MAINTENANCE OF M939 SERIES VEHICLES - OD1661 - LESSON 1/TASK 1
reaches 185 F. The cooling system is equipped with a surge tank that
has a cap pressure of 14 psi. The radiator used in this system is of
the crossflow type and the fan measures 26 inches.
d.
Transmission.
The M939 family of vehicles uses the MT654
transmission.
The transmission contains between 4.25 gallons
(without a power takeoff (drain and refill)) and 6.25 gallons (with a
power takeoff)(dry)).
What this means is that if a vehicle is
received from the factory and is equipped with a power takeoff, it
will take 6.25 gallons of OE/HDO 10 transmission oil to fill the
tank.
The transmission has a normal operating temperature range of
120 F to 220 F, with maximum temperature being 300 F.
e.
Compressed Air and Brake System Operation.
The compressed air
and brake system, common to all models, takes filtered air,
compresses it, and supplies it to various components that enable the
operator to slow down or stop the vehicle. This system also supplies
compressed air to air-actuated accessories throughout the vehicle.
The components of this system are as follows:
(1) Front Emergency Coupling (figure 8 on the following page).
When the vehicle is being towed, the coupling receives compressed air
from the towing vehicle's brake system to charge its own brake
system.
(2) Front Service Coupling. When the vehicle is being towed, the
coupling is connected to the towing vehicle so that the brake systems
of the two vehicles work together.
(3) Brake Chambers.
Converts air pressure to mechanical force
which applies front and rear brakes.
(4) Spring Brake Release Control Valve.
Pushed in to release
spring brakes independently of the mechanical handbrake. The control
is also used to release spring brakes in order to test and adjust the
mechanical brake.
(5) Primary Air Reservoir.
Stores air pressure so that if the
constant pressure system fails or the engine stalls, the operator can
make normal brake application before running out of air.
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