D.  
Tires and Wheels

________________
 (1)  
The tires and wheels support the airplane during ground operations. Four tires and wheels are installed on each main gear and two on the nose gear (see wheels and tires description and operation).

 E.  
Brake Temperature Monitoring System

___________________________________
 (1)  The brake temperature monitoring system provides a means for the flight crew to monitor the temperature of the brakes to help them avoid being overheated during braking operations (see brake temperature monitoring system description and operation).
 

 32-40-00
 ALL  ú ú 01 Page 1 ú Jan 20/98
 
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757 MAINTENANCE MANUAL
 HYDRAULIC BRAKE SYSTEM - DESCRIPTION AND OPERATION
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 1.  General_______
 A.  The hydraulic brakes are controlled manually by applying foot pressure to the captain's and/or first officer's brake pedals, or automatically by the autobrake system (Ref 32-42-00). In the manual mode of operation, which is covered in this section of the maintenance manual, the four brakes on the left gear are operated by the pilot's left pedal(s) and the four brakes on the right gear are operated by the pilot's right pedal(s). The captain's and first officer's brake pedals are joined together by linkage so that braking force will be the combined force applied to the pedals by both pilots.
 B.  The hydraulic brake system includes the main landing gear brake assemblies (8 places), mechanical control linkage from the pilot's foot pedals to the brake metering valve modules (left and right sides), hydraulic valves (accumulator isolation, alternate brake selector, brake metering valve modules, parking brake pressure accumulator, check valves, wheel brake (de-spin) actuator, hydraulic lines and pilot's brake system indications.
 (1)  
The carbon brakes are multiple disk rotor-stator type units that are activated hydraulically.

 (2)  
The pedal and quadrant linkage consists of the pilot's foot pedal mechanism (bellcranks, pushrods, quadrants) which connects to the left and right metering valve modules by cables running aft through the floor beams. Two sets of cables are installed, one on each side, and are connected to the respective left or right metering valve module.

 (3)  
The brake hydraulic system is normally powered by the right hydraulic system, however, if right system pressure is lost, the left system pressure is automatically selected by the alternate brake selector valve to operate the brakes. A brake accumulator is provided in the event loss of both right and left hydraulic systems occurs. A limited number of brake applications (1 to 2) can be accomplished using the accumulator source. A reserve source of brake hydraulic power can be selected if other sources become inactive. The reserve source consists of one electric motor-driven pump and a dedicated supply of hydraulic fluid in the right hydraulic system used for brakes.

 (4)  
Hydraulic system indications provided to the pilots include a brake system pressure gage, a low hydraulic brake pressure light, and Engine Indicating and Crew Alerting System (EICAS) caution messages (Ref 31-41-00).

 C.  
The parking brake system is included as a integral part of the hydraulic brake system and provides a means of keeping brakes on without applying constant foot brake pedal pressure (Ref 32-44-00).

 32-41-00
 ALL  ú ú 01A Page 1 ú Mar 15/87
 
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757
MAINTENANCE MANUAL

 D.  The antiskid system operates through the hydraulic brake system to prevent skids during braking. During normal braking, pressure is unmodified by the antiskid valves. However, if one or more wheels enter a skid condition, the antiskid valves will automatically reduce hydraulic pressure to the affected brakes. When the skid has been averted, the antiskid valves will revert to normal, and allow normal braking to continue. The antiskid and autobrake systems are combined into one maintenance manual section (Ref 32-42-00).
 E.  The brake temperature monitoring system is installed to monitor the temperature of each of the eight brakes and aid the pilots in avoiding an overheat condition when the brakes are being operated (Ref 32-46-00). Brake temperature values are displayed on the status mode of the EICAS system (Ref 31-41-00).
 F.  Gear retract braking, to stop the wheels from spinning prior to them entering the wheel well after take off, is accomplished from the gear-up hydraulic pressure line. This pressure actuates the autobrake (de-spin) actuators on the left and right alternate brake metering valves which in turn actuates the brakes.
　
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