The M40 reference article from the English Wikipedia on 24-Apr-2004
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M40

M40 is a four speed gearbox from Volvo used in the B18 engined versions of both the Volvo PV and the Volvo Amazon. Also fitted to Volvo 140 and Volvo 240 versions built for the 1975 model year. A version fitted with the British Laycock D'Normanville overdrive called the M41 and a strengthened version called M400 was also made.