Chevrolet Silverado / GMC Sierra. Service manual — part 813

FLUID PRESSURE DIRECTED IN PREPARATION FOR A SHIFT

Manual Valve

Mechanically controlled by the gear selector lever, the manual valve is in the Park (P) position
and prevents line pressure from the pressure regulator valve from entering the reverse and drive
circuits.

CBR1/C456 Pressure Control (PC) Solenoid 3

The CBR1/C456 pressure control solenoid (PCS) is energized (HIGH) allowing actuator feed
limit fluid to enter the PCS CBR1/C456 CL fluid circuit. PCS CBR1/C456 CL fluid is then
routed through orifice #31 to the 4-5-6 clutch boost valve and through orifice #39 to the CBR1/
C456 clutch regulator valve.

CBR1/C456 Clutch Regulator Valve

PCS CBR1/C456 CL fluid at the CBR1/C4-5-6 clutch regulator valve moves the valve against
CBR1/C4-5-6 clutch regulator spring force and CBR1/FDBK fluid. This allows line pressure to
pass through the valve and enter the CBR1/456CL FD circuit. CBR1/456CL FD is then routed to
clutch select valve 2.

Shift Solenoid 1

Shift solenoid 1 is energized (ON) allowing actuator feed limit fluid to enter the solenoid 1
circuit. Solenoid 1 fluid is routed to the #2 ball check valve and through orifice #10 to the torque
converter clutch (TCC) regulator valve and shuttle valve (SHTL).

TCC Regulator Valve and Shuttle Valve

Solenoid 1 fluid is routed to the TCC regulator valve and shuttle valve and moves the valve
against TCC regulator valve spring force.

#2 Ball Check Valve

Solenoid 1 fluid seats the #2 ball check valve against the reverse fluid passage and fluid is forced
through orifice #22 into the CSV2 enable fluid circuit.

Clutch Select Valve 2

CSV2 enable fluid is routed to the clutch select valve 2 and moves the valve against clutch select
valve 2 spring force. This allows CBR1/456 CL FD fluid to pass through the valve and enter the
CBR1/CBR FD circuit. CBR1/CBR FD fluid is then routed: to clutch select valve 3, into the

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

CBR1 fluid circuit and, through orifice #49 where it enters the CBR fluid circuit and an exhaust
passage at the clutch select valve 3 (this fluid is intended to keep the low and reverse clutch full
of fluid but not pressurized). CBR1 fluid is then routed to the low & reverse clutch assembly in
preparation for a shift into low or reverse gear.

Shift Solenoid 2

Shift solenoid 2 is energized (ON) allowing actuator feed limit fluid to enter the solenoid 2 fluid
circuit and is then routed to the #3 ball check valve.

3-5 Reverse Clutch Regulator Valve

Actuator feed limit fluid is routed through the valve and into the PS1 fluid passage. PS1 fluid is
then sent to the normally closed #1 pressure switch and opens the switch.

#3 Ball Check Valve

Solenoid 2 fluid seats the #3 ball check valve against 456 CL fluid passage and fluid is forced
through orifice #20 into the CSV3 enable fluid circuit. CSV3 enable fluid is then routed to the
clutch select valve 3.

Clutch Select Valve #3

CSV3 enable fluid moves the clutch select valve 3 against clutch select valve 3 spring force. CBR
fluid at the clutch select valve 3 passes through the valve and exhausts.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

Fig. 205: Park - Engine Running
Courtesy of GENERAL MOTORS CORP.

REVERSE

When the gear selector lever is moved to the Reverse (R) position (from the Park position) the
normally high C35R pressure control solenoid 2 is commanded ON and the following changes
occur in the transmission's hydraulic and electrical systems:

FLUID PRESSURE DIRECTED IN PREPARATION FOR A SHIFT

Manual Valve

With the manual valve in the reverse position, line pressure is directed into the reverse fluid
circuit to the #2 ball check valve and clutch select valve 3.

#2 Ball Check Valve

Reverse fluid seats the #2 ball check valve against the solenoid 1 fluid passage and fluid is forced
through orifice #22 into the CSV2 enable circuit.

Clutch Select Valve 2

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

CSV2 enable fluid, present at the valve from Park position, continues to hold the clutch select
valve 2 against clutch select valve 2 spring force.

LOW AND REVERSE CLUTCH APPLIES

Clutch Select Valve 3

Reverse fluid from the manual valve is routed to clutch select valve 3 to combine with clutch
select valve 3 spring force to keep the valve in the off position. This allows reverse fluid to pass
through the valve and enter the 3-5 clutch reverse feed circuit. The 3-5 clutch reverse feed fluid
from the clutch select valve 3 is also routed to #5 ball check valve. CBR1/CBR FD fluid is also
directed through the clutch select valve 3 to the low and reverse clutch assembly.

Low and Reverse Clutch

CBR and CBR1 fluid pressures are routed to both the inner and outer areas of the low and reverse
clutch piston to hold the piston against spring force and hold the low and reverse clutch plates.
The clutch was already applied in Park, but is applied with more holding capacity in Reverse
(both piston areas are pressurized).

#5 Ball Check Valve

The 3-5 clutch reverse feed fluid seats #5 ball check valve against the drive 1-6 circuit allowing
3-5 clutch reverse feed fluid to enter the 3-5 reverse supply circuit. The 3-5 reverse supply fluid is
then routed to #7 ball check valve and through orifice #25 where it enters the 3-5 reverse feed
circuit. The 3-5 reverse feed passes through orifice #46 and then is routed to the 3-5 reverse
clutch regulator valve.

3-5 REVERSE CLUTCH APPLIES

C35R Pressure Control Solenoid 2

The C35R pressure control solenoid 2 is energized (HIGH) allowing actuator feed limit fluid to
enter the PCS 3-5 reverse clutch circuit. PCS 3-5 reverse clutch fluid is then routed through
orifice #48 to the 3-5 reverse clutch regulator valve and through orifice #40 to the 3-5 reverse
boost valve.

3-5 Reverse Clutch Regulator Valve

PCS 3-5 reverse clutch fluid moves the 3-5 reverse clutch regulator valve against 3-5 reverse
clutch regulator valve spring force and 3-5 reverse clutch feedback fluid. This allows 3-5 reverse
feed to pass through the valve and enter the 3-5 reverse clutch circuit. The 3-5 reverse clutch fluid
is then routed to the 3-5 reverse clutch and the 3-5 reverse boost valve. PS1 fluid from pressure

2008 Chevrolet Silverado 1500

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

Sierra & Silverado