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 TM 55-1905-219-14-4
3-8. MARINE GEAR - MAINTENANCE INSTRUCTIONS (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 k pa) 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 k pa) to an engaging
pressure of 185-215 psi (1276-1482 k pa). The time required to accomplish all the above action is a very short 1-1/2
seconds. When in forward, passage E (and channed 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.
3-290
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