AUTOMATIC TRANSMISSION GETS ROLLING
When talking about the origins of GM’s early automatic transmissions, it’s important to understand that for the first seven decades of its history, the corporation was not nearly as monolithic as the modern enthusiast or historian might assume. Each division operated more or less independently and was largely autonomous, responsible for its own engineering, manufacturing, and sales. There were occasional collaborative projects, but in general, if the divisions needed something engineered or manufactured by another GM division, they had to buy it like any other customer.
While each division did much of its own R&D work in those days, GM also had central Research Laboratories, headed from 1920 to 1947 by the inimitable Charles F. Kettering, famously the inventor of the automotive self-starter. The research engineers operated independently of the production divisions, conducting advanced engineering and research projects to develop technology (not necessarily automobile-related) that could be adopted by different GM divisions and/or licensed to outside companies. The Research Laboratories worked on all manner of projects, ranging from high-compression engines and leaded gasoline to hydraulic valve lifters.
In the twenties, the work of the Research Laboratories was primarily on the theoretical and experimental side. If a particular invention seemed worthwhile, one or more divisions would be drafted (not always happily) to work with the research engineers to develop the idea for production. In 1931, the corporation organized a central Engineering Staff, led by VP of engineering Ormond E. Hunt, that could serve as a bridge between the research engineers and the divisions. However, ultimate responsibility for the production version of any specific concept or invention still (usually) rested with the individual division, which sometimes led to different divisions offering several distinct variations on the same basic technological theme.
As you would expect, the Research Laboratories worked throughout the twenties to find alternatives to the dual-shaft transmission, exploring a wide variety of electromagnetic, hydraulic, and friction drive systems. These efforts took on some additional urgency after Alfred P. Sloan became president of General Motors in 1923. While he was no fan of engineering novelty for its own sake and had strongly opposed some of Kettering’s wilder ideas — such as the ill-fated “Copper Cooled” Chevrolet — Sloan was by his own admission a mediocre driver who could not use a conventional gearbox with any skill. Recognizing that there were many like him, Sloan understood that a reliable and effective self-shifting transmission would have powerful commercial potential.
Cadillac became involved in this work in the late twenties or early thirties when the division was assigned to support Buick in the development of an ambitious infinitely variable friction drive transmission that the Research Laboratories’ Dynamics unit had conceived. (It appears the friction drive unit was based on one or more outside patents that GM had either purchased or licensed, although the scant information we’ve found on the design’s origins is confusing and contradictory.) Nicknamed the “Roller,” the transmission used two sets of toroidal races, one set driven by the engine, the other set connected to the output shaft; power was transmitted between the races by a series of adjustable rollers.
The Roller’s development was protracted and difficult. The friction drive transmission was extremely smooth and potentially very efficient, but its mechanical complexity made it frighteningly expensive and its reliability remained at best suspect. Cadillac eventually withdrew from the development in favor of an entirely different project, conceived in-house by Thompson. It was just as well; Buick would never offer a production version of the Roller.
Thompson’s ideas on automatic transmission focused not on friction drive, but on planetary gearsets. Cadillac had actually used epicyclic transmissions many years earlier, although that had been well before Thompson’s time; Cadillac switched to dual-shaft transmissions back in 1908. Thompson’s direct inspiration was the 1931 Daimler Double Six, a copy of which Seaholm had purchased for evaluation in late 1930 or early 1931. The Daimler was fitted with the four-speed Wilson preselector transmission and a novel new feature: the Fluid Flywheel, the first fluid coupling ever offered in a production passenger car. (See the sidebar below.)
Even with the Fluid Flywheel, the Wilson gearbox still required manual gear selection, but Thompson recognized that the combination contained most of the ingredients for a practical fully automatic transmission.
THE MILITARY TRANSMISSION PROJECT
In early 1932, Seaholm assigned engineers Ralph F. Beck and Walter B. Herndon to assist Thompson with his automatic transmission project, which was dubbed the “Military Transmission.” Although the project would eventually have military applications, the moniker was just a codename, intended — like the ominous “Keep Out” sign hung outside the door — to discourage prying eyes.
The Military Transmission project’s objective was to develop a planetary gearset that could be operated automatically by means of hydraulic servos. The first fruit of this work, on which Thompson filed a patent in March 1933 (subsequently U.S. Patent No. 2,285,760), was a conventional sliding-gear transmission augmented by a two-speed planetary gearset that provided automatic shifting between direct drive and overdrive ratios. The design was similar in broad principle to the new Reo Self-Shifter, patented two years earlier and announced in May 1933 as a production option for the 1934 Reo Royale and S-4 Flying Cloud. For Thompson, the semiautomatic transmission appears to have been mostly an early essay in speed-sensitive hydraulic governor systems, suggesting the direction of his thinking.
Around the time Thompson’s patent was filed, Seaholm expanded Thompson’s group from three engineers to five, adding William L. Carnegie and Maurice S. Rosenberger to the team. They soon began work on a more elaborate hydraulically operated planetary transmission, which had reached the prototype stage by mid-1934. Thompson applied for a patent on it that October.
