive (AOD) transmission, introduced for some full-size FoMoCo cars in the 1980 model year, was derived from Ford’s older three-speed FMX automatic. It used a Ravigneaux compound gearset with three long and three short planet pinions on a common planet carrier, two sun gears (one with 36 teeth, the other with 30), and a single annulus (with 72 teeth) affixed to the output shaft.
As in the FMX, the torque converter turbine drove the smaller rear sun gear in first, second, and third gears. Two one-way clutches (supplemented in Low by a brake band) could alternately hold the carrier or the larger front sun gear, providing two forward reduction ratios. Where the AOD parted ways with the FMX was in the direct drive third gear. Instead of locking the front sun gear to the input shaft in high, as the FMX did, the AOD used an additional direct clutch to lock the planet carrier to a central shaft that passed through the main input shaft and was driven directly by the engine.
In third, engine torque was split between the rear sun gear, which rotated at turbine speed, and the planet carrier, which rotated at engine speed. Because the carrier always rotated faster than the rear sun gear, the long planets overdrove the larger front sun gear. This forced the short planet pinions to resolve the speed difference and drive the annulus forward at a speed slower than the carrier, but faster than the rear sun gear, demultiplying hydraulic slippage by 58.3%. (We’ll spare you the math, which with Ravigneaux gearsets is very cumbersome.) For example, if the engine was turning 2,000 rpm and converter slippage was 100 rpm, the annulus would rotate at 1,958.3 rpm, reducing net hydraulic slip from 5% at the turbine to 2.1% at the output shaft.
The AOD’s new overdrive fourth gear was created by releasing the forward clutch — thereby disconnecting the rear sun gear from the main input shaft and the turbine — while engaging a brake band to hold the front sun gear stationary. With the direct clutch still engaged, the carrier, rotating at engine speed, overdrove the rear sun gear, forcing the annulus to rotate at 1.5 times engine speed — an ratio of 0.67:1. The torque converter turbine continued to rotate in fourth, but was no longer connected to the planetary gears, so there was no hydraulic slippage. This lockup wasn’t available in any of the lower gears.
Ford took a different approach with the ATX transaxle, which became optional on the new FWD (Mk3) Ford Escort and Mercury Lynx for 1981 and the Ford Tempo/Mercury Topaz for 1984. Unlike the AOD and the earlier GM split torque transmissions, the early ATX used a separate planetary gearset specifically for torque-splitting purposes.
Known in Ford parlance as a “splitter gear,” the additional gearset was located within the torque converter torus housing, between the turbine and the flex plate. It was a simple planetary gearset with a single annulus (with 78 teeth) and three planet pinions surrounding a sun gear with 48 teeth. The flex plate and torus housing drove the splitter unit annulus at engine speed while the transmission input shaft, driven by the turbine, drove the splitter sun gear.
As we’ve explained in the preceding pages, this arrangement served to demultiply hydraulic slippage in the torque converter. Since annulus speed (VA) was engine speed while sun gear speed (VS) was turbine speed, the speed of the splitter gearset’s planet carrier (VC) was therefore:
VC = VS + ((VA – VS) / (1 + sun gear teeth / annulus teeth))
VC = VS + ((VA – VS) / 1.615)
For example, if the engine were turning 2,000 rpm and there was 100 rpm of converter slippage, carrier speed would be 1,961.9 rpm, demultiplying hydraulic slippage from 5% at the turbine to about 1.9% at the carrier.
The splitter gearset’s planet carrier drove a hollow sleeve shaft (which for reference we’ll call the “splitter shaft”), passing through the main transmission input shaft. (The sleeve shaft was also hollow because it contained the solid driveshaft for the transmission oil pump, which was located on the opposite side of the transaxle from the torque converter.) Both input shafts carried power to the main planetary transmission, a Ravigneaux gearset with a single annulus (with 86 teeth), two sun gears (one with 52 teeth, the other with 29), and three short and three long planets (each with 17 teeth) on a common carrier. The carrier drove the differential input gears.
The splitter shaft was ineffective in first and reverse, rotating idly while the main shaft drove the smaller input sun gear at turbine speed. In second gear, the multi-disc intermediate clutch engaged to connect the splitter shaft to the annulus of the Ravigneaux gearset. Since the larger rear sun gear was held by a brake band, this caused the smaller sun gear to overrun the input shaft and spin idly on its one-way clutch. Since the splitter shaft was now driving, hydraulic slippage was demultiplied by 61.9% (1 / 1.615).
In the direct drive third gear, the multi-disc direct clutch engaged, again allowing the main input shaft to drive the smaller sun gear, and the brake band was released, allowing the large sun gear to rotate freely. The intermediate clutch remained engaged, so the splitter shaft continued to drive the annulus at the same time. With both the annulus and small sun gear driving, the planet gears overdrove the large sun gear, forcing it to rotate faster than the engine. This in turn forced the planet carrier to rotate faster than either input shaft, albeit still slightly slower than the engine.
Although the math is again very cumbersome, this arrangement demultiplied converter slippage by a whopping 93.4% in third. For example, if engine speed were 2,000 rpm with 100 rpm of converter slippage, carrier speed (discounting mechanical losses) would be 1,993.4 rpm, reducing hydraulic slippage from 5% at the turbine to a mere 0.003% at the differential. That was efficient enough that the ATX could forgo a lockup clutch without a noticeable sacrifice in fuel economy, an important consideration for Ford’s cheapest U.S.-market models.
THE TRIUMPH OF ORTHODOXY
Ford’s split torque revival was relatively brief. Later versions of the ATX transaxle abandoned the splitter gear and dual input shafts for either a conventional hydraulic lockup (which Ford abbreviated FLC, for “full lockup clutch”) or, in some applications, a centrifugal lockup clutch (CLC) similar to that of the C5 transmission. The change coincided with the availability of more powerful engines in the Escort/Lynx and Tempo/Topaz lines, which suggests that the rationale may have been to facilitate increases in the transaxle’s torque capacity. (Tempo/Topaz versions of the ATX already had extra clutch plates in each multi-disc clutch.)
Similar concerns led to the elimination of the split torque feature of the four-speed AOD in the early nineties. The AOD was adequately strong for early eighties engines, but as power and torque increased throughout the decade, the secondary input shaft became a notable weak link. When the electronically controlled AOD-E debuted in 1991, it had only a single input shaft with no third-gear torque split. The same was true of the closely related 4R70 and 4R70W that replaced the AOD-E in 1993.
By then, all or nearly all domestic and most non-U.S. passenger car and light truck automatics had lockup clutches, most of them hydraulically operated and electronically controlled, differing only in minor details. The centrifugal lockup clutch eventually went the way of the split torque units, since its purely mechanical operation didn’t offer the fine-tuned control of electronically controlled electro-hydraulic clutches, whose operation can be better tailored to different operating conditions. For example, an electronically controlled clutch can be programmed to remain unlocked during warm-up or if either the engine or transmission is in danger of overheating, which a centrifugal clutch cannot.
This period of comparative orthodoxy — mostly four-speed overdrive automatics with electro-hydraulic lockup clutches — turned out to also be relatively brief. Subsequent automatic transmission design has diverged along several paths, including relatively conventional planetary transmissions with an ever-growing number of gears, at least three types of continuously variable transmissions, and dual-clutch semiautomatic transmissions. All these are beyond the scope of an article that is already considerably longer and more complicated than we originally intended, so we’ll just say that for automatics that have torque converters, computer-controlled lockup clutches are now the established norm and are likely to remain so.
As for split torque layouts, those have become common for hybrid electric vehicles, but that subject, like many others, will have to wait for another day.
