THEORY OF OPERATION
GENERAL INFORMATION: M548A1
The M548A1, 6-ton tracked cargo carrier is powered by a liquid cooled 6V53, 210 horsepower diesel engine. The engine
power is converted to mechanical power and transferred to the carrier tracks and other components through a transfer
gearcase, transmission, differential, and final drives.
The engine, transmission, and steering/braking system are driver controlled. Engine startup and shutdown are controlled by
electrical signals and mechanical linkages connected to the accelerator pedal, the fuel shutoff cable, and the hand throttle
cable. Steering/braking are controlled through linkages connected to the differential.
ENGINE AND DRIVE TRAIN
The engine converts air and diesel fuel into energy. The engine delivers this power to the transmission. A drive train transfers
power from the engine to the carrier tracks. The drive train consists of the engine, transfer gearcase, transmission, differential,
drive lines, final drive assemblies, and drive sprockets.
The engine and transmission generate heat during normal operation. The cooling system transfers some of the heat to the
outside to maintain a safe operating temperature. The vent fan draws air in through the radiator, circulates it around the power
plant, and expels it through the exhaust grille above the vent fan. The vent fan is belt-driven from the engine crankshaft. A
mixture of antifreeze and water is pumped through the cooling system to cool the engine and transmission. The engine
cooling system has a capacity of 9.5 gallons (35.96 liters). The cooling system should be checked regularly. The auxiliary
radiator tank, located on the transverse beam, provides space for the separation of air and liquid coolant. Stop engine if
temperature goes above 200
C). See Cooling System illustration in Location and Description of Major Components
(WP 0002 00). Refer to Check/Fill Cooling System (M548A1) (WP 0065 00).
COLD START SYSTEM
The engine is equipped with a cold start system (air box heater). The air box heater heats the air entering the cylinders to
assist in ignition of fuel at low ambient temperatures (below 40
C). A fuel and air mixture is sprayed into the air box
and a spark ignites a flame. The flame heats the engine air, which is fed directly into the cylinders to make starting easier.
DIFFERENTIAL STEERING LEVERS
The differential steering levers are used to steer as well as stop the carrier. Pulling on one or both of the differential steering
levers applies the brakes in the differential steering unit. To turn left, gradually pull on the left steering lever. To turn right,
gradually pull on the right steering lever. To slow or stop the carrier, gradually pull both steering levers. To lock the steering
levers in place, push down on the brake lock buttons, located on top of the steering levers. To release the steering levers
brake-lock buttons, pull back on the steering levers and the buttons will pop up.
PIVOT STEER LEVERS
The pivot steer levers are used to steer the carrier while in water and to turn a stopped carrier in a tight turn. To pivot steer the
carrier, bring the carrier to a stop and pull on the pivot steer lever. Pulling the pivot lever applies the disc brake, which will
lock up the one track and allow all of the differential power to be applied to the other track.
TRANSMISSION SHIFT CONTROLLER
The transmission shifter is used to select driving range of transmission. The transmission shifter has six positions to choose
from. See drivers controls (WP 0004 00) for a description of each position. There is a neutral safety switch to make sure the
engine only starts with the transmission in neutral.