27-62-00
ALL ú ú 02 Page 6 ú Nov 15/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500
MAINTENANCE MANUAL
CONTROL ROD DRIVE ARM
INPUT ARM SPEED
BRAKE LEVER
ACTUATOR
SHOE ASSEMBLY
SHOE PIN (4)
SHAFT
SHOE PIVOT PIN ALLOY STEEL SUPPORT
FRICTION BRACKET
QUADRANT
Lever Brake Mechanism
Figure 3
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27-62-00
ALL ú ú 02 Page 7 ú Nov 15/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
B.
C.
D.
A
737-300/400/500MAINTENANCE MANUAL
The lever brake mechanism consists of an input arm, a shoe assembly, a drive arm, a brake quadrant, a shaft, and a support bracket (Fig. 3). The lower control rod from the speed brake lever is attached to the support bracket which is mounted on the shaft. The shaft is supported in structure by two bearings. The outboard end of the shaft is splined for attachment of the speed brake forward drum. Shoe pins in the shoe assembly form a cluster above the brake quadrant in a rectangular layout. The shoe assembly is mounted on a pivot pin through a drive arm. The drive arm is fixed to the shaft and rotates with the shaft and drum. The brake quadrant and support bracket are held from rotating by the automatic speed brake lever actuator. A rotational force applied to the forward drum will be transmitted to the shoe assembly through the pivot pin. This force on the shoe assembly applies a shearing action on the brake quadrant through two diagonally opposed shoe pins producing a locking action. Forces applied to the forward drum in the opposite direction will have a locking action on the other diagonally opposed shoe pins. Motion of the input arm, caused by the speed brake lever rotation, initially unlocks the shoe assembly and then rotates the shaft. The input arm drives the shaft through flanges which contact the drive arm. When lever rotation is stopped, a compression spring in the shoe assembly returns the shoe pins to the locked position. Motion of the automatic speed brake lever actuator causes the support bracket and brake quadrant to rotate. This rotation is transmitted through the shoe assembly to the drive arm causing the shaft to rotate. The drive arm also drives the speed brake lever through the input arm. A load at the speed brake lever will unlock the shoe assembly and override the motion of the speed brake lever actuator.The speed brake lever actuator connects the lever brake mechanism support bracket to airplane structure. The actuator consists of a 28 volt dc electric motor, gearing, a displacement rod, nonjamming mechanical stops, and adjustable limit switches. The limit switches are bench adjusted to limit the stroke at the extended and retracted positions. The gearing prevents actuator motion due to external loads.The speed brake forward drum is splined to the lever brake mechanism. The drum is grooved for 1/8-inch cables and has integral cable guards. A switch cam is provided on the aft side of the drum. A switch actuator contacts the cam when the speed brake handle is down and locked. The speed brake arming switch, mounted on the actuator, controls automatic speed brake arming. A detent cam is provided on the forward side of the drum to provide an armed detent and a maximum inflight detent. A spring-loaded roller arm follows the cam and provides speed brake lever feel at these detents.
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