Chevrolet Silverado / GMC Sierra. Service manual — part 815

enters the 1234 clutch feedback circuit. As PCS 1234 clutch fluid pressure is increased to a given
value, the 1234 clutch boost valve opens the 1234 clutch feedback circuit to exhaust. This results
in the 1234 clutch regulator valve moving to the full feed position sending full 26 CL/1234 CL
feed pressure (full line pressure) to the clutch.

1-2-3-4 Clutch

The 1234 clutch fluid enters the 1234 clutch housing to move the piston against spring force and
compensator feed fluid to apply the 1-2-3-4 clutch plates.

Fig. 208: Drive Range, First Gear Engine Braking
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE, FIRST GEAR

As the vehicle speed increases, the transmission control module (TCM) receives input signals
from the automatic transmission input and output speed sensors, throttle position sensor and other
vehicle sensors to determine the precise moment to deenergize or "turn off" shift solenoid 1 and
command OFF the normally-high CBR1/C456 pressure control solenoid 3.

LOW & REVERSE CLUTCH RELEASES

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Shift Solenoid 1

When shift solenoid 1 is "turned OFF", CSV2 enable fluid from the clutch select valve 2 passes
by the #2 ball check valve and enters the solenoid 1 fluid circuit. Solenoid 1 fluid from the #2
ball check valve and TCC regulator valve is then routed to the solenoid where it exhausts.

Clutch Select Valve 2

Clutch select valve 2 (CSV2) enable fluid is exhausted from the clutch select valve 2 and clutch
select valve 2 spring force moves the valve to the released position. With clutch select valve 2 in
the released position, drive fluid from the manual valve passes through the valve and enters the
drive 1-6 fluid circuit. Drive 1-6 fluid then feeds all clutch regulator valves and the TCC
regulator valve.

CBR1/C456 Pressure Control Solenoid 3

The CBR1/C456 pressure control solenoid 3 is commanded OFF allowing PCS CBR1/C456
fluid from the CBR1/C456 clutch regulator valve and 456 clutch boost valve to exhaust.

CBR1/C456 Clutch Regulator Valve

CBR1/C456 clutch regulator valve spring force moves the valve to exhaust the CBR1/456 clutch
feed circuit and allow drive 1-6 fluid to enter the PS5 fluid circuit. PS5 fluid is then routed to the
normally-closed pressure switch 5 and opens the switch. PS5 fluid is also routed to the #4 ball
check valve and flows into the CSV2 latch fluid circuit.

#4 Ball Check Valve

PS5 fluid pressure seats the #4 ball check valve against the 456 clutch fluid circuit. PS5 fluid is
then directed into the CSV2 latch fluid circuit and routed to the clutch select valve 2. CSV2 latch
fluid combines with clutch select valve 2 spring force and holds the valve in this position during
all 6 forward gear ranges.

#5 Ball Check Valve

Drive 1-6 fluid pressure seats the #5 ball check valve against the 35 clutch reverse feed fluid
passage. Drive 1-6 fluid is then directed into the 35R supply fluid circuit which is routed to the
#7 ball check valve and orifice #25.

#7 Ball Check Valve

The 35R supply fluid seats the #7 ball check valve against the 35R feed fluid passage to force
35R supply fluid through orifice #25 before entering the 35R feed circuit. The 35R feed fluid is

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

then routed to the 3-5 reverse clutch regulator valve.

Low and Reverse Clutch

Low and reverse clutch spring force moves the low and reverse clutch piston which forces clutch
braking (CBR) and CBR1 fluid out of the center support. CBR fluid is routed to the clutch select
valve 3 where it exhausts. CBR1 fluid is routed to the clutch select valve 2 where it exhausts. The
low and reverse clutch is in the released position.

Fig. 209: Drive Range, First Gear
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE, SECOND GEAR

As the vehicle speed increases, the transmission control module (TCM) receives input signals
from the automatic transmission input and output speed sensors, the throttle position sensor and
other vehicle sensors to determine the precise moment to command ON the normally-low pressure
control solenoid 4.

SECOND CLUTCH APPLIES

CB26 Pressure Control Solenoid 4

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

The CB26 pressure control solenoid 4 is commanded ON, allowing actuator feed limit fluid to
enter the pressure control solenoid (PCS) 26 clutch fluid circuit. PCS 26 clutch fluid is then
routed through orifice #44 to the 2-6 clutch regulator gain valve.

2-6 Clutch Regulator Gain Valve

The 2-6 clutch regulator gain valve allows the gain (valve input to output pressure magnification
factor) of the 2-6 clutch regulator valve to be different for a 1-2 shift verses a 5-6 shift. For a 1-2
shift, PCS 26 clutch fluid pressure acts on a differential area resulting in the "high gain" pressure
output.

2-6 Clutch Regulator Valve

PCS 26 clutch fluid moves the 2-6 clutch regulator / gain valve assembly against the 2-6 clutch
regulator valve spring force to allow 26 clutch/1234 clutch feed fluid to pass through the valve.
The 26 clutch/1234 clutch feed fluid is routed into the 26 clutch fluid circuit where it passes
through orifice #41 and then to the spring end of the 2-6 clutch regulator valve, and to the 2-6
clutch within the center support.

2-6 Clutch

The 26 clutch fluid from the 2-6 clutch regulator valve is routed through the center support and to
the 2-6 clutch piston assembly. The 26 clutch fluid pressure moves the piston against 2-6 clutch
spring force to apply the 2-6 clutch plates.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado