CONFIDENTIAL TIBU4507-03
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TECHNICAL INFORMATION BULLETIN |
June 22, 2005 |
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Off-Highway Truck |
797 (5YW1-Up) 797B (JSM1-199) |
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Component Code 4263 |
SUBJECT: Brakes May Not Function Correctly Under Certain Conditions on Certain Off-Highway Trucks
PROBLEM: The ISO 3450 Brake System Performance Standard, requires that a warning must alert the operator when the stored energy level in the service brake accumulators drops below a certain level. Under some hot ambient conditions the requirement of having a minimum of one brake application, after the warning has sounded, is not being achieved. If the brake system pressure continues to drop, at some point the parking brake will automatically apply in order to stop the machine.
SOLUTION:
Reduce the pre-charge pressure for the 214-2008 and 168-8364 service brake accumulators. Refer to the table below for the proper pre-charge pressures.
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Relationship Between the Service Brake Accumulator Pre-Charge Pressure and the Ambient Temperature |
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Temperature |
Pre-charge Pressure |
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-7° C (20° F) |
6201 kPa (900 psi) |
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-1° C (30° F) |
6339 kPa (920 psi) |
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4° C (40° F) |
6477 kPa (940 psi) |
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10° C (50° F) |
6580 kPa (955 psi) |
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16° C (61° F) |
6718 kPa (975 psi) |
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21° C (70° F) |
6895 kPa (1000 psi) |
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27° C (81° F) |
7028 kPa (1020 psi) |
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32° C (90° F) |
7166 kPa (1040 psi) |
At the pre-charge pressures listed above, the accumulator system will take longer to purge after the engine is turned off. Therefore, after the engine is turned off, there may be residual pressure in the brake accumulator system. Ensure that the guidelines for "Pressurized Items" that is listed in SENR7733, General Service and Repair Safety Information, are followed. Action is currently being taken to ensure that the brake accumulator system is properly purged when the engine is turned off.
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