TM 9-2320-272-24-1
1-14. LOCATION AND DESCRIPTION OF MAJOR COMPONENTS (Contd)
Key Item and Function
1 LIFTING SHACKLE(S) - Permit vehicle to be towed by another vehicle or used for tiedown
attachment when transporting vehicle.
2 ENGINE - There are two different Cummins model engines used, the NHC 250 (M939/A1 series
vehicles) and 6CTA8.3 diesel (M939A2 series vehicles), which provide mechanical power to the
vehicle and engine-driven subsystems.
3 TRANSMISSION - The Allison MT546CR automatic, used on all M939/A1/A2 series vehicles,
adapts the engine's output for a varying range of operating speeds.
4 PRIMARY AND SECONDARY AIR RESERVOIRS - Provides storage of compressed air and
isolation between air subsystems.
5 TRANSFER CASE - Directs the engine and transmission output to the specified axles and/or
auxiliary equipment.
6 WET TANK RESERVOIR - Provides reserve storage of compressed air created by the air
compressor or external source when demand is low and releases it when required. This lessens the
cycling of the engine-driven air compressor.
7 REAR PROPELLER SHAFT(S) - Transmits power between transfer case and forward-rear axle
assemblies, and between forward-rear and rear-rear axles assemblies.
This allows components that cannot maintain precision alignment to transfer power from one point
to another, without undue stress or breakage.
9 SERVICE BRAKE CHAMBER - Mechanical brake actuator that is activated by applying air
pressure to an expandable cylinder, causing it to apply braking force to the brakedrum.
springs, and seats that support the rear vehicle weight.
11 SPRING BRAKE CHAMBER - Mechanical brake actuator that is spring-loaded to apply brakes
when air is low or not present. During normal vehicle operation, air piston counteracts the spring
tension and allows the brakes to release. Spring brakes can be bypassed by pushing in the spring
brake OVERRIDE switch on the instrument panel, or released using procedures found in TM 9-2320-
272-10.
12 TOWING PINTLE - Provides a secure quick-connect/disconnect for towing vehicles or equipment.
and provide a straight-through connection to power additional propeller shafts.
14 FUEL TANK(S) - Provides storage of fuel.
15 SPARE TIRE CARRIER - Stores spare tire.
D a v i t - Used to load and unload spare tire on M923/A1/A2, M925/A1/A2, M927/A1/A2,
M928/A1/A2, M931/A1/A2, and M9321/A1/A2 model vehicles.
Winch and Swinging Davit - Used to load and unload spare tire on M934A1/A2 model vehicles.
Optional kit is available for M934 model vehicle.
Hoist and Lifting Eye - Used to load and unload spare tire on M929/A1/A2, M930/A1/A2, and
M934 model vehicles. Optional kit is available to support dump bed in semi-raised position during
tire removal.
Vehicle Crane - Used to load and unload spare tire on M936/A1/A2 model vehicles. NOTE: On
M936/A1/A2 model vehicles, remove spare tire prior to changing tire, and install tire in spare tire
carrier after tire change is complete. Operation of crane and/or vehicle engine while vehicle is on
jacks may cause the vehicle to slip off jack.
16 AIR CLEANER - Filters air before it enters the intake manifold or turbocharger and collects dust in
removable section of filter canister.
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