Twin Disc MG-5170DC, Service Manual

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Twin Disc, Incorporated
Operation
Marine Transmission Service Manual #1020667
Manual Control Valve — Neutral
Refer to Figures 7 and 8. Oil enters the control valve body through passage
A and fills chamber B. The oil causes the pressure regulating piston to partially
compress the piston outer and inner springs against the pressure-rate control
piston. This pressurizes the oil in chamber B. This pressure varies with engine
speed.
The movement of the pressure regulation piston against the springs exposes
port C in the valve body. Port C directs overage oil to the lubrication oil circuit.
Passage D (which is the engaging outlet to the primary clutch) and Passage
E (which is the engaging outlet to the secondary clutch) are interconnected by
slot F in the control valve stem when in the neutral position. The slot is aligned
with a drilled hole and cored cavity in the face of the valve body. The drilled
hole and cored cavity are aligned and drilled holes that pass through the main
housing to sump. Therefore, passages D and E are at atmospheric pressure
at this time. Also, passage J is at atmospheric pressure because port H
interconnects with slot F. This area between pistons and around springs is
vented to the sump of the transmission. This area is at atmospheric pressure
at all times permitting the return to sump of any leakage oil past the pistons.