Chevrolet Silverado / GMC Sierra. Service manual — part 814

switch 1 exhausts through the valve allowing the switch to close.

3-5 Reverse Boost Valve

PCS 3-5 reverse clutch fluid pressure acts on a differential area moving the 3-5 reverse clutch
boost valve against the 3-5 reverse clutch boost valve spring. The 3-5 reverse clutch fluid passes
through the valve and enters the 3-5 reverse clutch feedback circuit. As PCS 3-5 reverse clutch
fluid pressure is increased to a given value, the 3-5 reverse clutch boost valve opens the 3-5
reverse clutch feedback circuit to exhaust. This results in the 3-5 reverse clutch regulator valve
moving to the full feed position sending full 3-5 clutch reverse feed pressure (full line pressure) to
the clutch.

3-5 Reverse Clutch

The 3-5 reverse clutch fluid enters the 1-2-3-4 and reverse clutch housing to move the piston
against spring force and compensator feed fluid to apply the 3-5 reverse clutch plates.

Fig. 206: Reverse
Courtesy of GENERAL MOTORS CORP.

NEUTRAL - ENGINE RUNNING

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

When the gear selector is moved to the Neutral (N) position, the hydraulic and electrical system
operation is identical to Park (P) range. However, if Neutral is selected after the vehicle was
operating in Reverse (R), the normally high C35R pressure control solenoid 2 is commanded
OFF and the following changes would occur in the hydraulic system:

3-5 REVERSE CLUTCH RELEASES

Manual Valve

The manual valve is moved to the Neutral position and blocks line pressure from entering the
reverse and drive fluid circuits. The reverse fluid from the #2 ball check valve and clutch select
valve 3 is opened to an exhaust passage at the manual valve.

C35R Pressure Control Solenoid 2

The C35R pressure control solenoid 2 is commanded OFF allowing PCS 3-5 reverse clutch fluid
from the 3-5 reverse clutch boost valve and 3-5 reverse clutch regulator valve to exhaust.

3-5 Reverse Clutch Boost Valve

The 3-5 reverse boost valve spring force moves the valve to allow 3-5 reverse clutch feedback
fluid from the 3-5 reverse clutch regulator valve to enter the 3-5 reverse clutch circuit and
exhaust.

3-5 Reverse Clutch Regulator Valve

The 3-5 reverse clutch regulator valve spring force moves the valve to allow 3-5 reverse clutch
fluid from the 3-5 reverse clutch and clutch select valve 2 to pass through the valve and enter the
exhaust backfill fluid circuit. The 3-5 reverse clutch fluid then enters the exhaust backfill fluid
circuit and is routed through orifice #30 to the exhaust backfill pressure relief valve where excess
pressure is exhausted.

3-5 Reverse Clutch

The 3-5 reverse clutch spring force combined with a force from the compensator moves the 3-5
reverse clutch piston to release the 3-5 reverse clutch plates and force 3-5 reverse clutch fluid to
exhaust from the 1-2-3-4 and 3-5 reverse clutch housing. The 3-5 reverse clutch fluid is then
routed to the 3-5 reverse clutch regulator valve allowing the 3-5 reverse clutch to release.

Clutch Select Valve 3

When reverse fluid exhausts through the manual valve, CSV3 enable fluid moves the valve against
clutch select valve 3 spring force. The 3-5 reverse feed fluid is routed around #7 ball check valve

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

and into the 3-5 reverse supply circuit. The 3-5 reverse supply fluid is routed around #5 ball
check valve and into the 3-5 clutch reverse feed circuit and exhausts at the clutch select valve 3.

Fig. 207: Neutral - Engine Running
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE, FIRST GEAR ENGINE BRAKING

When the gear selector lever is moved to the Drive (D) range from the Neutral (N) position, the
transmission will provide engine braking. In this operating range, the normally-low C1234
pressure control solenoid 5 is commanded ON and in the engine braking mode the following
changes occur within the hydraulic circuits:

FLUID PRESSURE IS DIRECTED TO THE 1-2-3-4 CLUTCH AND THE LOW AND REVERSE
CLUTCH TO PROVIDE ENGINE BRAKING

Manual Valve

The manual valve is moved to the Drive (D) position and allows line fluid pressure to enter the
drive fluid circuit. Drive fluid is then routed to the clutch select valve 2.

Clutch Select Valve 2

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

Drive fluid at the clutch select valve 2 passes through the valve and enters the drive brake circuit.
Drive brake fluid is then routed to the clutch select valve 3.

Clutch Select Valve 3

Drive brake fluid at the clutch select valve 3 passes through the valve and enters the Drive B fluid
circuit. Drive B fluid is then routed to #1 ball check valve.

#1 Ball Check Valve

Drive B fluid seats the #1 ball check valve against drive 1-6 fluid to force drive B fluid into the
CB26/C1234 feed passage. CB26/C1234 feed fluid is routed to the #6 ball check valve, through
orifice #43 and, to the 2-6 clutch regulator valve. CB26/C1234 feed fluid passes through the 2-6
clutch regulator valve and enters the pressure switch 3 (PS3) fluid circuit. PS3 fluid is then
routed to the normally closed pressure switch 3 and opens the switch.

#6 Ball Check Valve

CB26/C1234 feed fluid seats the #6 ball check valve against the 1234 clutch feed passage forcing
CB26/C1234 feed fluid through orifice #32 before entering the 1234 clutch feed circuit. The
1234 clutch feed fluid is routed through orifice #33 and then to the 1-2-3-4 clutch regulator
valve.

1-2-3-4 CLUTCH APPLIES

C1234 Pressure Control Solenoid 5

The C1234 pressure control solenoid 5 is commanded ON allowing actuator feed limit fluid to
enter the PCS1234 clutch fluid circuit. PCS1234 clutch fluid is then routed through orifice #35 to
the 1-2-3-4 clutch regulator valve. PCS1234 clutch fluid is also routed through orifice #29 and
then to the 1-2-3-4 clutch boost valve.

1-2-3-4 Clutch Regulator Valve

PCS1234 clutch fluid moves the 1-2-3-4 clutch regulator valve against 1-2-3-4 clutch regulator
valve spring force to allow 1234 clutch feed fluid to pass through the valve and enter the 1234
clutch fluid circuit. The 1234 clutch fluid is then routed to the 1234 clutch boost valve and the 1-
2-3-4 clutch.

1-2-3-4 Clutch Boost Valve

PCS1234 clutch fluid pressure acts on a differential area moving the 1234 clutch boost valve
against the 1234 clutch boost valve spring. The 1234 clutch fluid passes through the valve and

2008 Chevrolet Silverado 1500

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

Sierra & Silverado