The Hydraulic system is a complex maze of passages and tubes that sends transmission
fluid under pressure to all parts of the transmission and torque converter.
The diagram below is a simple one from a 3-speed automatic from the '60s. The newer systems
are much more complex and are combined with computerized electrical components.
Transmission fluid serves a number of purposes including: shift control,
general lubrication and transmission cooling. Unlike the engine, which uses
oil primarily for lubrication, every aspect of a transmission's functions are
dependant on a constant supply of fluid under pressure. This is not unlike
the human circulatory system (the fluid is even red) where even a few minutes
of operation when there is a lack of pressure can be harmful or even fatal
to the life of the transmission. In order to keep the transmission
at normal operating temperature, a portion of the fluid is sent through one
of two steel tubes to a special chamber that is submerged in anti-freeze
in the radiator. Fluid passing through this chamber is cooled and then returned
to the transmission through the other steel tube. A typical transmission
has an average of ten quarts of fluid between the transmission, torque converter,
and cooler tank. In fact, most of the components of a transmission
are constantly submerged in fluid including the clutch packs and bands.
The friction surfaces on these parts are designed to operate properly only when
they are submerged in oil. |
