Copyright by Goodheart-Willcox Co., Inc.
188 Automatic Transmissions and Transaxles
Figure 9-2. (continued) C—Vane-type oil pump. This design also includes a built-in converter clutch and pressure regulator valves.
Figure 9-3. This transmission has a separate motor driven
hydraulic pump. There is no engine driven pump. (Toyota)
C
system through the outlet as the internal elements come
back together.
A few transmissions have a separate motor-driven
pump to provide pressure. The pump is connected to the
transmission hydraulic system by hoses, Figure 9-3. The
vehicle ECM varies pump drive motor speed to provide the
correct oil pressure under various loads.
Note that modern transmissions use only one pump,
which is driven from the engine. However, many older
transmissions used two oil pumps. The front pump was
driven by the engine through the converter. The rear pump
was driven by the transmission output shaft. The rear pump
turned whenever the vehicle was moving. It developed
pressure for push starting and for providing lubrication to
the transmission if the vehicle was being towed.