BOLT 
WASHER 
(4 LOCATIONS) 
PRESSURE 
SWITCH  ELECTRICAL 
HYDRAULIC  CONNECTOR 
LINE 
ELECTRICAL 
CONNECTOR 

PRESSURE SWITCH  ELECTRICAL CONNECTOR 
SOLENOID VALVE 
FWD HYDRAULIC LINE  HYDRAULIC LINE SOLENOID VALVE ASSEMBLY 
B  2 
2  TEXTRON MODULES 

Autobrake Pressure Control Module Installation
Figure 401 (Sheet 2)

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G25667
A 
737-300/400/500MAINTENANCE MANUAL
 (q)  Remove the pressure from hydraulic systems A and B
 (AMM 29-15-00/201).
 (r)  Remove the DO-NOT-CLOSE tags and close the circuit breakers
 that follow:
 1)  P6 Panel
 a)  AUTOSLAT circuit breakers
 2)  P6-3 Panel
 a)  AUTOBRAKE CONTR
 (s)  Remove the electrical power if it is not necessary
 (AMM 24-22-00/201).

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 1.

2.

3.

4.

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737-300/400/500MAINTENANCE MANUAL
 PARKING BRAKE SYSTEM - DESCRIPTION AND OPERATION
________________________________________________
General (Fig. 1)
_______
 A.  The parking brake system is used to apply and hold brake pressure through the metering valves when the airplane is parked or moored.
 B.  The parking brake system is composed of:
 (1)
Parking brake lever, holding pawls and lever linkage

 (2)
Parking brake lights, switch and associated wiring

 (3)
Parking brake valve, switch and associated wiring

 CAUTION: PARKING BRAKES SHOULD NOT BE SET FOLLOWING A HIGH ENERGY STOP.
_______ HIGH ENERGY STOPS ARE DEFINED AS A REFUSED TAKE OFF OR ANY STOP OTHER THAN NORMAL. UNDER STATIC PRESSURE, HOT BRAKE SURFACES TEND TO FUSE TOGETHER. THEREFORE, AFTER A HIGH ENERGY STOP, OR FOLLOWING TOUCH AND GO STOPS, A COOLING PERIOD OF 40 TO 60 MINUTES SHOULD BE ALLOWED BEFORE THE PARKING BRAKE IS SET.
 C.  The parking brake uses the existing brake system. Application is made by foot and hand operated linkage and utilizes pressure from the B hydraulic system or the accumulator (See Fig. 2). A parking brake shutoff valve located in brake return flow lines prevents the normal decay of pressure through the antiskid valves. A red light beside the parking brake lever on the center aisle stand warns of parking brake application when illuminated.
Parking Brake Linkage (Fig. 1)
_____________________
 A.  Application of the parking brake requires a full and simultaneous application of left and right foot pedals. This allows clearance for the parking brake lever linkage to be moved, rotating a lock-shaft fitted with pawls. The pawls rotate into a pin holding position with brake pedal linkage. Thus positioned, the pawls hold the brake metering valves open porting pressure to the brakes.
Parking Brake Light (Fig. 1)
___________________
 A.  The red parking brake light on the control stand is illuminated by closing of a switch caused by the rotation of an outboard lever on the parking brake jackshaft at parking brake application. The microswitch also completes a circuit to actuate the parking brake shutoff valve closed.
Parking Brake Shutoff Valve (Fig. 1 Sheet 2)
___________________________
 A.  The parking brake shutoff valve is installed in a common return line in the main wheel well between the four antiskid control valves and a system return line and prevents pressure bleed off when parking brakes are set.
 B.  The parking brake shutoff valve is a 28-volt dc motor-operated ball-type valve. When parking brakes are set or released, the parking brake switch will actuate to energize the shutoff valve to closed or open position.
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