D.  
The brake system contains these components:

 -Brake/rudder pedals
 -
Brake pedal bus (one left and one right)

 -
Brake cables

 -
Brake metering valve and control quadrant (one left and one right)

 -
Alternate source selector valves (number 1 & number 2)

 -
Alternate brake return valve

 -Accumulator isolation valve
 -Brake system pressure switches (Alternate Brake System and Hydraulic System 4)
 -Hydraulic brake disconnect (one for each brake)
 -Landing gear brake (one for each main gear wheel, 16 total)
 -
Hydraulic accumulator with air charging valve, direct reading pressure gage, brake pressure transmitter and HYD BRAKE PRESS gage

 -
Hydraulic pressure surge accumulator with charging valve and direct reading pressure gage.

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 32-41-00
 ALL  ú ú 01 Page 1 ú Feb 18/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 2.  Brake Pedal Bus (Fig. 1)
_______________
 A.  Manual operation of the brakes is started by pushing in on the rudder pedals (referred to as brake in this section). Force on the end of the brake pedals causes the pedals to turn on a shaft. This movement is transmited to brake-pedal-bus-crank assemblies through a set of bell cranks and push rods. One brake-pedal-bus-crank assembly is installed forward of the captain's pedals and one forward of the first officer's pedals. The brake-pedal-bus-crank assembies are connected together by bus rods so that force on the the captain's or the first officer's left pedal will turn only the left crank assembly and force on the captain's or first officer's right pedal will turn only the right crank assembly.
 B.  A pushrod connects the brake-pedal-bus-crank assembly forward of the captain's pedals to the left-brake-cable-control quadrant. A pushrod connects the brake-pedal-bus-crank assembly forward of the first officer's pedals to the right-brake-cable-control quadrant.
 C.  Cables connect the left-brake-cable-control quadrant to the left-brake-metering-valve-control quadrant in the left-wing-gear wheel well. Cables connect the right-brake-cable-control quadrant to the right-brake-metering-valve-control quadrant in the right-wing-gear-wheel well.
 D.  In this way force on the captain's or the first officer's left brake pedal will operate only the brakes on the left side of the airplane. Force on the captain's or first officer's right brake pedal will operate only the brakes on the right side of the airplane.
 E.  You can remove and install the brake-pedal-bus crank assembly using a procedure in this section. Steps to adjust the linkage are included. It is not necessary to reduce tension on the control cables when removing, installing or adjusting the brake-pedal-bus assemblies.
 3.  Alternate-Source-Selector Valves (Fig. 2)
________________________________
 A.  Two alternate-source-selector valves automatically select the source of hydraulic pressure to the alternate-brake-metering valves if there is a loss of pressure in hydraulic system number 4. Alternate-source-selector valve 1 supplies pressure from hydraulic system number 1 and alternate-source-selector valve 2 supplies pressure from hydraulic system number 2.
 B.  Alternate-source-selector valve 2 is on the rear spar of the left wing near the fuslage and alternate-source-selector valve 1 is on the inboard bulkhead of the right body gear wheel well.
 C.  Each valve has five ports. The pressure port "P" gets pressure from the hydraulic system. The brake pressure port "BP" supplies pressure to the brake system. The brake return port "BR" gets fluid from the brake return lines. The return port "R" sends fluid back to the hydraulic system. Control ports "C1, C2 and C3" use hydraulic pressure from other sources to open and close the pressure and return ports of the valve.
 D.  Alternate-source-selector valve 1 is connected to the hydraulic systems as follows:
 -C1 is connected to the return line of hydraulic system 1.  Thus pressure at this port is always low
 -C2 is connected to hydraulic system number 4
 -C3 is connected to landing gear retraction pressure
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