NOTES ON SOURCES
Our sources for this article included “Autocar Road Tests No. 1424: Packard 200 De Luxe Touring Sedan,” The Autocar 9 March 1951, reprinted in Packard Gold Portfolio 1946–1958, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1988): 39–41; “Autocar Road Test 1908: Vauxhall Cresta Hydra-Matic 2,651 c.c.,” Autocar 11 January 1963: 58–62; “Autocar road tests 1814: Buick Special,” The Autocar 31 March 1961: 494–497; R. August, R. Kasuba, J.L. Frater, and A. Pintz, “Dynamics of Planetary Gear Trains,” NASA Contractor Report 3793 (Grant NAG3-186), June 1984; Automatic Transmission Service Group (ATSG), Update Handbook AODE, 4R70W, 4R70E, 4R75E (Miami, FL: Automatic Transmission Service Group, 2006); Cernil Bagci, “Efficient Methods for the Synthesis of Compound Planetary Differential Gear Trains for Multiple Speed Ratio Generation,” Gear Technology July/August 1990: 14–35; Roy Beardmore, “Epicyclic Gears,” Roymech, 20 January 2013, www.roymech. co.uk/Useful_Tables/Drive/ Epi_cyclic_gears.html, accessed 20 August 2017; Ray T. Bohacz, “Mechanical Marvels: Shiftless Driving: Oldsmobile introduces the fully automatic transmission,” Special Interest Autos #180 (November-December 2000): 54–56, and “Mechanical Marvels: Shiftless Pleasure: The 1956 General Motors Hydra-Matic Transmission,” Hemmings Classic Car #35 (August 2007): 68–71; Warren G. Bopp, assignor to Eaton Corporation, U.S. Patent No. 4,445,599, “Cooling Means for Torque Converter Bypass,” filed 27 October 1981, issued 1 May 1984; and U.S. Patent No. 4,496,034, “Viscous Coupling for Torque Converter Bypass,” filed 15 June 1982, issued 29 January 1985; August H. Borman, Jr.; Forrest R. Cheek; and Milton H. Scheiter, assignors to General Motors Corporation, U.S. Patent No. 3,048,055, “Controlled Coupling Automatic Transmissions,” filed 27 December 1954, issued 7 August 1962; August H. Borman Jr., Charles W. Cline, and Carl E. Shellman, assignors to General Motors Corporation, U.S. Patent No. 3,132,535, “Transmission,” filed 20 September 1960, issued 12 May 1964; Buick Motor Division of General Motors Corporation, 1961 Buick Special Service Manual BPS 1.51 (Flint, MI: Buick Division of General Motors Corporation, 1961); “Special: The Happy Medium-Size Car!!!” [brochure], 1962; “The New Special Size 1961 Buick Special” [brochure, ca. October 1960]; “The trim-size Buicks for ’63” [Special/Skylark brochure, ca. October 1962]; “Road & Track Road Test: Buick Special V-6,” Road & Track Vol. 11, No. 3 (November 1961), reprinted in Buick Performance Portfolio 1947-1962, pp. 124-127; the Cadillac & LaSalle Club Modified Chapter website (www.modifiedcadillac.org); Cadillac Motor Car Division of General Motors Corporation, “Cadillac data book ’56,” September 1955; “Car Life Road Test: Oldsmobile F-85,” Car Life Vol. 9, No. 4 (May 1961), reprinted in Oldsmobile Automobiles 1955-1963, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1989): 66–70; “Car Life Road Test: Oldsmobile 98 Holiday Sports Sedan,” Car Life Vol. 10, No. 3 (April 1962), reprinted in ibid, pp. 74-78; Bill Carroll, “Inside Pontiac’s Terrific Tempest!” Sports Cars Illustrated Vol. 6, No. 4 (October 1960)) and “Pontiac Tempest Road Research Report,” Sports Cars Illustrated Vol. 6, No. 9 (March 1961), both reprinted in Car and Driver on Pontiac 1961–1975, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1986): 5-16; Rich Ceppos, “’78 Chryslers—goodbye to big cars,” Popular Science Vol. 211 No. 4 (October 1977): 96–97; Chilton’s Guide to Automatic Transmission Repair: 1980–84 Domestic Cars & Light Trucks, eds. Kerry A. Freeman, Dean F. Morgantini, Richard J. Rivele Jr., and W. Calvin Settle Jr. (Radnor, PA: Chilton Book Company, 1988); Chilton’s Guide to Automatic Transmission Repair: 1984–89 Domestic Cars & Light Trucks, eds. Kerry A. Freeman, Peter M. Conti Jr., W. Calvin Settle Jr., et al (Radnor, PA: Chilton Book Company, 