ZF Gearboxes Explained: 6HP, 8HP, 9HP and Dual-Clutch Units

What "ZF gearbox" means and how to read the codes

"ZF gearbox" means any transmission designed and built by ZF, and its type code gives the number of gears, the layout and the size class:

• The first digit is the number of forward gears (6, 8 or 9).
• HP stands for a hydraulic converter combined with planetary gearsets; DT marks a dual-clutch transmission, as in the 8DT.
• The number that follows is the size class. In the 8HP family it is the nominal torque, so an 8HP 70 handles about 700 N·m (516 lb-ft). In the first 6HP generation it gave the input shaft diameter: the 6HP26 has a 26 mm (1.02 in) shaft.

The exact variant is on the type plate on the casing or can be confirmed from the VIN. For terms such as torque converter or mechatronic unit, see our car terms dictionary.

Who makes ZF gearboxes

ZF Friedrichshafen AG makes them. The company was founded on 20 August 1915 in Friedrichshafen by Ferdinand von Zeppelin and Alfred von Soden-Fraunhofen to supply gears for Zeppelin airships. The Zeppelin Foundation owns 93.8% and the Dr. Jürgen und Irmgard Ulderup Foundation 6.2%. Published figures put 2025 revenue at EUR 38.8 billion with about 153,000 employees, and TRW Automotive joined the group in the mid-2010s.

ZF entered the car market in 1919, and series production of the 3HP20, its first passenger-car automatic, began in 1969. The four-speed 4HP22 followed in 1980 and stayed in production until 2003. ZF also builds truck and bus gearboxes, outside the scope of this guide.

Why so many brands use ZF

Many carmakers buy a proven automatic and write their own software for it. One 8HP family covers four-cylinder engines and large V12s through its torque classes. Each carmaker still sets its own shift calibration, cooling and service schedule, so the same gearbox can behave differently by brand.

How a ZF torque-converter automatic works

A ZF automatic drives through a fluid coupling and selects ratios by locking parts of planetary gearsets with hydraulic clutches.

• Torque converter: transmits drive through fluid, multiplies torque when pulling away and has a lock-up clutch that joins engine and gearbox mechanically to cut slip.
• Planetary gearsets: sun, planet and ring gears provide every ratio without sliding gears in and out of mesh.
• Clutches and brakes: wet multi-plate packs hold or release gearset elements; a shift is one releasing while another engages.
• Mechatronic unit: the valve body and control electronics sit together inside the gearbox and decide when and how firmly to shift.

The 6HP uses a Lepelletier arrangement, a simple planetary set combined with a Ravigneaux set. Ford's 6R and GM's 6L are separate designs built on the same type of gearset.

The ZF family at a glance

The table covers the ZF car gearboxes owners ask about most.

The ZF 8HP in detail

The 8HP is ZF's eight-speed automatic for longitudinal engines, designed at ZF Saarbrücken and launched in 2008-09 in the BMW 760Li; sources differ between a 2008 introduction and a 2007 premiere with production from 2009. Toyota's AA80E reached production first, in 2007, but the 8HP became the most widely used eight-speed.

First gear is about 4.7 to 5.5 and eighth about 0.64, a ratio span of 7.04 on early units and up to 8.59 on later ones such as the 8HP 76. ZF quotes shift times down to 0.2 seconds and a fuel saving over the 6HP given as 11% in one source and 12% in another. A third generation arrived in 2018.

The one millionth 8HP was reported in August 2011. Users include BMW, Audi, Jaguar, Land Rover, Alfa Romeo, Maserati, Bentley and Rolls-Royce, while Stellantis builds the gearbox as the TorqueFlite 8 for Chrysler, Dodge, Jeep and Ram at Kokomo and Gray Court, South Carolina. Hybrid versions put an electric motor inside the housing: 48 V mild hybrids and plug-in versions of up to 160 kW (215 hp). The torque class is matched to the engine, whose figures you can check in our engine database.

6HP, 9HP and ZF dual-clutch gearboxes

Each of these answers the goal of more gears in less space in its own way.

6HP: the six-speed generation

The 6HP26 is usually cited as the first six-speed automatic in a series-production car, the BMW 7 Series (E65), from around 2001, with a second generation (6HP21 and 6HP28) in 2007. Owners and critics link a converter that locks up in all gears, and the sealed pan with "lifetime" fluid, to later problems. No neutral dataset confirms it.

9HP: nine gears for transverse engines

Land Rover and Jeep showed the 9HP at the 2013 Geneva motor show, and the 2014 Jeep Cherokee (KL) was the first car sold with it. Two dog clutches made it 6 mm (0.24 in) longer but 7.5 kg (16.5 lb) lighter than the six-speed it replaced. Early Jeep, Chrysler and Acura owners reported slow or noisy shifts; ZF attributed them to software, Chrysler issued a service bulletin for the 2014 Cherokee, and Acura recalled the 2015 TLX over its transmission.

8DT and 7DT: the dual-clutch units

ZF builds the seven-speed dual-clutch gearbox Porsche sells as PDK. Its successor, the 8DT, announced in February 2017, handles up to 1,000 N·m (738 lb-ft) in three torque classes with wet multi-disc clutches. Its hybrid module, developed with Porsche, delivers 100 kW (136 PS) and allows electric driving up to 140 km/h (87 mph). Volume production began for the Porsche Panamera at ZF's Brandenburg plant.

Servicing a ZF automatic: what owners should know

The vehicle manufacturer's schedule and fluid specification apply, not a generic ZF rule. Many carmakers call the fluid a "lifetime fill", meaning their schedule lists no change; it does not prove the fluid lasts as long as the car. No ZF-published interval could be confirmed for this guide, so ask a dealer or an independent transmission specialist what suits your mileage, towing and climate.

Use only the fluid grade named in the handbook. A level check usually needs the engine running and the fluid within a set temperature range, so it is a workshop job. Signs of trouble include:

• harsh or delayed engagement of D or R;
• flare, where engine speed rises between gears;
• a bang or shudder on shifts;
• a gearbox warning on the on-board computer or a limp-home mode.

In cold weather the fluid is thick, so drive gently at first. A liquid engine pre-heater warms the engine, but the gearbox reaches working temperature only as you drive. On snow, a winter mode, where fitted, works best with suitable winter tyres.

Buying a used car with a ZF automatic

Judge the gearbox on its history and behaviour, not on the supplier's name.

1. Identify the gearbox code from the VIN or type plate.
2. Check the service history for fluid changes, with dates, mileage and the fluid used.
3. From cold, select D and R several times; engagement should be prompt without a thump.
4. Repeat when fully warm, as some faults appear only with hot fluid.
5. Accelerate gently and then firmly through all gears, including kickdown, feeling for flare, slip or hard shifts.
6. Have the gearbox control unit's fault memory read, not only the engine's.
7. Ask whether software updates have been applied, especially on early 9HP cars.
8. Check open recalls for the VIN and any remaining warranty.

Common mistakes to avoid

Most costly problems start with neglect or assumptions, not the design.

• Treating "lifetime fill" as a promise on a high-mileage car.
• Using a fluid that is not on the carmaker's approval list.
• Blaming ZF for shift quality set by the carmaker's calibration.
• Towing or tuning beyond the torque class the gearbox was specified for.
• Resetting adaptation values without a reason.

For more drivetrain terms, the 1cars glossary is a quick reference.