A Quick Guide to the ZF 8-Speed Transmission

What do the transmissions of famous European cars like the BMW 7 Series, Jaguar XF, and Rolls-Royce Ghost have in common? They all use a variant of the ZF 8-speed transmission, which also appears in American vehicles like the Dodge Durango, Jeep Grand Cherokee (WK2), and RAM 1500 (DT). Let’s take a closer look at the ZF 8-speed transmission and find out why experts call it one of the best transmissions today.

What is the ZF 8-Speed Transmission?

Officially called the 8HP automatic transmission, the ZF 8-speed transmission is designed to work with longitudinal engines in rear-wheel drive (RWD) and 4-wheel drive (4WD) cars. Longitudinal engines have a crankshaft that’s positioned parallel to the long axis running from the car’s front to the rear.

8HP is an acronym. First, the number 8 stands for the number of forward gears in the gearbox, allowing the car to operate within 8 different speed ranges. Next, the capital letter H indicates it uses a hydraulic converter to transfer and convert engine power into torque that drives the wheels. Finally, the capital letter P represents the use of planetary gears.

The ZF 8-speed transmission was designed by German company ZF Friedrichshafen AG, a technology manufacturing company. First produced at the ZF factory in southwestern Germany, the 8HP design was licensed to car maker Stellantis, which owns brands like Chrysler, Dodge, and Fiat.

Millions of ZF 8-speed transmissions have been built by both ZG and Stellantis for various manufacturers. Aston Martin, BMW, Jaguar, Land Rover, and Volkswagen are just some of the European car manufacturers that use the 8HP transmission in various vehicles.

What Can the ZF 8HP Transmission Do?

The ZF 8-speed transmission shifts between gears so smoothly and quickly that even fans of manual cars might enjoy trying out this automatic system. The gearbox contains 4 planetary gear sets, 3 clutches, and 2 brakes. The 8HP parses these parts into 8 forward ratios, enabling its namesake 8 speeds.

Its one-gear and two-gear shifts use only a pair of gear-shifting elements. One element opens while another one shuts. The ZF 8-speed transmission can also pull off specific multi-gear shifts, such as going from 6th gear to 3rd gear or 8th gear to 2nd gear.

Modularity

Aside from its excellent shifting, the ZF 8-speed transmission is a modular design with many variants for different torque output requirements. Depending on the variant, the ZF 8HP automatic transmission can produce as low as 162 pound-feet and as high as 770 pound-feet of maximum torque.

Compatibility

Thanks to its modularity, the ZF 8HP transmission can work with different all-wheel-drive and four-wheel-drive systems, including those that use an integrated center differential or a two-speed transfer case.

It’s also compatible with hybrid and plug-in hybrid vehicles. Instead of a torque converter, the ZF 8-speed transmission features an electric motor to drive the wheels. The BMW 7 Series Hybrid is a good example of a hybrid with an 8HP transmission.

Parts Commonality

ZF 8-speed transmissions across various makes, models, and types share many core elements. It’s easier and more affordable to come up with a new variant for a different vehicle. While you can’t simply transplant the 8HP gearbox in the BMW 7 Series into a Dodge Durango, the two variants can probably swap certain parts.

What Sets the ZF 8-Speed Transmission Apart From Other Transmissions?

Improved Efficiency

The ZF 8-speed transmission achieves higher efficiency than the earlier 6HP transmission by reducing the parts it needs to operate efficiently.

Its four gear sets only require 5 shift elements, and each gear only opens two of the elements. An open element generates drag that reduces the torque transferred to the wheels. This minimizes the number of elements, reduces total drag, and preserves torque.

In addition to needing and using fewer shift elements, the ZF 8-speed transmission also cuts down the necessary number of clutches and brakes to only 3 multi-disc clutches and 2 brakes. It achieves the reduction thanks to a parallel-axis vane cell oil pump that helps provide extended start-stop and coasting functions.

Lightweight But Powerful

Depending on the variant, the ZF 8-speed transmission can produce 220 to 1,000 Newton-meters (N·m) of torque. This torque range makes it suitable for a wide variety of vehicles, including smaller mid-size cars, luxury vehicles, and SUVs.

Furthermore, the 8HP transmission manages to cram an additional 2 gears into the same dimensions as the earlier 6HP design. And the 8HP also shaves off precious pounds of weight to help improve performance.

To give you a better idea, let’s look at the 8HP70 transmission used in a car like the Audi RS6. The 8HP70 is a mid-size model that only weighs 174 lbs (87 kg) when fully topped with oil. It’s 3% lighter than the preceding 6HP transmission. It also keeps the engine running at the optimum point, reducing fuel consumption during acceleration.

Enhanced Fuel Efficiency

The ZF 8-speed transmission is so efficient that it reduces average fuel consumption and CO2 emissions in cars by 3%. In hybrids, the 8HP transmission combines this with the benefits of the electric drive for even more savings.

Optimized Performance

ZF refined its 8-speed transmission in several ways to enhance its performance. From reduced drag torques to lower system pressures to torsional dampers that transmit power and reduce speed more efficiently, the 8HP transmission can handle future engines with different cylinders.