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 TM 55-1905-220-14-4
3-8.
MARINE GEAR- MAINTENANCE INSTRUCTION (Cont.)
(3)
Selector Valve-Forward. When a shift to the forward position is desired, the selector valve
lever is moved towards the engine. The shift causes the selector valve stem to rotate and assume the position
indicated. The 60-65 psi (414-448 kpa) oil in chamber B is directed through ports G and K to passages D and J.
Passage D is aligned with a drilled hole and channel X in the manifold. Pressurized oil from port K travels
through passage J and enters chamber L through an orifice in the orifice plate. The orifice in the plate meters
the oil for a steady, smooth pressure rise in chamber L. As chamber L fills with oil, the pressure rate control
piston moves against the springs until the piston is stopped by a shoulder in the valve body. This causes the
pressure in chamber B to rise from 60-65 psi (414-448 kpa) to an engaging pressure of 185-215 psi (1276-1482
kpa). The time required to accomplish all the above action is a very short 1-1/2 seconds. When in forward,
passage E (and channel W) remain at atmospheric pressure since slot F remains open to sump. When a shift is
made from forward to neutral, the valve stem is rotated to the position illustrated. Under these conditions,
passage D is connected to sump by slot F. Passage J also is connected to sump by port H in the valve stem.
Since passage D is connected to slot F this permits a rapid drain of oil from the forward clutch to the sump.
Since passage J is now at atmospheric pressure, the pressure in chamber L unseats the steel ball against the
compression spring permitting a rapid oil drain of chamber L to sump. When the pressure rate control piston is
against the orifice plate, the neutral position is attained again.
3-284
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