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TM 55-1905-221-14-4
6-39. REVERSE GEAR ASSEMBLY (Continued).
On the forward clutch piston type dump valves, the oil pressure behind the forward clutch piston is controlled by
the pressure sensitive centrifugally balanced dump valve moving in the cavity at the outer diameter of the flywheel.
These valves are of such weight and area that their mass exactly balances the centrifugal force of the oil pressure. A
spring behind the valve provides a constant force for returning the valve to the dump position when the oil pressure is
shut off.
Reverse rotation of the drive shaft (6) is accomplished through a planetary gear set (7). Teeth at the inner
diameter of the forward clutch drive plate (4) mesh with the teeth on the sun gear (8) which drives the planetary gear set.
A ring gear (9) surrounding the planet gears is splined to a reverse clutch plate (10) which is held stationary in reverse
between the reverse clutch drive plate (11), and the piston (12).
The reverse clutch drive plate (11) is retained by a snapring (13) assembled in the reverse gear housing and is
restrained from rotating by three dowel pins at its periphery. A reverse clutch piston (12) is mounted inside the reverse
gear housing aft of the reverse clutch plate. Like the forward drive piston, the reverse piston is mounted on drive pins
(14) to prevent radial motion.
The following figure shows the construction and illustrates the working principle of the planet assembly which
imparts a reverse motion to the drive shaft when the engine is running.


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