1990); Chilton’s Ford Escort and Mercury Lynx 1981-95 Repair Manual, ed. Jaffer A. Ahmad (Radnor, PA: Chilton Book Company, 1995); Chrysler Corporation, “Chrysler Flexes Its Muscles and Works on Its Waistline,” Popular Mechanics Vol. 146, No. 4 (October 1976): 94, 169–174; Chrysler-Plymouth Division, “Chrysler 1978: New Yorker/Newport” [brochure 81-005-8003], 15 August 1977; Harold E. Churchill and Woodrow A. Hasbany, assignors to Studebaker Corporation, U.S. Patent No. 2,597,921A, “Torque Converter and Lockup Means Therefor,” filed 31 May 1946, issued 27 May 1952; Julius A. Clauss, assignor to Borg-Warner Corporation, U.S. Patent No. 4,124,106, “Wedging Centrifugal Lock Up Clutch With Torque Limiter,” filed 28 December 1976, issued 7 November 1978; Csaba Csere, “Eighty-Two Special Report: Technical Highlights,” Car and Driver Vol. 27, No. 5 (November 1981): 47–53; “Ford Tempo (Preview Test),” Car and Driver Vol. 28, No. 9 (March 1983): 73–79; and “J-Car Engineering Analysis,” Car and Driver Vol. 26, No. 10 (April 1981): 39–43; Howard L. Croswhite, assignor to Ford Motor Company, U.S. Patent No. 4,226,123, “Non-Synchronous Four Speed Automatic Transmission with Overdrive,” filed 6 December 1978, issued 7 October 1980; “Detroit Listening Post,” Popular Mechanics Vol. 154, No. 1 (July 1980): 54; Detroit Transmission Division of General Motors Corporation, “Detroit Transmission Division Welcomes You to the Home of Hydra-Matic” [flyer, ca. 1958], via GM Heritage Center; the GM Heritage Archive (gmheritagecenter. com/ gm-heritage-archive/); DIY Ford: Do It Yourself Ford Projects (www.diyford.com); Jack R. Doidge and Victor C. Moore, assignors to General Motors Corporation, U.S. Patent No. 2,947,199, “Transmission,” filed 26 November 1957, issued 2 August 1960; Terry B. Dunham and Lawrence R. Gustin, The Buick: A Complete History (An Automobile Quarterly Magnificent Marque Book) (Kurtztown, PA: Automobile Quarterly, 1980); Jim Dunne, “A first from Ford: 4-speed automatic transmission with .667 overdrive,” Popular Science Vol. 215, No. 2 (August 1979): 74–75; and “Detroit Report,” Popular Science Vol. 223, No. 2 (August 1983): 14; Jim Dunne and Jan P. Norbye, Buick 1946-1978: The Classic Postwar Years, Second Ed. (Osceola, WI: MBI, Inc./Motorbooks International, 1993); David Edwards, Antique Automatic Transmission Parts, www.autotran.us; Kevin Elliott, “Automatic for the People,” Hot Rod, 14 September 2009, www.hotrod. com, accessed 9 June 2017; Jack Erjavec and Ken Pickerill, Today’s Technician: Automatic Transmissions and Transaxles Classroom Manual (Boston: Cengage Learning, 2015); Ken Fermoyle, “Buick, Olds, Pontiac Go Compact,” Popular Science Vol. 177, No. 4 (October 1960): 72–76, 244–246, and “Pontiac Tempest: Radical New Compact,” Popular Science Vol. 177, No. 3 (September 1960): 53–58; Alan R. Fisher, assignor to Ford Motor Company, U.S. Patent No. 4,398,436, “Multiple Ratio Transmission Having a Torque Splitter Input Gear with a Pocketed Carrier,” filed 7 April 1980, issued 16 August 1983; Walter Fisher, assignor to Borg-Warner Corporation, U.S. Patent No. 4,108,290, “Hydraulic Torque Converter Lock-Up Clutch,” filed 12 November 1976, issued 22 August 1978; Ford Division of Ford Motor Company, “1982 Ford Escort: Look out world here comes Ford” [brochure], August 1981; “1982 Ford Fairmont Futura” [brochure 012-Ann], August 1981; “1982 Ford Granada” [brochure], September 1981; and “1984 Ford Tempo” [brochure 021-Ann.], August 1983; “Fuel-Saving Lockup Torque Converter,” Popular Mechanics Vol. 148, No. 4 (October 1977): 160; Norman T. General and Po-Lung Liang, assignors to Ford Motor Company, U.S. Patent No. 3,275,108, “Damper for Torque Converter Lock-Up Clutch,” filed 23 October 1964, issued 27 September 1966; “Golden Anniversary Packard Models,” The Motor 6 July 1949, reprinted in Packard Gold Portfolio 1946–1958: 19–21; Philip G. Gott, Changing