TM-9-2320-272-10
TRUCK, 5-TON, 6X6, M939, M939A1, AND M939A2 SERIES TRUCKS (DIESEL)
TECHNICAL MANUAL; OPERATOR'S MANUAL
SEPTEMBER 2004
CHANGE 2
TM-9-2320-272-10 - Page 83 of 481
TM 9-2320-272-10
1-66
Change 2
B
LIMITING VALVE
–
Serves three functions:
• Regulates signal air pressure going to front brake chambers so rear brakes
are applied first.
• Regulates signal air pressure to front brake chambers so operator has
control over amount of braking.
• Releases air pressure in front brake chambers directly to vent in the valve
when brake pedal is released.
C
FRONT BRAKE CHAMBERS
–
Converts air pressure to mechanical force
which applies front service brakes.
1-20. COMPRESSED AIR AND BRAKE SYSTEM OPERATION (Contd)
(2) The primary constant pressure system is made up of the following
components:
D
PRIMARY RESERVOIR LOW AIR PRESSURE SWITCH
– Activates
warning buzzer and warning light when air pressure goes below 60 psi (414 kPa).
NOTE
Vehicles equipped with ABS will have a
LQ-2 valve inplace of limiting valve or
front brake valve to control air pressure to
front brake chambers.
A
PRIMARY AIR PRESSURE GAUGE
–
Indicates amount of air pressure in
primary system.
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