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 TM 55-1905-223-24-2
Section III. PRINCIPLES OF OPERATION
Overview of marine reverse reduction gearbox. The Principles of
Operation section will tell you basic information about how this
reduction gear works.
1-11. General. Power is transmitted by disk clutches and pinion gears. The direction of rotation is changed with a
counter (or intermediate) shaft arranged on the side. The reduction ratio is the same at AHEAD and ASTERN. The disk
clutches are operated by oil pressure through the control valve, and do not need to be adjusted. See FIGURE 1-2.
a. Lubrication. Operating oil pressure is built up by the gear driven pump (4), as soon as the engine is started,
and is controlled by a spring-loaded over-pressure valve. Overflow oil from this valve is used for lubrication, which
allows operation in the STOP position as long as necessary without damage. The gearbox is equipped with a
changeover-type (two-cartridge) oil filter so operation can continue if the cartridge in use becomes clogged. A fouled up
(clogged) cartridge is indicated by a red pin popping up from its normally seated position on the top of the filter head.
Changeover from one cartridge to the other is accomplished by turning the handle on the filter board. Normal oil
pressure is 260 to 280 psi, and can be adjusted if required by turning a set screw located on the oil control valve.
Operating oil is the same type as that used in the engine.
b. STOP Position. In the STOP position, the control valve diverts the oil through the non-return valve (11)
directly to the sump. The annular pistons (4) are forced to their original position by return springs (2). Clutches are
disengaged and the output shaft is stationary.
c. Counter Rotation (to Engine Rotation). The output shaft, and thus the propeller shaft, rotates in the direction
opposite to that of the drive shaft. This is the normal condition, that is, the intermediate shaft is not employed.
(1) The oil pump (14) is driven by the input shaft (10) via the spur wheels (12 and 1). The pressure oil
distributor (13) delivers the pressure oil through the bore in the drive shaft behind the piston (4).
(2) The piston (4) presses the inside and outside disks (5 and 6) together. Through the force locking of the
disks, the carrier (3) and the pinion (8) are carried along, and the power is transmitted to output shaft (7) via the wheel
(9).
d. Identical Rotation (to Engine Rotation). The oil pressure is supplied by the oil distributor (13) and the hollow
intermediate shaft (15) behind the annular piston (4). The intermediate shaft clutches are engaged and the power is
transmitted by the intermediate shaft pinion to the output gear (9). Thus, the output shaft, by engagement of the
intermediate shaft, is reversed and engine and gearbox rotate in the same direction.
e. Direction of Rotation. The direction of rotation registered on the name plate indicates the direction of input
rotation and the direction of output rotation as seen in the direction of travel. Since the two gearboxes counter rotate,
you can see that one has the intermediate shaft clutches engaged while the other has the drive shaft clutches engaged in
either drive mode.
1-5
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