The most obvious answer to this question is that gear oil is generally
intended for use in manual gear boxes and transmission fluid is for automatic
transmissions. However, as is always the case with automotive lubricants, there
are exceptions to this rule. In order to fully understand what the differences
are between the fluids, we first have to take a look at the key differences
between gearboxes and transmissions.
Both a gearbox and a transmission essentially do the same job in that
they allow change of gears to control the speed, force and direction of
travel, but they achieve this in different ways and so require
different support fluids in order to operate properly.
Manual Gearbox
Manual gears operate based on a system of two shafts with gears which
mesh together after user input via the clutch and the gear stick. This means that the manual gearbox creates a
lot of heat, a lot of force and a lot of friction as the two moving objects
come together...
More after the jump...