INTRODUCTION 777 SERVICE MANUAL
1-52 Published 10-01-2012, Control # 045-08
LOAD DRUM (FREE FALL MODE)
See Figures 1-36 and 1-37 for following procedures.
Drum pawl must be disengaged before attempting to lower a
load in free fall.
The following description is for the front drum if the crane has
free fall and is operating in free fall mode. Operation of the
rear drum is identical.
The PC will not allow a drum to be switched to free fall mode
until its working brake pedal is latched down, the drum
parking brakes switched off, and the free fall is confirmed
and selected.
The PC automatically applies the park brakes only when the
load drum park brake switch is placed in the park position.
Always park load drums not in use and fully apply and latch
the working brake for the load drum being used.
When the working brake pedal is fully depressed and
latched, front drum parking brake switch is off or in closed
position and the operator has selected and confirmed free
fall at switch, full pressurized system flow path from pump is
blocked at working brake pedal valve permitting the release
of the coil spring at band brake cylinder to expand and apply
pressure against the drum while its exhausting oil goes back
to tank through working brake pedal valve. Free fall safety
pressure switch at this time opens a circuit to the PC which
allows the front drum to be placed into free fall mode and free
fall drum system light on the front console is illuminated
indicating the front drum to be in free fall mode.
FIGURE 1-36
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