This spring towards the end of a series of articles on Citroën and Adolphe Kegresse, I mentioned his invention of the dual clutch transmission and its widespread use by the VW group and Porsche. Despite my cracking jokes about the farting exhaust noises they make when shifting, DCT or PDK (as Porsche call their version) is no laughing matter. Apart from the fuel efficiency advantages offered by the elimination of a torque converter, thereby avoiding the energy loss inherent in the age-old setup, direct clutch gearboxes offer unsurpassed speedy shifts which can make the difference between winning and losing in racing.
The innards of a modern PDK transmission from a Porsche 918
While Adolphe Kegresse was in the employ of Citroën when he invented the DCT and a Traction Avant was used as a test mule, André Citroën believed there to be only a very small market for the technology. Commercializing the DCT would be exorbitantly expensive and Citoën did not sell luxury model capable of amortizing the cost. One would have to sell the concept to Delahaye or Delage or even a British company like Daimler or Rolls Royce. But this was the age of the preselector gearbox for which the luxury car market had fallen hard – even Cord in the USA had them. So the concept was shelved and there it remained until the 1980’s.
By the 1980’s the patents had run out and so various companies began to tinker. Ironically, it was Harry Webster of Automotive Products in Leamington Spa who installed a DCT into a Ford Fiesta Mk1, Ford Ranger, and Peugeot 205 for testing. The company had started out building American Borg & Beck clutch systems for cars in England and the colonies and become famous for designing the first fully automatic transmission for a front drive car which was offered as an option in the Austin Mini. Automotive Products patented their DCT design in 1981 but neither Ford not Peugeot would put it into production.  All these early twin-clutch prototypes featured a single dry clutch combined with a multiplate wet clutch and this was what was patented, but…
Secretly in the outskirts of the little town of Weissach in the district of Böblingen in the Federal Sate of Baden - Württemberg in the then still very much West- Germany, Porsche engineers had been tinkering with the concept of a DCT since the 1960’s. To fill the gap in the meantime while vehemently refusing to install a conventional automatic in one of their legendary sportscars, they had commercialized an automated manual transmission called Sportomatic which used a solenoid activated by the shift lever to engage and disengage the clutch. When the gear lever was touched the clutch would disengaged and it was reengaged when the drivers hand left the lever. A torque converted replaced the flywheel which allowed the car to remain stationary with the clutch engaged but also sapped some power. All in all, Sportomatic was relatively inexpensive, popular but imperfect and during its long production - run Porsche’s secret tinkering had paid off. By the early 80’s they had come up with a DCT that worked…. until it didn’t and puked its guts onto the tarmac. 
Sport - O - Matic: Not quite Sport and Not Quite Matic.
Despite its unreliability and quite possibly amidst a bout of German humor, Porsche tested the new concoction on their unsuspecting Group C Sports Car Drivers. At the 1986 1000 kms of Fuji it was Derek Bell’s turn to be used as Guinee pig. His car sported two new unproven technologies: PDK and ABS. Bell felt penalized by the extra weight and according to his account years later at the launch of PDK in the 997 series of Porsche 911 in 2008, he threw a “wobbly”(British slang for a hissy fit.). He had done this once before at Porsche’s introduction of electronic fuel injection which proved a bit buggy at first, but this time he was livid. Porsche had been running experimental versions of PDK on the 962 since a test at Paul Ricard in 1986 but it soon became clear that the system was not yet up to running a full 1000 km endurance race but Bell and Hans Stuck were content to run it for shorter races. At Monza they had actually won with PDK but by the time Fuji came around at the end of 1986, and Porsche were now adding ABS to the mix, Bell lost it. With the heavy PDK box alone behind the engine the car felt like it was pulling a trailer and with the ABS control unit added to the now rather more porky 962 it would surely cost him the 1986 championship. After complaining to Peter Falk, (not of Colombo fame but Porsche’s Director of Racing) Bell’s moaning reached Board level and Peter Bott (board member responsible for research and development) told Bell he could choose between either PDK or ABS but it had to be one. Bell grudgingly chose PDK for the Fuji race but kept eying the trailer that held the manual gearboxes mumbling that if only he had one in his car his World Championship hopes would remain intact. Nevertheless, Derek Bell - ever the good sport, was willing to take one for the team.
Derek Bell and Hans Joachim Stuck's Porsche 962 C N0. 002 at Mt. Fuji.
As it does at Mount Fuji, it poured on the day of the race. ABS might have been more helpful. Furthermore, as it was wont to do, the PDK unit broke a half - shaft but Porsche had become so adept at swapping half - shafts in the blink of an eye that Derek Bell and his co-driver Hans Joachim Stuck still managed to finished the race in 25th place and Bell became World Champion of the second year in a row. 
Between the 1980’s and 2008 when PDK was finally introduced on Porsche road cars and its cousin DSG on Audi’s and VW’s, Weissach took their time improving the reliability of the system. In the meantime, while swallowing their pride, Porsche finally caved and sank to the ignominy of installing a torque converter automatic in their 1989 964 series of the 911. While in basic design a conventional auto box, it sported smart computer algorithms that adjusted the shift points to ones’s driving style while a manual mode called Tiptronic kept the more sporting Porschephiles happy. The majority of Porsches customers still preferred to shift their own gears, but Tiptronic launched a heard of copycat systems throughout the industry. Even Daimler Benz joined the party, co-developing a system with its new partner Chrysler. To this day only the wonks in Auburn Hills fully understand why their shift lever toggled left to right instead of fore and aft like the rest of the civilized world.
Tiptronic: The Smart Slush Box that launched a thousand copycats.
Meanwhile, Ferrari and later BMW had implemented single clutch sequential systems with paddles which were more intuitive to use but jerky in their shift quality. And then in 2008 Porsche and VW launched DCT’s throughout their model lines from the 911 down to the lesser Golf GTI. At long last the fiddly little toggle switches on Porsche steering wheels were gone replaced by electric paddle shaped buttons behind the steering wheel spokes. Less “Schumi” than what Ferrari offered but cheaper to produce and in some cases more intuitive to use.
Today almost everyone from Zuffenhausen to Pyongyang offers a DCT in their lineup. America is still not fully convinced, but that may have something to do with reliability problems currently plaguing the DCT found in various Ford Products. It has recently become the object of a class action lawsuit. Maybe if Ford and their supplier can solve the problem, ‘Murica too can be pried away from the slush boxes of old and dragged kicking and screaming into the 21st century.
Ford's DCT and the "Smoking Clutches of Destruction"