The MGF and MG TF automatic gearbox is a Continuously Variable Transmission (CVT) made by ZF, marketed as Steptronic on early installations and as Stepspeed after BMW retained the Steptronic name following its disposal of Rover in 2000. The two names describe the same physical gearbox, earlier MY2000 MGF automatics carry Steptronic badging, later MGF automatics and all MG TF 120 Stepspeed cars carry Stepspeed badging, but the internal hardware is identical. In fully automatic mode the gearbox operates as a true CVT, belt-and-pulley architecture providing an infinitely variable ratio within its operating range. In 'manual' mode, the ECU imposes six pre-set ratios onto the CVT hardware, producing a simulated stepped-ratio feel that the driver selects via push buttons on the steering wheel or the floor-mounted gear lever.
The six ratios were ahead of their time in concept, predating the paddle-shift automatics that became common on performance cars a decade later, and provided a 'manual' driving experience with the CVT's underlying smoothness intact.
Application and Variant
The CVT was exclusively paired with the 1.8-litre K-series engine in 120 PS non-VVC tune. It was never offered on the VVC, 1.6-litre, MG TF 135, or MG TF 160 models, the higher-output variants were manual-only. On the MG TF, the CVT-equipped model was designated MG TF 120 Stepspeed. Production continued through the NAC/SAIC revival era (2008 to 2011), with a SAIC-era variant of the gearchange mechanism that differs from the pre-2005 part, both variants are catalogued.
Driving Characteristics
The Stepspeed has distinctive operating characteristics that owners should understand. In 'D' (Drive) mode, the ECU caps the engine at approximately 4,500 rpm, prioritising economy and comfort. In Sport mode, the rpm cap rises to approximately 5,500 rpm, providing livelier response. In Manual mode (using the push-buttons or floor-change), the rpm can be held up to approximately 6,000 rpm, matching the engine's useful power band.
Published performance figures for the MG TF 120 Stepspeed are: 0 to 60 mph in approximately 9.4 seconds, top speed 118 mph, combined fuel consumption 34.9 mpg (8.1 l/100km), CO2 emissions 194 g/km. These figures are slightly behind the equivalent manual cars, the CVT's internal hydraulic pumping losses account for the efficiency gap rather than any engine-coupling inefficiency.
Drive Plate, The CVT's Flex Plate
The drive plate is the CVT's equivalent of the manual gearbox's flywheel, a thin flexible steel disc bolted to the crankshaft that transmits torque into the CVT's input coupling. Unlike a flywheel, the drive plate has no significant rotational mass of its own; the Stepspeed does not need the inertia that a manual flywheel provides because there is no manual clutch to drive. The drive plate is cross-compatible with the MG ZR automatic applications using the same CVT. A damaged drive plate, typically cracked at the crankshaft bolt circle from repeated heat cycling, produces a distinctive vibration at idle that worsens with engine speed and is distinct from engine imbalance issues.
Drive plate replacement requires separating the engine and gearbox, which on the mid-engine MGF and MG TF means dropping the rear subframe, the labour cost makes this a job usually combined with other major service work.
Gearchange Mechanism, Original and SAIC-Era Variants
Two gearchange mechanism assemblies are catalogued. The original type fits MGF from MY2000 through MG TF production up to the 2005 MG Rover collapse. The SAIC type fits the NAC/SAIC-era MG TF automatic variants produced from 2008 onwards at Longbridge from Chinese CKD kits. The two mechanisms have different internal ratchet and detent arrangements and are not interchangeable, confirm car era (pre-2005 or NAC/SAIC) before ordering.
The mechanism incorporates the gear selector lever, the shift-lock solenoid (preventing shift out of Park without ignition on and brake pedal pressed), and the electrical switching for the ECU's gear-position sensing.
Selector Cable and Link Rod
The external actuation between the gear lever and the CVT uses a combination of a selector cable (with its dedicated support bracket) and a selector shaft link rod at the CVT end. Both items are catalogued individually for replacement, worn selector cable or link rod produces vague gear engagement feel, difficulty finding Park reliably, or warning lights indicating the ECU cannot confirm the lever position. The support bracket for the selector cable is a CVT-specific item and is not shared with the manual gearbox installation.