Gears: The Development of the Automotive Transmission (SAE Historical Series) (Warrendale, PA: Society of American Engineers, 1991); T. Grace, Automatic Transmission Service Guide (Union, NJ: Lincoln Technical Institute, September 1966); Ken Gross, “1942 Oldsmobile B-44,” Special Interest Autos #40 (May-July 1977), reprinted in The Hemmings Book of Oldsmobiles: driveReports from Hemmings Special Interest Autos magazine, eds. Terry Ehrich and Richard Lentinello (Bennington, VT: Hemmings Motor News, 2001): 20–24; John Gunnell, ed., Standard Catalog of American Cars 1946-1975 Revised 4th Edition (Iola, WI: Krause Publications, 2002); Gilbert K. Hause and Oliver K. Kelley, assignors to General Motors Corporation, U.S. Patent No. 3,062,074, “Multi-Phase Transmission,” filed 19 February 1958, issued 6 November 1962; Walter B. Herndon, assignor to General Motors Corporation, U.S. Patent No. 2,876,656, “Controlled Coupling Multistep Automatic Transmissions,” filed 23 November 1953, issued 10 March 1959; Walter B. Herndon and Howard E. Olsen, assignors to General Motors Corporations, U.S. Patent No. 3,141,354, “Transmission,” filed 8 March 1962, issued 21 July 1964; Robert Arthur Hoetger, James Albert Hagaman, and William Nortman, assignors to Chrysler Corporation, U.S. Patent No. 4,033,436, “Transmission and Torque Converter with Lock-Up Clutch,” filed 12 May 1975, issued 5 July 1977; Ari Holopainen, “Planetary Gears,” LUGNET News, 2005, www.lugnet. com/~3813/epicyclic, accessed 9 June 2017; Roger Huntington, “The Great Transmission Controversy: Coupling vs. Converter,” Car Life Vol. 10, No. 2 (March 1963): 18–21; “Hydra-Matic Dampens That Thump,” Popular Science Vol. 167, No. 5 (November 1955), pp. 119–121, 260; John Saxon Ivey, assignor to Borg-Warner Corporation, U.S. Patent No. 4,037,691, “Centrifugal Lock Up Clutch for Fluid Couplings,” filed 2 January 1976, issued 26 July 1977; John Saxon Ivey and Russell Earl Silberschlag, assignors to Borg-Warner Corporation, U.S. Patent No. 4,063,623, “Fluid Coupling with Centrifugal and Torque Responsive Lock Up Clutch,” filed 29 June 1976, issued 20 December 1977; Ed Jacobs, “Ford: a baby Continental, mid-size wagons, and tire-smoking muscle cars,” Popular Science Vol. 219, No. 4 (October 1981): 94–97; Robert C. Juvinall and Kurt M. Marshek, Machine Component Interrelationships, Fifth ed. (Hoboken, NJ: John Wiley and Sons, Ltd., 2011); Alexander L. Kapelevich, “Analysis and Optimization of Asymmetric Epicyclic Gears,” Gear Solutions Vol. 61, No. 7 (August 2016): 50–55; Oliver K. Kelley, assignor to General Motors Corporation, U.S. Patent No. 2,176,138, “Combination Fluid Turbo Clutch and Variable Speed Gearing,” filed 5 February 1937, issued 17 October 1939; U.S. Patent No. 2,211,233, “Fluid Flywheel Gearing Arrangement,” filed 10 April 1939, issued 13 August 1940; U.S. Patent No. 2,377,696, “Transmission Drive,” filed 15 December 1941, issued 5 June 1945; and U.S. Patent No. 3,030,823, “Transmission” filed 11 July 1957, issued 24 April 1962; Oliver K. Kelley and Gilbert K. Hause, assignors to General Motors Corporation, U.S. Patent No. 2,957,370, “Multi-Phase Torque Converter,” filed 11 July 1957, issued 25 October 1960; John D. Kelly, “1953 Hydramatic Transmission.xlsx” [spreadsheet] and emails to the author, 7 to 8 March and 27 April 2017; Oliver K. Kelley and William S. Wolfram, assignors to General Motors Corporation, “Rotary Hydraulic Torque Converter with Dynamic Braking,” filed 30 July 1949, issued 15 September 1953; Al Kidd, “’55 Olds Super 88,” Motor Trend Vol. 7, No. 5 (May 1955), reprinted in Oldsmobile Automobiles 1955-1963: 5–6, 55; Jeff Koch, “Ford AOD Transmissions – The Bulletproof AOD,” Hot Rod March 1999, www.hotrod. com; Ted Koopman, “Testing the Packard for 1952,” Speed Age July 1952, reprinted in Packard Gold Portfolio 1946–1958: 48–53; Le Club 404, “Peugeot 404 Production History,” Club