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TM 9-8000
results in the entire planetary gearset rotating as a solid
the solenoid are two electromagnetic coils: the pull-in and
the hold-in coils. The pull-in coil initially actuates the sun
gear locking pawl. To do this, the pull-in coil must be
b.  Overdrive (Fig.  26-6).  When the operator
very powerful and, therefore, will use a lot of electic
desires overdrive, the control lever is moved to the
current. Because of this, the pull-in contacts are situated
overdrive position. This lever movement slides the sun
to deenergize the pull-in coil when the solenoid is
gear out of mesh with the pinion carrier, allowing the
actuated fully.  The hold-in coil, which is somewhat
planetary gearset to operate. The control system of the
lighter, then is utilized to hold the solenoid in the fully
overdrive unit will semiautomatically select between the
actuated position for the duration of overdrive operation.
two following modes of operation:
Solenoid Relay.
The solenoid relay
(1) At speeds below approximately 30 mph, the
provides power to the solenoid whenever a signal current
solenoid pawl is disengaged. This combination results in
is applied to it from the signal circuit.
all planetary gearset members being free to rotate. The
result will be direct drive through the roller clutch when
(3) Governor. The governor is a centrifugal-
engine torque is applied.  When the accelerator is
type switch that completes the single circuit to the
released, the roller clutch will retract and the vehicle will
solenoid  relay  whenever  the  vehicle  reaches
approximately 30 mph (48 kml/h).
(2) At speeds above approximately 30 mph (48
(4) Rail Switch. The rail switch interrupts the
kmlh), the solenoid is energized and the pawl tries to
signal circuit whenever the overdrive unit is locked out,
engage the sun gear plate. The pawl will be blocked by
preventing engagement.
the bulk ring, however, until the engine power flow is
interrupted (the operator momentarily releases the
Throttle Switch.
The throttle switch
accelerator).  As the accelerator is released, the sun
interrupts the signal circuit whenever the accelerator is
gear, which is being driven by the pinions, slows down
pressed to the floor, allowing the operator extra power.
and reverses direction as the overdrive unit begins to
The throttle switch, in conjunction with the ground-out
freewheel. This reversal of the sun gear causes it to pull
contacts, also will disable the engine temporarily. This
back the bulk ring, allowing the pawl to engage the sun
interruption of engine power is necessary to allow the
gear plate, locking the sun gear. The locking of the sun
locking pawl to disengage from the sun gear wheel. The
gear results in the planetary gearset causing the
process of disengaging the overdrive unit by the action of
overdrive effect.
the throttle switch takes only a fraction of a second.
b. Reverse Lockout. The linkage of the overdrive
26-9. Overdrive Control System.
lockout mechanism is integrated with the transmission so
that the lockout is engaged whenever the transmission is
a.  General (Fig.  26-7).  The overdrive unit is
shifted to reverse.  This arrangement is necessary
semiautomatically operated by an electrical control
because the roller clutch will not drive the vehicle in
system that is influenced by vehicle speed, throttle
position, and the position of the lockout control lever.
The following components make up this system:
(1) Solenoid. The solenoid, when energized,
operates the sun gear locking pawl. Inside


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