Editing Manual transmission (section)

== Lubrication ==
{{more citations needed section|date=June 2020}}
Manual transmissions are lubricated with [[gear oil]] (or [[motor oil|engine oil]] in some vehicles) which must be changed periodically in some vehicles, although not as frequently as the fluid in an automatic transmission. Gear oil has a characteristic aroma because it contains added sulfur-bearing anti-wear compounds. These compounds are used to reduce the high [[sliding friction]] by the [[helical gear]] cut of the teeth (this cut eliminates the characteristic whine of straight-cut [[spur gear]]s). On motorcycles with "wet" clutches (clutch is bathed in engine oil), there is usually nothing separating the lower part of the engine from the [[Transmission (mechanical device)|transmission]], so the same oil lubricates both the [[engine]] and transmission.