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 TM 55-1905-219-14-4
3-8. MARINE GEAR - MAINTENANCE INSTRUCTIONS (Cont).
(4) Selector Valve-Reverse. When a shift to the reverse position is desired, the selector valve lever is moved away
from 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 E and J. Passage E is aligned with a drilled
hole and channel W in the manifold. Pressurized oil from port G 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 engageing 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 reverse, passage D (and channel X) remains at atmospheric pressure since slot F remains open to sump. When
a shift is made from reverse to neutral, the valve stem is rotated to the position illustrated. Under these conditions,
passage E is connected to sump by slot F. Passage J also is connected to sump by port H in the valve stem. Since
passage E is connected to slot F, this permits a rapid drain of oil from the reverse 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.
3-292
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