32-41-00
 ALL  ú ú 05 Page 7 ú Oct 25/86
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 5.  Main Gear Brakes
________________
 A.  Tire to surface friction force for halting the aircraft is controlled through the application of hydraulic pressure to the multidisc brake. Rotors coupled to wheel/tire assemblies and stators attached to gear structure are pressed together by the action of hydraulic pistons causing the frictional force required to halt the aircraft. Automatic adjustment assemblies maintain correct brake element clearances. Wear indicators give visual warning of time to overhaul brakes. Hydraulic bleed ports are provided to assist in the overhaul.
 B.  The main landing gear brake is a multidisk type consisting of four rotating and five stationary frictional elements called rotors and stators, respectively (Fig. 5). Two of the stators, referred to as pressure plate and stator torque tube backing plate, are lined on one surface with 13 lining blocks per surface. The remaining stators are lined on both surfaces, with the same number of lining blocks per surface, and are notched on the inside diameter to enable them to fit and slide axially on the torque tube splines. The lining blocks are made from an inherently heat stable cerametallic material that will maintain its original strength and friction ability at incandescent temperatures. Each rotor is keyed to the wheel and consists of eight solid steel segments that are secured to a spider with keyed steel brackets. The brake carrier houses six actuating pistons and four automatic adjuster assemblies with return springs. The cylinders for the actuating pistons are all hydraulically interconnected through drilled passages in the carrier. Two bleeder valves are provided at the top of the carrier.
 C.  When the brakes are applied, hydraulic fluid under system pressure enters the inlet port of the brake, through a disconnect valve, and is distributed to the pistons. As the pistons move out under fluid pressure they push the pressure plate axially against the stack of stators and rotors so that the stack is compressed between the pressure plate and the torque tube backing plate, and rotational braking friction is developed.
 D.  As the brake elements wear, automatic adjustor pins prevent increases in running clearance. (Fig. 5). The adjuster pin and ball assemblies are attached to the pressure plate. Outward movement of the pressure plate pulls the adjuster pin, ball, and tube, causing the spring retainer to compress the adjuster spring. As the spring retainer bottoms in the housing the tube is restrained. Any additional travel in the pressure plate will pull the adjuster pin forcing the ball into the interference portion of the tube for a distance equal to lining wear. When the brakes are released the pressure plate is moved back by the return spring until the washer is pressed against the retaining ring. This allows the rotors to separate from the stators and rotate freely while maintaining a constant running clearance equal to the distance between the edge of the counterbore and the bottom of the retaining ring less the thickness of the washer.
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 32-41-00
 ALL  ú ú 07 Page 8 ú Feb 25/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 E.  Separate lining wear indicator pins are provided at two locations. Dimension L is set at brake manufacture or overhaul. Subsequent lining wear will cause dimension L, with brake pressure applied, to decrease to a point indicating when the brake must be removed for lining replacement.
 6.  Brake Accumulator System (Fig. 6)________________________
 A.  The brake accumulator stores energy for brake operation and assures instantaneous flow of fluid to the brakes. When fully charged, the accumulator holds a reserve of fluid under pressure sufficient for approximately six brake applications and for maintaining parking brake pressure.
 B.  The system has:
 (1)
accumulator, which has:

 (a)
air charging valve

 (b)
air charging gage

 (c)
transmitter and associated wiring to indicator on P2 panel.

 (2)
two one way check valves

 (3)
accumulator isolation valve

 (4)
Pressure relief valve.

 C.  
The accumulator is provided with an air or nitrogen charging valve and gage located with the accumulator to permit precharging. The accumulator is located on the lower aft wall of the right wheel well. Also included with the accumulator is a pressure transmitter connected electrically to the HYD BRAKE PRESS indicator on the lower P2 panel.
　
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