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A
747-400
MAINTENANCE MANUAL
SEEA
OUTER
CYLINDER
YOKE
STEERING
CYLINDERS
APEX
INNER
CYLINDER
LOWER TORSION
LINK
AFT
WHEEL
TRUCK
A
Body Gear Steering Mechanism
Figure 4
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747-400
MAINTENANCE MANUAL
A. Uncontrolled rotation of the inner shock strut cylinder is prevented by a single lower torsion link acting in conjunction with the body gear steering cylinders. The lower torsion link is connected to lugs on the aft portion of the truck beam. The upper ends of the steering cylinders attach to lugs on the shock strut outer cylinder. The lower ends of the steering cylinders join to meet the torsion link forming a flexible connection which allows normal vertical action of the shock strut.
10. Body Gear Truck Positioning Actuator (Fig. 5)
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A. The body gear truck positioning actuator is mounted on the upper, forward center of the wheel truck. The actuator piston rod points forward and is attached to lugs on the top of the truck beam, directly above the center of forward axle. The cylinder end containing a spherical bearing is pinned to the bottom, forward boss of the shock strut inner cylinder.
11. Truck Positioner Bypass Reducer Valve (Fig. 6)
_____________________________________
A. The truck positioner bypass reducer valve is a three-part hydraulic unit located in the upper wheel well area. It consists of a spool and sleeve assembly, poppet, guide, one ball and spring-type check valve and a cartridge type relief valve (Fig. 6). Pressure above 2200 psi causes the unit to completely open. The valve closes completely at 1900 psi. The valve supplies hydraulic fluid to the gear truck positioner actuator.
12. Body Gear Steering (Fig. 4)
__________________
A. Body gear steering provides directional control of the airplane during taxiing and towing. Two hydraulic cylinders attach to the aft side of shock strut by means of a yoke assembly. The lower ends of the cylinders join the lower torsion link which connects to lugs on the truck beam.
13. Body Gear Operation
___________________
A. Functional Description
(1) Because the inboard main gear struts attach directly to the body, they experience negligible side deflection on a nonturning operation Consequently, the load on any wheel axle is shared equally by its two wheels. This load distribution helps to equalize and reduce tire wear, improve braking efficiency on slippery runways, and minimize shock strut distortion and wear. All body gear trucks have full balanced brake torque rod geometry. The rods prevent partial transfer of truck load from aft wheels to forward wheels upon braking.
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747-400
MAINTENANCE MANUAL
BARREL END
ROD END (ON
END OF TRUCK BEAM)
VALVE
Truck Positioning Actuator
Figure 5
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