Chevrolet Silverado / GMC Sierra. Service manual — part 1179

Fig. 550: Overdrive Range, First Gear
Courtesy of GENERAL MOTORS CORP.

OVERDRIVE RANGE, SECOND GEAR

As vehicle speed increases and other operating conditions are appropriate, the PCM de-energizes
the 1-2 shift solenoid valve in order to shift the transmission to second gear.

1-2 Shift Solenoid (SS) Valve

De-energized (turned OFF) by the PCM, the normally open solenoid opens and signal A fluid
exhausts through the solenoid.

2-3 Shift Solenoid (SS) Valve

Energized (ON) as in first gear, the 2-3 shift solenoid valve blocks signal B fluid from exhausting

IMPORTANT: The actuator feed limit (AFL) fluid continues to feed the signal A

fluid circuit through orifice #25. However, the exhaust port
through the solenoid is larger than orifice #25 in order to prevent
a pressure buildup in the signal A fluid circuit. Exhausting signal
A fluid is represented by the blue arrows.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

through the solenoid. This maintains signal B fluid pressure at the solenoid end of the 2-3 shift
valve.

1-2 Shift Valve

Without signal A fluid pressure, spring force moves the valve into the upshift position. D4 fluid is
routed through the valve and fills the 2nd fluid circuit.

1-2 Shift Checkball (#8)

The 2nd fluid pressure seats the #8 checkball, flows through orifice #16, and fills the 2nd clutch
fluid circuit. This orifice helps control the 2-4 band apply rate.

2-4 Servo Assembly

The 2nd clutch fluid pressure moves the #8 checkball, flows through orifice #16 and fills the 2nd
clutch fluid circuit. This orifice helps to control the 2-4 band apply rate.

1-2 Accumulator

The 2nd clutch fluid pressure also moves the 1-2 accumulator piston against the spring force and
the accumulator fluid pressure. This action absorbs the initial 2nd clutch fluid pressure in order to
cushion the 2-4 band apply rate. Also, the movement of the 1-2 accumulator piston forces some
accumulator fluid out of the accumulator assembly. This accumulator fluid is routed back to the
accumulator valve.

Accumulator Valve

The accumulator fluid forced out of the 1-2 accumulator is orificed (#30) to the end of the
accumulator valve. This pressure moves the valve against the spring force and the torque signal
fluid pressure in order to regulate the exhaust of excess accumulator fluid. This regulation
provides additional control for the 2-4 band apply rate. The fluid circuit shows the exhaust of the
accumulator fluid during the shift by the arrow directions in the accumulator fluid circuit.

2-3 Shift Valve Train

The signal B fluid pressure from the 2-3 shift solenoid valve holds the valve train in the downshift
position. The 2nd fluid is routed through the 2-3 shuttle valve and fills the servo feed fluid circuit.

3-4 Relay Valve and 4-3 Sequence Valve

Spring force holds these valves in the downshift position (first, second and third gear positions).
The 2nd fluid is blocked by the 3-4 relay valve and the servo feed fluid is blocked by both valves

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

in preparation for a 3-4 upshift.

3-2 Downshift Valve

Spring force holds the valve closed, blocking the 2nd fluid and the 2nd clutch fluid. This valve is
used in order to help control the 3-2 downshift.

3-2 Control Solenoid Valve

In second gear, the PCM energizes the normally closed solenoid. This opens the AFL fluid circuit
to fill the 3-2 signal fluid circuit.

3-2 Control Valve

The 3-2 signal fluid pressure moves the valve against the spring force. This action does not affect
the transmission operation in second gear.

3-4 Shift Valve

Signal A fluid pressure exhausts and spring force moves the valve into the downshift position
(second and third gear positions).

Torque Converter Clutch

TCC Solenoid Valve

Under normal operating conditions, in Overdrive Range-Second Gear, the PCM keeps the
normally open TCC solenoid valve de-energized. Converter feed fluid exhausts through the open
solenoid, and spring force keeps the converter clutch apply valve in the release position.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

Fig. 551: Overdrive Range, Second Gear
Courtesy of GENERAL MOTORS CORP.

OVERDRIVE RANGE, THIRD GEAR

As vehicle speed increases further and other vehicle operating conditions are appropriate, the
PCM de-energizes the normally open 2-3 shift solenoid valve in order to shift the transmission
into Third gear.

2-3 Shift Solenoid (SS) Valve

De-energized (turned OFF) by the PCM, the solenoid opens and actuator feed limit signal B fluid
exhausts through the solenoid.

Note: AFL fluid continues to feed signal B fluid to the solenoid through orifice #29. However,
the exhaust port through the solenoid is larger than orifice #29 to prevent a buildup of pressure in
the signal B fluid circuit at the solenoid end of the 2-3 shift valve. Exhausting signal B fluid is
represented by the arrows through the solenoid.

2-3 Shift Valve Train

AFL fluid pressure at the 2-3 shift valve moves the valve train toward the solenoid. In the

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 4L60-E/4L65-E/4L70-E - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado