The $400,000 Rolls-Royce Phantom and $24,000 Ram 1500 don't appear to have much in common. One is the acme of automotive extravagance; the other epitomizes blue-collar, working-class values. But as the cliché goes, appearances can be deceiving. Underneath the disparate bodies lies a shared automatic transmission—the ZF 8HP eight-speed, from German-based auto-parts supplier ZF Group. And these two are not alone. You can find the 8HP paired to 25 different engine families in vehicles sold in the United States. If you count every make, model, body style, and driveline configuration, the number of places where this transmission shows up is enormous.
The popularity of the 8HP isn't all that surprising given current industry trends. Adding more speeds to a transmission helps efficiency: Extra gears allow for a wider spread of ratios and let the engine keep the revs low whenever possible, saving fuel. What makes the 8HP novel, however, is its staggering versatility.
Being All Things To All People
According to ZF's Bryan Johnson, the 8HP is popular because it is a great multitasker. "We design it to be as flexible as possible," Johnson says. "We sell it as a kit, rather than working to fit within the unique constraints of one manufacturer—which keeps costs low and maximizes potential applications." The kit approach even extends to licensing the transmission design to Chrysler, allowing the automaker to ensure a steady supply for its own vehicles and freeing ZF from the risk of production shortages.
According to Johnson, the 8HP has fewer parts than the company's previous 6HP six-speed automatic and still fits in the same packaging. That means manufacturers need to make only minimal changes to adapt the 8HP to existing powertrains and need not worry about major structural issues. ZF works most closely with automakers on the software side, adjusting the transmission's electronic calibration for things such as shift strategy and the speed of the gearshifts.
But the options on the 8HP go beyond software programming. Different internal clutch packs can be used depending on a manufacturer's specific torque requirements. The transmission has a range of 221 lb-ft to a massive 738 lb-ft, but most applications land between 330 and 550 lb-ft. Further available add-ons include a power takeoff for all-wheel drive, an engine stop/start system, or even a 47-hp electric motor in place of the torque converter for hybrid vehicles.
So far, the 8HP has been a hit. Automotive News awarded ZF its PACE award in 2010 for the 8HP, and the transmission continues to make its way into new models. Our experience in cars outfitted with the 8HP is that you hardly notice when it's working, which is exactly how an automatic transmission should operate. Any criticisms of the 8HP have to do with the individual tunings a carmaker applies rather than with the unit itself.
If there is one cause for concern with the 8HP, it's the transmission's sheer pervasiveness. The biggest risk when a single manufacturer supplies so many companies is widespread production delays or recalls if any problems arise. Fortunately, the 8HP has a trouble-free record. As for any doubt that the same transmission can service two—or even dozens of—completely different vehicles, ZF is proving that argument to be as silly as confusing a Rolls with a Ram.
James Tate has been writing about cars professionally since 2004, but the obsession took hold before he could stand. He's a Luddite at heart, so it's the tactility and driving experience of yesterday's cars that really grab him, but an appreciation for engineering sustains his interest in the modern stuff. Tate’s writing has appeared in Road & Track, Popular Mechanics, Automobile, Autoweek, and others.
