The Fiat M40, also designated C546, is a heavy-duty 6-speed manual transmission developed for transverse front-wheel-drive light-commercial applications. It is used primarily in the large Fiat/PSA van platform and is designed for high-torque diesel engines, with a capacity of approximately 400 Nm.
Specification: 6-speed manual • Fiat M40 / C546 • Transverse installation • Front-wheel drive • Cable-operated gear selection • Dry single-plate clutch • Fully synchronised manual gearbox • Integrated differential • Approximately 400 Nm maximum torque • Manual and Comfort-Matic/MTA robotised versions • Multiple gear-ratio and final-drive configurations.
The M40 is fitted primarily to selected Fiat Ducato, Peugeot Boxer and Citroën Jumper/Relay applications, particularly higher-output diesel versions. Ratios and components vary by engine and production version, so the VIN, complete gearbox code and individual component identification should always be confirmed before ordering replacement parts.
Common Faults
Common M40 problems include shaft-bearing wear, synchroniser wear, gear wear, selector problems and internal corrosion/wear of the synchroniser and gear assemblies. Symptoms can include gearbox whine, difficult or crunching gear changes, excessive drivetrain noise and 6th-gear noise.
Diagnosis should include oil level and condition, shaft bearings, gears, synchronisers, selector components, differential and clutch operation before the gearbox is dismantled.