Reconditioned BMW Gearbox on an exchange basis

BMW Gearboxes: 6-Speed Manual Diesel and Petrol – Two Distinct Worlds

For the BMW models covered here — 1 Series, 2 Series Gran Tourer, 3 Series, 4 Series, 5 Series, X1, X3 and X4, from 2003 to 2022 — the range focuses exclusively on the 6-speed manual gearbox, in both diesel and petrol versions. No ZF 8HP automatic, no torque-converter Steptronic: the references listed cover reconditioned manual gearboxes on an exchange basis only. This is the first thing to check before starting your search.

Diesel and Petrol: Similar in Appearance, Different in Practice

Diesel units (M47, N47, B47, M57, B37) and petrol units (M54, N52, N53, N54, N55, B48, N20, N43, N46) both use 6-speed manual gearboxes from the same GS6 family, but their internal variants differ: gear ratios, torque capacity, length and manufacturer references (e.g. GS6-17DG for petrol, GS6-37DZ for diesel) are not interchangeable. Fitting a petrol gearbox to a diesel engine — or vice versa — is a common mistake when relying on engine capacity alone without checking the engine code.

Identification: Engine Code Takes Priority Over Engine Capacity

The 2.0d is a good illustration of the problem: depending on the year and model, you may find a M47D20, N47D20, N47D20A or B47D20 — four distinct engine codes, each potentially requiring a different gearbox. Likewise, the 3.0 petrol covers codes ranging from M54B30 (older generation) to B58B30 (440i, recent generation), with very different architectures and torque figures. On the 3.0d, the manufacturer designations 306D2, 306D3 and 306D5 correspond respectively to engine codes M57D30, M57D30 (306D2) and M57N2 (306D3): the same commercial label can conceal two entirely different units. The engine code stamped on the block — not the engine capacity or the quoted power output — is the only reliable way to identify the correct compatible gearbox.

Key Points to Watch by Model

The 3 Series accounts for the largest number of references (17), followed by the 1 Series (12) and the X1 and X3. On the X1 and 2 Series Gran Tourer fitted with the 1.5d B37 or the 1.6d N47D16A, the gearbox is specific to the 3-cylinder engine and must not be confused with 2.0d units. For 2.0i and 2.0 engines, several codes overlap (B48B20, N20B20, N43B20, N46B20) but the fitment years differ: the engine generation determines the exact gearbox reference. If you are unsure about identification, the reference number of the original gearbox (visible on the casing) is the most reliable check.