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Chevrolet Silverado / GMC Sierra. Manual - part 1178
In the Neutral position, the manual valve blocks the line pressure from entering any other fluid
circuits. Reverse and PR fluids exhaust past the manual valve.
Lo and Reverse Clutch Releases
Lo and Reverse Clutch Piston
PR and Lo/reverse fluids exhaust from the piston, thereby releasing the lo and reverse clutch
plates. Exhausting PR fluid unseats the lo and reverse clutch checkball (#10) for a quick exhaust.
Lo Overrun Valve
Spring force closes the valve when the PR fluid pressure exhausts. Lo/reverse fluid exhausts
through the valve, into the Lo/1st fluid circuit, past the 1-2 shift valve, into the Lo fluid circuit
and through an exhaust port at the manual valve.
Reverse Input Cutch Releases
Reverse Input Clutch Piston
Reverse input fluid pressure exhausts from the piston, through the boost valve, past the #3
checkball and to the manual valve. With the reverse input fluid exhausted, the reverse input clutch
plates are released and the transmission is in Neutral.
Reverse Abuse Valve
Reverse fluid pressure exhausts and spring force closes the valve.
Boost Valve
Reverse input fluid pressure exhausts and line pressure returns to the normal operating range as in
the Park and Overdrive positions.
Reverse Input Checkball (#3)
Exhausting reverse input fluid unseats the ball for a quick exhaust through the reverse fluid circuit
and past the manual valve.
Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly
IMPORTANT: In Park, Reverse and Neutral the shift solenoid valves are shown
energized. This is the normal operating state when the vehicle is
stationary or at low vehicle speeds. However, the PCM will
change the shift solenoid valve states depending on the vehicle
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis
Silverado, Sierra & Silverado
Reverse input fluid exhausts from the TFP manual valve position switch. With no other fluid
routed to it, the TFP manual valve position switch signals the PCM that the transmission is
operating in either Park or Neutral.
Fig. 549: Neutral - Engine Running
Courtesy of GENERAL MOTORS CORP.
OVERDRIVE RANGE, FIRST GEAR
When the gear selector lever is moved to the Overdrive position, from the neutral position, the
following changes occur to the transmission's hydraulic and electrical systems:
Manual Valve
Line pressure flows through the manual valve and fills the D4 fluid circuit. All other fluid circuits
remain empty with the manual valve in the Overdrive position.
speed. For example, if Neutral is selected when the transmission
is operating in Second Gear, the shift solenoid valves will remain
in a Second Gear state. However, with the manual valve blocking
line pressure, the shift solenoid valve states do not affect
transmission operation in Park, Reverse and Neutral.
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis
Silverado, Sierra & Silverado
Forward Clutch Accumulator Checkball (#12)
D4 fluid pressure seats the checkball and is orificed (#22) into the forward clutch feed fluid
circuit. This orifice helps control the forward clutch apply rate.
Forward Clutch Accumulator Piston
Forward clutch feed fluid pressure moves the piston against spring force. This action absorbs
some of the initial increase of forward clutch feed fluid pressure to cushion the forward clutch
apply.
Forward Clutch Abuse Valve
D4 fluid pressure acts on the valve opposite of spring force. At engine speeds greater than idle,
D4 fluid pressure increases and moves the valve against spring force (as shown). D4 fluid can
then quickly fill the forward clutch feed fluid circuit, thereby bypassing the control of orifice #22
and providing a faster apply of the forward clutch. Otherwise, with increased throttle opening
and engine torque, the clutch may slip during apply.
Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly
D4 fluid pressure is routed to the TFP manual valve position switch and closes the normally open
D4 fluid pressure switch. This signals the PCM that the transmission is operating in Overdrive
range.
1-2 Shift Solenoid (SS) Valve
Energized (ON) as in Neutral, the normally open solenoid is closed and blocks signal A fluid
from exhausting through the solenoid. This maintains pressure in the signal A fluid circuit.
2-3 Shift Solenoid (SS) Valve
Energized (ON) as in Neutral, the normally open solenoid is closed and blocks signal B fluid
from exhausting through the solenoid. This maintains signal B fluid pressure at the solenoid end of
the 2-3 shift valve.
2-3 Shift Valve Train
Signal B fluid pressure at the solenoid end of the 2-3 shift valve holds the valve train in the
downshifted position against AFL fluid pressure acting on the 2-3 shift valve. In this position, the
2-3 shuttle valve blocks AFL fluid from entering the D432 fluid circuit. The D432 fluid circuit is
open to an exhaust port past the valve.
1-2 Shift Valve
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis
Silverado, Sierra & Silverado
Signal A fluid pressure holds the valve in the downshifted position against spring force. In the
First gear position, the valve blocks D4 fluid from entering the 2nd fluid circuit.
Accumulator Valve
Biased by torque signal fluid pressure, spring force and orificed accumulator fluid pressure at the
end of the valve, the accumulator valve regulates D4 fluid into accumulator fluid pressure.
Accumulator fluid is routed to both the 1-2 and 3-4 accumulator assemblies in preparation for the
1-2 and 3-4 upshifts respectively.
Rear Lube
D4 fluid is routed through an orifice cup plug (#24) in the rear of the transmission case to feed
the rear lube fluid circuit.
Pressure Control (PC) Solenoid Valve
Remember that the PC solenoid valve continually varies torque signal fluid pressure in relation to
throttle position and vehicle operating conditions. This provides a precise control of line pressure.
3-2 Control Solenoid Valve
The PCM keeps the solenoid OFF in First gear and the normally closed solenoid blocks filtered
AFL fluid from entering the 3-2 signal fluid circuit.
Torque Converter Clutch PWM Solenoid Valve
In first gear, at approximately 6 mph, the PCM operates the TCC PWM solenoid valve at
approximately a 90 percent duty cycle. This opens the AFL fluid circuit, to fill the converter
clutch signal fluid circuit through the #9 orifice, and flows to the isolator valve. The CC signal
fluid pressure, acting on the isolator valve, will move the regulated apply valve towards the
closed position. Regulated line pressure is now routed into the regulated apply circuit, and flows
to the closed converter clutch valve, and is blocked from entering the converter clutch apply
circuit. Regulated apply fluid is routed through the #8 orifice to the front of the regulated apply
valve, and regulates the line pressure entering the regulated apply circuit, in response to the CC
signal fluid acting on the isolator valve.
2008 Chevrolet Silverado 1500
2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis
Silverado, Sierra & Silverado
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