INTRODUCTION 777 SERVICE MANUAL
1-42 Published 10-01-2012, Control # 045-08
Drum Pawl Engage
The following description is for the front drum only. The rear
drum actuator orientation is the opposite, as well as its
actuation.
When a selected pawl switch is placed in the engage
position, a circuit is completed from the switch to the PC
ensuring no down command against the pawl. This keeps
the appropriate park brake solenoids de-energized (so the
brake remains applied) and prevents the corresponding
system’s hydraulic pump from stroking. In addition, a circuit
is completed to the pawl’s linear actuator, causing the front
drum actuator rod to retract (rear hoist drum actuator rod
extend), moving the pawl in (out). The drum is secure and
will not move in the lowering direction until its pawl switch is
disengaged and its park brake is released.
Drum Pawl Disengage
When a selected pawl switch is placed in the disengage
position, the park brake remains applied and a circuit is
completed to the pawl’s linear actuator. This causes the front
drum actuator to extend (rear hoist drum actuator rod retract)
and moves the pawl out (in).
FIGURE 1-28
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