Seals are used at moving parts, such as the torque
converter, drive shaft, and various internal rotating parts.
They are also used as sliding pressure seals at the band ser-
vos and clutch apply pistons. Figure 1-33 shows a servo
seal. Some seals are used to seal stationary parts. These
seals are usually called O-rings.
A seal ring is a special type of seal that prevents leaks
in pressure passages between parts that rotate in relation to
each other, Figure 1-34. For example, oil pressure from the
valve body may be directed through a stationary support to
a rotating clutch drum. Seal rings keep the pressure from
being lost.
Manual Linkage and Throttle Linkage
To provide drive input, two types of linkage are used.
The manual linkage connects the shift lever to the manual
valve inside the transmission or transaxle. The linkage can be
a cable or a series of rods and levers. Cables are commonly
used on modern vehicles. Figure 1-35 shows a commonly
used manual linkage arrangement. The shifter is mounted
on the steering column or on a center console. In the Park
position, the manual linkage operates a park lock inside
the transmission or transaxle. The park lock is a lever that
engages a toothed wheel on the output shaft, Figure 1-36.
When the park lock is engaged, the vehicle cannot roll.
Throttle linkage connects the engine’s throttle plate to
the transmission’s throttle valve. On some transmissions,
throttle linkage is used to apply extra pressure for a forced
downshift (or passing gear). On other transmissions and
transaxles, the throttle linkage controls all shift speeds. On
some older cars, a vacuum modulator controlled shift speeds.
Vacuum modulators are still used on a few vehicles. Most
modern throttle linkage is cable operated, Figure 1-37. On
newer vehicles, the computer controls shift speeds and
throttle linkage has been eliminated.
26 Automatic Transmissions and Transaxles
TFP manual valve
position switch
assembly
1-2 and 2-3 shift
solenoid valves
1-2 and 2-3 shift
solenoid valves
Output speed
sensor
Input speed sensor
Pressure control
solenoid
TCC control
PWM solenoid
Figure 1-30. Sensors and solenoids used on a modern electronically controlled transaxle. The sensors provide input signals to the
computer, which in turn sends output signals to the solenoids. (General Motors)