Chevrolet Silverado / GMC Sierra. Service manual — part 817

plates.

Fig. 212: Drive Range, Third Gear Default
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE - FOURTH 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 OFF the normally-high C35R
pressure control solenoid 2. At the same time the normally-low CBR1/C456 pressure control
solenoid 3 is commanded ON to regulate 4-5-6 clutch apply.

4-5-6 CLUTCH APPLIES

CBR1/C456 Pressure Control Solenoid 3

The CBR1/C456 pressure control solenoid 3 (PCS) is commanded ON allowing actuator feed
fluid to enter the PCS CBR1/456 clutch fluid circuit. PCS CBR1/456 clutch fluid is routed
through orifice #39 to the CBR1/C456 clutch regulator valve and, through orifice #31 to the
CBR1/C456 clutch boost valve.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

CBR1/C456 Clutch Regulator Valve

PCS CBR1/456 clutch fluid moves the CBR1/C456 clutch regulator valve against CBR1/C456
clutch regulator valve spring force to allow line fluid to pass through the valve an enter the
CBR1/456 clutch feed circuit. CBR1/456 clutch feed is then routed to the 4-5-6 clutch boost
valve and clutch select valve 2.

4-5-6 Clutch Boost Valve

PCS CBR1/456 clutch fluid pressure acts on a differential area moving the CBR1/456 clutch
boost valve against the CBR1/456 clutch boost valve spring. CBR1/456 clutch fluid passes
through the valve and enters the CBR1/456 clutch feedback circuit. As PCS CBR1/456 clutch
fluid pressure is increased to a given value, the CBR1/456 clutch boost valve opens the
CBR1/456 clutch feedback circuit to exhaust. This results in the CBR1/456 clutch regulator valve
moving to the full feed position, sending full line pressure to the clutch.

Clutch Select Valve 2

CBR1/456 clutch feed fluid passes through the clutch select valve 2 and enters the 456 clutch
feed circuit. The 456 clutch feed fluid is routed to the clutch select valve 3 where it passes
through the valve and enters the 456 clutch fluid circuit. The 456 clutch fluid is routed to the 4-5-
6 clutch, the 2-6 clutch regulator gain valve and to the #3 ball check valve. The 456 clutch fluid
seats the #3 ball check valve against solenoid 2 fluid passage and directed into the CSV3 enable
fluid circuit where it is routed through orifice #20 and to clutch select valve 3.

4-5-6 Clutch

The 456 clutch fluid enters the 4-5-6 clutch housing to move the piston against spring force,
combined with force from the compensator to apply the 4-5-6 clutch plates.

3-5 REVERSE CLUTCH RELEASES

C35R Pressure Control Solenoid 2

The C35R pressure control solenoid 2 is commanded OFF, allowing PCS 35 reverse clutch fluid
from the 3-5 reverse clutch boost valve and the 3-5 reverse clutch regulator valve to exhaust
through the solenoid.

3-5 Reverse Clutch Boost Valve

The 3-5 reverse boost valve spring force moves the valve to allow 35 reverse clutch feedback
fluid from the 3-5 reverse clutch regulator valve to enter the 35 reverse clutch fluid circuit and
exhaust.

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

3-5 Reverse Clutch Regulator Valve

The 3-5 reverse clutch regulator valve spring force moves the valve to allow 35 reverse clutch
fluid from the 3-5 reverse clutch to pass through the valve and enter the exhaust backfill fluid
circuit. The 35 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 force from the compensator move the 3-5
reverse clutch piston to release the 3-5 clutch plates and forces 35 reverse clutch fluid to exhaust
from 1- 2-3-4 and 3-5 reverse clutch housing. The 35 reverse clutch fluid is then routed to the 3-5
reverse clutch regulator valve and exhausted.

Fig. 213: Drive Range, Fourth Gear
Courtesy of GENERAL MOTORS CORP.

DRIVE RANGE, FIFTH GEAR

As the vehicle speed increases, the transmission control module (TCM) receives input signals

2008 Chevrolet Silverado 1500

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

Sierra & Silverado

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-high C35R
pressure control solenoid 2. At the same time the normally-low C1234 pressure control solenoid
5 is commanded OFF.

3-5 REVERSE CLUTCH APPLIES

C35R Pressure Control Solenoid 2

The C35R pressure control solenoid 2 is commanded ON, allowing actuator feed fluid to enter
the PCS 35 reverse clutch fluid circuit. PCS 35 reverse clutch fluid is routed through orifice #48
and then to the 3-5 reverse clutch regulator valve. PCS 35 reverse clutch fluid is also routed
through orifice #40 and then to the 3-5 reverse clutch boost valve.

3-5 Reverse Clutch Boost Valve

PCS 35 reverse clutch fluid pressure acts on a differential area moving the PCS 3-5 reverse clutch
boost valve against the 3-5 reverse clutch boost valve spring. The 35 reverse clutch fluid passes
through the valve and enters the 35 reverse clutch feedback circuit. As PCS 35 reverse clutch
fluid pressure is increased to a given value, the 3-5 reverse clutch boost valve opens the 35
reverse clutch feedback circuit to exhaust. This results in the 3-5 reverse clutch regulator valve
moving to the full feed position sending full 35 reverse clutch feed pressure (full line pressure) to
the clutch.

3-5 Reverse Clutch Regulator Valve

PCS 35 reverse clutch fluid moves the 3-5 reverse clutch regulator valve against 3-5 reverse
clutch regulator valve spring force and 35 reverse clutch feedback fluid. This allows 35 reverse
feed to pass through the valve and enter the 35 reverse clutch circuit. The 35 reverse clutch fluid
is then routed to the 3-5 reverse clutch, the 3-5 reverse boost valve and the clutch select valve 2.
When the 3-5 reverse clutch regulator valve is in this position, PS1 fluid from the pressure switch
1 exhausts through the valve allowing the switch to close.

Clutch Select Valve 2

The 35 reverse clutch fluid passes through the clutch select valve 2 and enters the 1234 clutch
default feed fluid circuit. The 1234 clutch default feed fluid is then routed to the clutch select
valve 3.

3-5 Reverse Clutch

The 35 reverse clutch fluid enters the 1-2-3-4 and 3-5 reverse clutch housing to move the piston
against spring force combined with force from the compensator to apply the 3-5 reverse clutch

2008 Chevrolet Silverado 1500

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

Sierra & Silverado