6-39. REVERSE GEAR ASSEMBLY (Continued).
The piston type dump valve which is located at the outer diameter of the flywheel are backed up by a spring.
When the flywheel is rotated, the spring pressure tends to push the valve out toward the periphery of the flywheel. When
the control valve is opened to admit oil to operate the forward piston (5), the pressurized oil overrides the tension of the
valve spring and pushes the valve in toward the center of the flywheel. When the valve is pushed in, the valve uncovers
the port in the flywheel, leading to the piston, and admits pressurized oil into the cavity forward of the piston. The
pressurized oil moves the piston toward the drive plate, thereby locking the clutch plate between the piston and the drive
Since the drive plate (4), which is bolted to the flywheel, is in constant mesh with the sun gear (8) and the planet
carrier (18) is splined to the drive shaft, there is no relative motion between the sun gear and the planet gears (16) when
in forward drive with the result that the planet assembly including the ring gear (9) and the reverse clutch plate (10),
revolves in a forward direction with the flywheel.
When the selector control valve lever is moved to the neutral position, oil pump pressure is relieved from the
dump valve and the pressure of the spring pushes the valve out, cutting off the oil supply to the forward piston, thereby
permitting the oil to drain from the cavity forward of the piston. Thus, the piston moves forward, releasing the clutch
With the selector control valve lever set in neutral position, pump pressure is cut off from both the forward and
reverse clutch passages (A) and (C), but not from passage (B), as shown below.
Oil Flow Diagram for Lubrication of Marine Gear in Neutral Legend
Plate-Forward Clutch Drive
Shaft-Reverse Gear Drive