TECH: TOPICS
Fans of Porsche's frontengined, water-cooled sports cars will likely have heard of the ‘torque tube’ driveline integral to their construction, evident ever since introduction of the 924. Not everybody understands what a torque tube is, though. There is, in fact, much more to it than a steel cylinder surrounding the driveshaft. What's more, the idea made it onto all-wheel-drive versions of the 911.
While Porsche can't lay claim to inventing the torque tube, it certainly did a good job of taking ownership of the idea. In this article, we take a look at the design and functionality of the torque tube and, just as importantly, the other components making it work. And, with the help of Georgia-based Porsche driveline specialist, Black Sea Research & Development, we'll highlight the weaknesses in the torque tube setups of various Porsche legacy models.
Our hope is to help you make your torque tube-equipped Porsche drive better than ever.
In many front-engined, rear-drive vehicles – old or new – the gearbox is attached directly to a longitudinally mounted engine. A driveshaft bolts to the output shaft of the gearbox, bringing drive to the rear-axle differential. This is part of what's known as the Hotchkiss drive. In manual cars, there's a clutch between the engine and the input shaft of the gearbox to interrupt drive, facilitating the changing of gears. When Porsche and Audi were working to develop a new line of sports cars in thea four-speed manual transaxle based on an Audi unit was initially chosen. Positioning the gearbox at the rear of a front-engined car significantly enhances weight distribution, as evidenced by the 924's 48:52 front-to-rear weight ratio. It's then a case of working out how to bring drive from the engine to the gearbox.
