NOTE: Put the bleed plug in a clean bag and keep them for
____ installation when you complete the test.
 S 425-091
 CAUTION: DO NOT TIGHTEN THE BRAKE PRESSURE GAGE TO MORE THAN 110
_______ POUND-INCHES. IF THE BRAKE PRESSURE GAGE IS TIGHTENED TO MORE THAN 110 POUND-INCHES, DAMAGE TO THE BRAKE CAN OCCUR.
 (7)  
Install a pressure gage on a brake.

 S 615-060

 (8)  
Make sure the brake hydraulic accumulator has the correct precharge pressure (AMM 12-15-09/301).

 S 615-061

 (9)  
Make sure the hydraulic pressure surge accumulators have the correct precharge pressure (AMM 12-15-11/301).

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747-400 MAINTENANCE MANUAL
 F. Parking Brake Hold Check
 S 865-064
 (1)  
Pressurize hydraulic system 4 (AMM 29-11-00/201).

 (a)  
Make sure that the HYD BRAKE PRESS gage on the P1-4 panel shows 2900-3150 psi.

 (b)  
Make sure that the system No. 4 wing and/or the tail FLT CONTROL SHUTOFF switches on the P461 panel is in the ON position.

 (c)  
Set the parking brake.

 (d)  
Make sure the pressure gage on the brake and the HYD BRAKE PRESS gage on the P1 panel show the same pressure (|100 psi).

 (e)  
Make sure the pressure in not less than 2800 psi.

 (f)  
Write down the brake pressure.

 (g)  
After 10 minutes, remove pressure from hydraulic system No. 4.

 NOTE: Hydraulic systems No. 1 and 2 must not be pressurized.
____ Keep the brakes pressurized with the brake accumulator only.
 (h)  Do a minimum of one of these parking brake pressure tests:
 NOTE: In all cases the pressure drop 10 minutes after
____ hydraulic pressure is removed must be written down and must be less than 275 psi.
 NOTE: Normally, passing one of these tests will supply
____ parking for at least 8 hours. The longer test times give a higher level of confidence should the leakage characteristic not be normal.
 1) After 10 minutes, the parking brake pressure must not decrease more than 275 psi. 2) After 30 minutes, the parking brake pressure must not decrease more than 600 psi. 3) After 1 hour, the parking brake pressure must not decrease more than 800 psi.
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747-400
MAINTENANCE MANUAL

 4)  After 2 hours, the parking brake pressure must not decrease more than 1000 psi.
 (i)  
If the parking brake pressure decreases faster than permitted, do the applicable Fault Isolation Procedure (FIM 32-44-00/101).

 (j)  
If the parking brake pressure drop is greater than allowed, fault isolation may be delayed and the airplane dispatched if this parking brake test is passed. 1) Pressurize hydraulic system 4 (AMM 29-11-00/201). 2) Set the parking brake. 3) Immediately remove the pressure from hydraulic system

 No. 4. 4) After 10 minutes, parking brake pressure is not less than 825 psi.

 (k)  
Release the parking brake.

 G.  
Put the Airplane Back to Its Usual Condition

 S 865-076
 (1)  
Remove the power from hydraulic systems 1, 2 and 4
 (AMM 29-11-00/201).

 S 865-077

 (2)  
Make sure that the parking brake is released.

 S 085-078

 (3)  
Remove the pressure gage.

 S 435-079

 (4)  
Install a brake bleeder assembly at the brake.

 NOTE: The brake bleeder assembly has a bleeder valve installed in a
____ bleeder adapter fitting. The bleeder adapter fitting is installed in the brake assembly. To bleed the brake, open and close the bleeder valve.
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