TRUCK SERVICE MANUAL
TRANSMISSION
DESCRIPTION AND OPERATION
Para 2-23/2-26
(2) The oil filter screens all oil entering the
(3) F or models equipped with a hydraulic
hydraulic system.
retarder, the oil is discharged from two sections of the
input pump. The first section directs oil (red) to the
main-pressure regulator valve (item (2), above). The
2-25. REAR COVER (A, foldout 16)
second section directs oil (black and green) to the
lubrication circuit, and assists in providing oil to the
Rear cover 14 is made of cast iron and machined to
converter-in circuit.
receive governor assembly 38 and first or low clutch
piston 4. The rear cover provides support for output
d. Main-Pressure Circuit
shaft assemblies 19.
A parking brake mounting face
(foldouts 5, )
is also provided on the rear surface. The cover is the
rear closure member and is attached to
the adapter
(1) Main pressure (red) is regulate by the
housing by twenty-four bolts 17 and 36.
main-pressure regulator valve. Oil from the pump flows
into the valve bore, through an internal passage in the
2-26. HYDRAULIC SYSTEM
valve, to the upper end of the valve. Pressure at the
The hydraulic system
a. System Functions.
upper end of the valve forces the valve downward
generates, directs, and controls the pressure and flow of
against the spring until oil (yellow) flows into the
the hydraulic fluid within the transmission. The hydraulic
converter-in circuit. When flow from the pump exceeds
fluid (transmission oil) is the power transmitting medium
the circuit requirement, the converter bypass valve opens
in the torque converter. Its velocity drives the converter
and allows the excess to escape into the converter-out
turbine. Its flow cools and lubricates the transmission
circuit (orange).
and its pressure applies the clutches.
(2) Although main pressure is controlled
b. System Schematics.
A Color-coded foldout
primarily by the spring force below the regulator valve, it
illustration of the hydraulic system IS presented at the
is also affected by the presence of forward regulator
back of this manual (foldouts
5, ). Each illustration
pressure. When this pressure is not present at the
represents the system as it would function during neutral
regulator valve, main pressure is regulated at a higher
operation and with the engine idling.
value.
c. Oil Filter, Pump Circuit
(3) Main pressure (red) is directed to several
(foldouts 5, )
points in the hydraulic circuit.
(1) Oil (blue) is drawn from the sump
e. Converter, Cooler, Lubrication
(transmission oil pan) through a fine-mesh filter screen
Circuit (foldouts 5, )
by the input-driven pump assembly.
(1) The converter circuit originates at the
(2) The oil (red) is discharged by the input
main-pressure regulator valve. Converter-in oil (yellow)
pump through an external filter (when so equipped) and
flows to the torque converter. Oil must flow through the
into the bore of the main pressure regulator valve.
converter continuously to keep it filled and to carry off the
heat generated within the converter.
(2) Converter-out oil (orange) leaving the
torque converter, is directed to an external cooler
(supplied by vehicle or engine manufacturer). When the
transmission includes a hydraulic retarder, converter-out
oil flows through the retarder control valve
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