Manual gearbox

A manual gearbox is a box of gear pairs between the engine and the driven wheels. Each pair gives a different ratio: low gears let the engine spin fast while the wheels turn slowly, which multiplies torque for pulling away and climbing; high gears do the opposite for economical cruising. The driver chooses the ratio with the gear lever and uses the clutch pedal to disconnect the engine while changing.

Almost every modern manual is a constant-mesh design: all the gear pairs are permanently meshed, with the gears on the output shaft free to spin on bearings. Selecting a gear does not move the gears themselves; it slides a collar that locks one gear to the shaft.

• Press the clutch: the clutch plate separates from the flywheel and the input shaft stops receiving torque.
• Move the lever: a selector fork pushes a synchroniser sleeve towards the chosen gear.
• The synchroniser's brass cone rubs against the gear and matches its speed, so the dog teeth slide in without crunching.
• Release the clutch: torque flows from the input shaft, through the layshaft and the locked gear pair, to the output shaft and on to the differential.

The box is bolted to the back of the engine. In a front-wheel-drive hatchback such as the Swift it is a transaxle beside the transverse engine; in a Fortuner or a Tata truck it sits behind a lengthways engine with a propeller shaft to the rear axle. Trucks use the same idea with more ratios, often six to nine, sometimes with a splitter that doubles them.

What you notice: a direct, mechanical connection, the need to co-ordinate clutch and throttle at every stop, and the cheapest purchase and running cost of any transmission type.