The Great Eight: The ZF EIGHT-speed transmission

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Date:6 October 2013 Tags:, , ,

The capable ZF EIGHT-speed transmission is everywhere.

By James Tate

The R4 million Rolls-Royce Phantom and the R250 000 (in the US) Ram 1500 don’t appear to have much in common. One is the acme of automotive extravagance; the other epitomises 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 supplier ZF Group. And these two are not alone. You can find the 8HP paired to many other different engine families.

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. This keeps costs low and maximises potential applications.”

The kit approach even extends to licensing the transmission design to Chrysler, allowing that manufacturer 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 manufacturers 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 300 N.m to a massive 1 000 N.m, but most applications land between 450 and 745 N.m. Further available add-ons include a power takeoff for all-wheel drive, an engine stop/start system, or even a 35-kW 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.