The Sliding-Mesh Gearbox: Choosing a Ratio With the Engine Running

In 1891 the Paris firm of Panhard et Levassor laid out a car the way cars stayed for a century: engine at the front, a clutch behind it, then a gearbox, then the drive to the rear wheels. Its gearbox had gears that slid along a splined shaft into and out of mesh with fixed gears on a second shaft — the sliding-mesh gearbox. Émile Levassor is often quoted describing it as brutal, but it works. It exists because an engine only pulls well over part of its speed range. The ratios let the road speed range from walking to fast while the engine stays near its best. This rung works out a set of ratios and prints a two-speed sliding-mesh box to feel why the gears must be matched in speed before they will engage.