converter clutch. Later they were able to control transmis-
sion shifting and internal pressures. Early electronic trans-
missions were simply updated hydraulic models, with only
a few functions being performed by the computer and the
output solenoids. Modern transmissions and transaxles are
fully controlled by the computer.
Automatic Transmission and
Transaxle Components
Automatic transmissions are made of many separate
components and systems. See Figure 1-11 and 1-12. Some
of the most important automatic transmission and transaxle
components are discussed in the following sections. These
components will be covered in more detail in later chapters.
Fluid Coupling/Torque Converter
Fluid couplings and torque converters are fluid-filled
units installed between the engine’s crankshaft and the
transmission. They consist of two sets of blades. One set of
blades is driven by the engine, and the other set of blades
is connected to the transmission’s input shaft. The blade set
connected to the engine is called the impeller, and the
blade set connected to the input shaft is called the turbine.
See Figure 1-13. A hydraulic pump in the transmission
forces fluid into the converter. Inside the converter, the
fluid is spun by the impeller blades. As the fluid is thrown
from the impeller blades, it strikes the turbine blades. See
Figure 1-14. Power is transmitted from the impeller to the
turbine through the fluid. When the vehicle is stopped, the
fluid from the impeller continues to strike the turbine, but
the fluid allows enough slippage between the impeller and
the turbine to prevent engine stalling.
Chapter 1 Introduction to Automatic Transmissions and Transaxles 17
Passing gear
solenoid switch
Figure 1-9. 1958 Chevrolet Turboglide transmission.This trans-
mission used an all-aluminum case.
Figure 1-10. A linkage-mounted switch energizes the passing
gear solenoid on a 1963 Pontiac Tempest.
Flexplate
Shift
lever
Oil
pan
Valve body
(hydraulic
control valves)
Case
Output
shaft
Driveline
slip yoke
Extension
housing
Planetary gearsets
Bands
Clutches
Input shaft
Crankshaft
Torque converter
Converter housing
Engine
Figure 1-11. This diagram shows the major components of an automatic transmission. Note how the components fit in
relation to each other.