Unfortunately, the entire project was rapidly becoming an unaffordable expense. For several years, Cadillac general manager Larry Fisher had been spending lavishly on new products and new technology, including double wishbone suspension, power steering (which for various reasons Cadillac wouldn’t actually offer until 1952), and of course the V-16 and V-12 engines. The results were often impressive, but with Cadillac sales slumping badly as the Depression worsened, the division’s future was very much in question. Service manager Nicholas Dreystadt, who succeeded Fisher as general manager in June 1934, convinced the corporation to give Cadillac a reprieve, but severe budget cuts left the Military Transmission project hanging by a thread.
By this time, Buick’s friction drive transmission had been canceled, so for Thompson’s work to go the same way would have been a significant setback to an effort that still had Sloan’s strong personal interest. The eventual answer was to transfer Thompson’s project to O.E. Hunt’s corporate Engineering Staff, which had its own facilities and budget. In January 1935, Thompson and his team moved to the central offices to become a corporate product study group, later named the Transmission Development Group.
THE AUTOMATIC SAFETY TRANSMISSION
By this time, Thompson had developed a new four-speed semiautomatic transmissions, patent applications for which were filed in October 1934 and October 1935 (U.S. Patent Nos. 2,195,605 and 2,193,304 respectively). The transmission used two servo-operated planetary gearsets with an additional set of spur gears, interposed between the clutch and front gearset, for neutral and reverse. Thompson specified a conventional single-plate friction clutch, but it was strictly a stopgap. He still wanted to eventually substitute a fluid coupling, but his tiny team hadn’t yet had time to design a suitable one.
The semiautomatic transmission’s rear servo (and thus the rear gearset) was controlled by the driver using a selector lever on the steering column, but the front servo functioned automatically, shifting from direct drive to reduction and back based on throttle position and road speed; the latter was signaled by a centrifugal governor driven by the transmission output shaft.
The idea was that the driver would start in Neutral, disengage the friction clutch with the clutch pedal, and select Low for a first-gear start, followed in short order by an automatic shift to second. Obtaining third and fourth required shifting manually from Low to High (which did not require de-clutching). The transmission would then shift automatically between third and fourth gears.
Some time after Thompson’s group moved to the Engineering Staff, their project came to the attention of Oldsmobile general manager Charles L. McCuen. We don’t know if McCuen was aware of Buick’s now-canceled friction drive project, but he was in any case very keen for Oldsmobile to have an automatic transmission of its own. He ordered Oldsmobile chief engineer Harold T. Youngren to work closely with Thompson’s group to adapt their ideas into something Oldsmobile could build and sell.
Later that year, senior corporate management decided that the manufacturing portion of the equation should be handled by Buick, which had unused factory space that could be retooled for the purpose. Buick was also ordered to share the new transmission, presumably as a sort of consolation prize for the abortive Roller project. That directive sat ill in Flint; Buick engineers still had their own ideas about automatic transmission (some of which would be realized in the postwar Dynaflow) and had no love for the Automatic Safety Transmission, which they hadn’t developed and didn’t want.
Throughout this period, Thompson continued to refine the semiautomatic transmission, applying for an additional patent in March 1937 (U.S. Patent No. 2,362,418). Production began around the same time and the new transmission, which Oldsmobile dubbed the “Automatic Safety Transmission” (AST), went on sale in June as an option for the 1937 Oldsmobile Eight. List price was initially $80, rising to a hefty $100 that fall, when availability was extended to six-cylinder Oldsmobiles and the Buick Series 40 Special. Buick doesn’t appear to have bothered coming up with a specific trade name for the semiautomatic, describing it simply as a self-shifting transmission, but it was otherwise identical to the Oldsmobile unit.
By the time the Automatic Safety Transmission appeared on the market, Reo’s Self-Shifter had come and gone and buyer interest in semiautomatic transmissions had proven to be limited. Not only were the transmissions complicated, expensive, and often troublesome, they were still not really automatic. While their operation was different than that of a conventional transmission, saying they were easier to use (much less safer, as Oldsmobile claimed) was arguable, particularly since they retained the clutch pedal, of which many American motorists would have been happily rid. (This lesson was apparently lost on Chrysler, which by 1937 was working on its own M3 semiautomatic transmission for a 1940 introduction.)
It certainly didn’t help that that the Automatic Safety Transmission wasn’t very reliable, particularly early on. The transmission’s teething problems were extensive and Oldsmobile found that Buick engineers and production people, eager to wash their hands of the project, were not much help. The transmission was also unfamiliar territory for technicians and Oldsmobile did not encourage tinkering, in part because it took a while for even the factory production engineers to figure out how to resolve certain common issues. As a result, dealers responded to most problems by pulling the transmission and replacing it with a new factory-refurbished unit. (Substituting a standard gearbox, which some unhappy owners would probably have preferred, was a more complicated chore that required also replacing the steering column, the entire driveshaft, and ideally the rear axle gears.)
Buick dropped the semiautomatic transmission after only a year and never offered the unit in their bigger cars, but Oldsmobile persisted through the 1939 model year, reducing the list price by $25 for the transmission’s final season. Total production, which continued through September 1939, was limited. We have no exact figures, but we’ve seen estimates ranging from about 15,000 to as many as 40,000. Buick took only about 3,000 of those for itself, so most went into 1937–1939 Oldsmobiles. Warranty costs were high and the Automatic Safety Transmission’s suggested retail price was considerably less than Oldsmobile paid Buick for each transmission, so Oldsmobile undoubtedly lost money on the whole endeavor. However, if nothing else, the project provided plenty of real-world experience for the fully automatic transmission Thompson and McCuen still hoped to offer.