In 1995 Allison Division
of GMC provided a
specification for a fluid
for use in
heavy duty truck, bus
and earth moving
vehicle hydraulic transmission, which they
manufactured. In these application, Type A and
Type A, Suffix A, ATF products,
described later, showed exceptionally
satisfactory performance.
However, the service in question did not demand all of the characteristics of ATF. Therefore, by reducing the
requirements of the fluid, less costly ingredients could be used.
The Allison specification was
designated Hydraulic Transmission Fluid, Type C. Many heavy duty motor oils in
the SAE 10W, SAE 20, and 20W viscosity classes in addition to some special
fluids, adequately met the specification. Subsequent service showed that fluids
in the SAE 10W class were most desirable. Consequently the specification was
modified and updated as of 1997. A designation Hydraulic Fluid Type C-1
was assigned to the new product.
It will
be found that other
manufacturers also recommend fluids of this type for their
heavy duty torque
converters.