Peugeot 404 North America, n.d., www.peugeot404na. com/production-history, accessed 28 July 2017; George E. Lemieux, Reginald T. Lewicki, and Julius A. Clauss, assignors to Ford Motor Company, U.S. Patent No. 4,638,686, “Transaxle for a Vehicle Driveline,” filed 26 March 1980, issued 27 January 1987; Allan S. Leonard, Ralph C. Bolz, and Lawrence D. Burcz, assignors to Ford Motor Company, U.S. Patent No. 4,347,765, “Multiple Ratio Overdrive Transmission,” filed 5 October 1979, issued 7 September 1982; Po-lung Liang and Alan R. Fisher, assignors to Ford Motor Company, U.S. Patent No. 4,408,501 A, “Multiple Ratio Torque Converter Transmission with Main Transmission Planetary Gearing and a Compound Torque Splitter Planetary Unit Between the Converter and the Multiple Ratio Gearing,” filed 21 May 1981, issued 11 October 1983; Forest R. McFarland, assignor to Packard Motor Car Company, U.S. Patent No. 2,689,029, filed 15 January 1949, divided 1 July 1950, issued 14 September 1954; and U.S. Patent No. 2,694,948, “Transmission,” filed 15 January 1949, issued 23 November 1954; Steve A. Mikel and Alfred P. Blomquist, assignors to Chrysler Corporation, U.S. Patent No. 4,289,048, “Lockup System for Torque Converter,” filed 11 September 1978, issued 15 September 1981; Herbert L. Misch and Carroll J. Lucia, assignors to Packard Motor Car Company, U.S. Patent No. 2,630,893, “Transmission,” filed 7 March 1950, issued 10 March 1953; Ed Mobley, “Controlled Coupling Hydramatic/Jetaway Automatic Rebuild,” Edscars, 2006, www.photopaige. com/ edscars/ 60caddy/ CaddyWebSitev2_files/ TrannyRebuild2.htm, accessed 20 April 2017; Victor C. Moore, assignor to General Motors Corporation, U.S. Patent No. 2,919,607, “Transmission,” filed 30 November 1956, issued 5 January 1960; Robert S. Mueller, assignor to Eaton Corporation, U.S. Patent No. 4,462,492, “Cooling Arrangement for a Viscous Coupling Utilized as a Torque Converter Bypass,” filed 11 August 1981, issued 31 July 1984; “New Cars Described: 1956 Pontiacs Have Latest Transmission,” The Autocar 18 November 1955, reprinted in reprinted in Pontiac Limited Edition Extra 1949-1960, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1999): 45; Karim Nice, “How Gears Work,” HowStuffWorks.com, 16 November 2000 science.howstuffworks. com/ transport/ engines-equipment/gear.htm, accessed 11 August 2016; Paul Niedermeyer, “Automotive History: Studebaker’s Automatic Drive (Borg Warner DG150/200/250) – Advanced, Efficient, But Too Expensive in the End,” Curbside Classic, 26 August 2016, www.curbsideclassic.com/ automotive-histories/ automotive-history-studebakers- automatic-drive-borg-warner-dg150200250- advanced-in-some-respects-not-so-in-others/, accessed 26 August 2016; James H. O’Brien, assignor to Packard Motor Car Company, U.S. Patent No. 2,640,572, “Lock-Up Clutch in Fluid Torque Converters,” filed 31 December 1947, issued 2 June 1953; the Old Car Brochures website (oldcarbrochures.org); the Old Car Manual Project (www.oldcarmanualproject.com); “Olds F-85: Another Rocket Hits the Road,” Popular Mechanics Vol. 114, No. 4 (October 1960): 100–102, 310; Packard Motor Car Company, “1950 Packard with Ultramatic Drive” [brochure], 1950; and Owner’s Operational Manual: Golden Anniversary Packard, 2nd ed. (Detroit: Packard Motor Car Co., 1949); “Packard’s Ultramatic Drive,” Product Engineering July 1949, reprinted in Packard Gold Portfolio 1946–1958: 22–24; “Peugeot 404 Automatique,” Road & Track Vol. 18, No. 4 (December 1966): 73; Stanley L. Pierce, Jr., assignor to Ford Motor Company, U.S. Patent No. 4,014,223, “Multiple ratio hydrokinetic split torque transmission,” filed 22 May 1975, issued 29 March 1977; John B. Polomski, assignor to Borg-Warner Corporation, Inc., U.S. Patent No. 2,720,124A, “Transmission,” filed 9 October 1950, issued 11 October 1955; Pontiac Motor Division of General Motors Corporation, 1957 Hydra-Matic