2.4.1 Park, Engine Running
When the shift lever is in park and the engine is running, the pump is turning and
therefore supplying pressure to the main pressure regulator. The main regulator
consists of the regulator valve and a boost valve. There is a pressure regulator spring
installed between the two valves.
Line pressure also passes through the manual valve and the low overrun valve and
applies the low and reverse clutch. The low and reverse clutch has no effect when the
transmission is in park.
Line pressure is also sent to the actuator fell limit (AFL) valve. The AFL valve limits the
amount of pressure in the pressure control, and shift solenoids feed circuits because the
excess pressure can damage the solenoids.
AFL oil pressure is also delivered to the shift valves and solenoids. The Electronic
Control Module (ECM) energizes both solenoids in park. AFL oil from the accumulator
limit valve cannot exit through the solenoids and pushes the shift valves to the left.
Since the solenoids are not supplied with drive oil, they cannot apply any holding
members.
The main pressure regulator also directs some oil to the torque converter clutch valve.
The torque converter clutch valve is in the released position at this time. The oil flows
through the release and apply sides of the converter clutch plate, and the converter is
unlocked.
2.4.2 Engine Running
In neutral with the engine running, the flow of oil is much like it is when the transmission
is in park. AFL oil is sent to the pressure control solenoid and continues to regulate line
pressure but has no effect on the shift valves.
In neutral, the manual valve is positioned to cut off the oil flow to the low reverse clutch
piston, and no holding members are applied in neutral.
2.4.3 Drive, First Gear
When the transmission is placed in drive with the vehicle not moving, line oil is sent to
the forward clutch piston and engages the forward clutch. This oil is called D4 oil. Under
normal conditions, the number 12 check ball seals the oil passage, forcing the D4 oil to
travel through the smaller orifice next to it. This will engage a smoother, more gentle
shift.
If the engine is at a high RPM when shifted into drive, the pressure control solenoid will
raise line pressure. This will cause the D4 oil to be higher than normal, opening the
forward abuse valve. When this valve is open, D4 oil is sent directly to the forward
clutch piston, bypassing the orifice and check ball assembly. The forward abuse valve
prevents clutch plate damage by quickly applying the clutch.
D4 oil is also directed to the accumulator valve, which fills and pressurizes the 1-2 and
3-4 accumulators. This oil is also delivered to one of the pressure switches in the
pressure switch assembly. This normally open switch closes when it is pressurized to
tell the ECM that the transmission is in drive.
2.4.4 Drive, Second Gear
When the ECM decides the transmission is to be shifted into second gear, it de-
energizes the 1-2 shift selonoid. Since this solenoid is normally open, oil exits through
NAVEDTRA 14050A
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