The early 1980s were a strange, mad, dislocated time in the bicycle industry. At MAVIC they were developing carbon disc wheels, introducing the first neutral service motorbikes, getting into BMX and, weirdly, developing ultra-light aeroplanes.
Amidst all this manic activity, MAVIC somehow found time to develope their derailleurs. The plain, simple MAVIC 800 became the silver anodised MAVIC 801 and the grey 'hard' anodized MAVIC 851. The early MAVIC 801s and MAVIC 851s had the machined logos of the old 800, but they also were clearly designed to fit (non-French) Campagnolo dropouts and, crucially, had the new, signature, pulley cage with its adjustable pivot position.