Manual (with 1956 Appendix) (Pontiac, MI: Pontiac Motor Division, General Motors Corporation, March 1957); “Powerglide Planetary Low Gear Ratios,” TCI Auto, 2012, www.tciauto. com/ tc/pg-ratios/, accessed 12 June 2017; George Reid, Ford AOD Transmissions (North Branch, MN: CarTech, Inc., 2014); How to Rebuild and Modify Ford C4 and C6 Automatic Transmissions (Forest Lake, MN: CarTech Books, 2012); Hesham A. Roushdy and Daniel H. Hildebrand, assignors to Ford Motor Company, U.S. Patent No. 4,224,838, “Four Speed Ratio Automatic Transmission With Compact Gearing,” filed 6 December 1978, issued 30 September 1980; “Saturday Mechanic Looks at the ’82 Fords,” Popular Mechanics Vol. 156, No. 4 (October 1981): 128–129, 169–170; Otto Schwab and Siegfried Krauss, assignors to Zahnradfabrik Friedrichshafen AG, German Patent No. 1,160,257B, “A Fluidic Torque Converter Arrange in Its Core Area Centrifugal Friction Clutch,” filed 20 August 1960, issued 27 December 1963; Senate and House of Representatives of the United States of America in Congress assembled, “Energy Policy and Conservation Act,” Public Law 94–163, Title V (Part A – Improving Automotive Fuel Economy), 22 Dec. 1975; Mort Shultz, “Car Clinic,” Popular Mechanics Vol. 150, No. 6 (December 1978): 55; Dennis Siamanitis, “Ford’s New Escort: Some Technical Tidbits,” Road & Track Vol. 31, No. 11 (July 1980): 77–80; Russell Earl Silberschlag, assignor to Borg-Warner Corporation, U.S. Patent No. 4,117,918, “Wedging Centrifugal Clutch with Torque Limiter,” filed 28 December 1976, issued 3 October 1978; and U.S. Patent No. 4,305,493, “Friction Shoe Assembly for a Speed Responsive Centrifugal Clutch Assembly,” filed 26 December 1979, issued 15 December 1981; Jim Smart, “How to Build the Perfect AOD – AODetail,” Mustangs and Fords July 2014, www.mustangandfords. com; Vincent M. Staub, Jr., assignor to General Motors Corporation, U.S. Patent No. 4,317,510, “Torque Converter Having a Viscous Drive Portion,” filed 24 July 1980, issued 2 March 1982; Edwin Storm’s Free Car Brochures website at the Old Car Manual Project (storm.oldcarmanualproject.com); Studebaker Corporation, Studebaker Automatic Drive Shop Manual (South Bend, IN: Studebaker Corporation, ca. 1952), and “The New Studebaker for 1951” [brochure D130-11-50], November 1950; Hans Tore Tangerud’s Autoblog website (www.lov2xlr8.no); William K. Toboldt and Larry Johnson, Goodheart-Willcox Automotive Encyclopedia (South Holland, IL: The Goodheart-Willcox Company, Inc., 1975); “Transmissions,” Popular Mechanics Vol. 115, No. 1 (January 1961): 157–158; United Motors Service Division, The Hydra-Matic Transmission 1946-1955: On-the-Car Adjustment Service Manual (Detroit, MI: United Motors Service Division of General Motors Corporation, 1956), and Hydra-Matic Controlled Coupling Transmission Service Manual (Bulletin A-3755) (Detroit, MI: United Motors Service Division of General Motors Corporation, 1 November 1957); U.S. War Department, Ordnance Maintenance: Hydra-Matic Transmission and Propeller Shafts for Light Tanks M5, M5A1, and 75-MM Howitzer Carriage (War Department Technical Manual TM 9-1727C (Washington, DC: U.S. Government Printing Office, 5 February 1943); Matthias Wandel, “Planetary gear ratio calculations,” Woodgears, woodgears.ca/ gear/ planetary.html, accessed 11 August 2016; Bill Williams, “1948 Packard Station Sedan,” Special Interest Autos #17 (June-July 1973), reprinted in The Hemmings Motor News Book of Packards: driveReports from Special Interest Autos magazine, eds. Terry Ehrich and Richard Lentinello (Bennington, VT: Hemmings Motor New, 2001): 51–56; Gary Witzenburg, “The ’82 Fords,” Popular Mechanics Vol. 156, No. 3 (September 1981): 89–91, 168; and Walter A. Woron, “Motor Trials: Packard 200 Is the One to Beat for Comfort and Performance,” Motor Trend Vol. 3, No. 11 (November 1951), reprinted in Packard Gold Portfolio 1946–1958 36–37, 43.
