The axle propel pump is mounted to the rear of the engine.
The charge pressure for the propel system is supplied by the
steering pump. When the engine is running, drive shaft (1) and
barrel assembly (10) are rotating. There are nine pistons (13)
in the barrel assembly. Port plate (5) and swashplate (14) are
fastened to case (9). The port plate and the swashplate do not
rotate. Spring washers (12) keep a force on the barrel
assembly in order to make a high pressure seal between the
barrel assembly and the pod plate. When the barrel assembly
is rotating, each piston (13) follows the angle of the
swashplate. If the swashplate angle is at zero, the pistons do
not move in and out of the barrel assembly and there is no oil
The position of the swashplate is controlled by the manual
directional control valve (4) and servo valve (3). Movement of
the propel control lever moves the directional control valve.
The directional control valve routes charge oil into the servo
valve. The servo valve controls the direction and the amount
of the swashplate angle.
The steering pump maintains charge oil in the propel pump in
order to keep the barrel assembly full of oil. The charge oil
lubricates the pump components. The internal loss of oil due
to leakage is replenished by the charge oil. The charge oil is
also used in order to release the brakes and the charge oil will
provide the shift valve with oil.
Oil flows from the axle propel pump to the axle propel motor
and back to the axle propel pump by way of inlet/outlet ports
(6) and (8). The position of the swashplate determines the
direction of flow as well as the high pressure side of the two