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12 CommentsAdd a Comment
Well Aaron . . another masterpiece. This and the GM automatic history are probably the most definitive descriptions of these technologies on the Internet, excepting pure design and engineering treatises. Well done and thank you; this must have been an enormous amount of work.
I have yet to read this monumental work in depth. Whether it will add to my working knowledge is debatable, but my brain will benefit from the workout.
Aaron is probably now the best informed person in the world regarding the history of automatic transmission development
I appreciate the compliment, but I’m really not! This is a remarkably broad, convoluted, and idiosyncratic field and there’s a LOT I don’t know. For people who want a broader overview, I would recommend a book by Philip G. Gott entitled Changing Gears: The Development of the Automotive Transmission, published by the SAE as part of their Historical Series in 1991. (At this point, an updated, expanded edition wouldn’t go amiss, given all the subsequent development in CVTs and automatics with five or more speeds.)
Smashing read, great job!
I can’t imagine the hours of work which you must have put into understanding these various transmissions, to say nothing of writing up a description that a simpleton like me could (mostly) understand. Another fascinating article, thank you for all your effort!
One thing I’ve always wondered about was if any manufacturers looked into Wilson pre-selector gearboxes as a basis of an automatic. Wilson pre-selectors were pretty well established technology, although not common, by the late ‘30s. Obviously some sort of mechanism would have been required to determine what gear to select and when to actually shift, but starting with a Wilson ‘box at least some of the problems would have been solved. But I’ve never heard of anyone going that route.
The GM team that designed Hydra-Matic was certainly familiar with the Wilson preselector. In fact, Cadillac’s chief engineer ordered an early Daimler Double Six with the Wilson and Laurence Pomeroy’s Fluid Flywheel for evaluation purposes. However, Wilson gearboxes were quite bulky and complex because the nature of their operation required a separate set of epicyclic gears for each ratio, including reverse. With automated hydraulic operation and combinations of brakes and clutches, it was possible to get the same results more efficiently.
Interesting—thanks for the information!
I haven’t studied the Wilson preselectors in any great detail, but if you’re curious, the applicable U.S. patents are US1404675 and US1796904. As you’ll see if you look at the first one, the original iteration had three speeds forward and one reverse, for which it requires four epicyclic gearsets. A Simpson gearset (which I’ll be discussing in great detail in the next few days) provides the same number of ratios from only two gearsets, and a single Ravigneaux gearset can give you four forward speeds and reverse if you have enough clutches. So, you can see how those would be preferred from a standpoint of cost and packaging!
For comparison, a four-speed Wilson pre-selector has four planetary gearsets, four sets of brake bands, and a cone clutch, which is a lot of pieces.
sir im having an issue with my 93 f150 aod. its the mechanically controlled aod. works great no real problems. but the question is when i put my buddys obd code finder on it. the only readings i got was for all the electronically controlled aod. there were around 6 defaults that popped up. i called a trans shop and he had no answer,but it sounded strage to him. if someone would have put in a used ecu ,fron a electric controlled aod. would it work,yet throw out aod default codes. i take it your a writer and not a trans guy ,but maybe someone could answer the question.
I’m not able to provide repair or maintenance advice, sorry!
Thanks for this. New to the site and found it because of this read. As the new owner of a 92 Alante with the viscous clutch I wondered what the difference was. It does drove different than a lock up. It’s weird it’s not noticable as even a new soft engaging lock up but it acts somewhat like it has one. I feel better and it makes more sense now.