Chevrolet Silverado / GMC Sierra. Service manual — part 1184

Orificed D2 fluid pressure seats the #5 checkball against the empty overrun clutch fluid circuit.
This is done simultaneously with the overrun clutch fluid exhausting so that there is a continuous
fluid supply to the overrun clutch feed fluid circuit.

Overrun Clutch Piston

A continuous supply of fluid pressure is routed to the piston in order to keep the overrun clutch
plates applied.

Torque Converter Clutch

The converter clutch is released prior to downshifting into manual second-second gear. Under
normal operating conditions, the TCC will not apply in second gear.

Pressure Control (PC) Solenoid Valve

The PCM output signal to the PC solenoid valve increases the operating range of torque signal
fluid pressure in manual second. This provides the increased line pressure for the additional
torque requirements during the engine compression braking and increased engine loads.

IMPORTANT: Some vehicles in Manual Second Gear, at a stop, will start out in

1st gear, while others will have a second gear start. Refer to
Vehicle Owners Manual.

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

Fig. 557: Manual Second Gear
Courtesy of GENERAL MOTORS CORP.

MANUAL FIRST GEAR

A manual 2-1 downshift can be accomplished by moving the gear selector lever into the manual
first (1) position when the transmission is operating in second gear. The downshift to first gear is
controlled electronically by the PCM. The PCM will not energize the 1-2 shift solenoid valve to
initiate the downshift until the vehicle speed is below approximately 48 to 56 km/h (30 to 35
mph). Above this speed, the transmission operates in a manual first-second gear state. The
following text explains the manual 2-1 downshift.

Manual Valve

The selector lever moves the manual shaft and the manual valve into the manual first (1) position.
This allows the line pressure to enter the Lo fluid circuit.

Transmission Fluid Pressure (TFP) Manual Valve Position Switch Assembly

Lo fluid is routed to the TFP manual valve position switch where it closes the normally open lo
pressure switch. The addition of the lo pressure switch being closed signals to the PCM that
manual first is selected.

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

2-3 Shift Solenoid (SS) Valve

In both first and second gears, this solenoid is energized and maintains the signal B fluid pressure
at the solenoid end of the 2-3 shift valve train.

2-3 Shift Valve Train

Held in the downshift position by the signal B fluid pressure from the solenoid, the valve train
blocks the AFL fluid from entering the D432 fluid circuit. The D432 fluid circuit is open to
exhaust past the valve.

1-2 Shift Solenoid (SS) Valve

Below approximately 48 to 56 km/h (30 to 35 mph) the PCM energizes the normally open
solenoid. This blocks the signal A fluid pressure from exhausting through the solenoid and creates
the pressure in the signal A fluid circuit. Above this speed, the PCM keeps the solenoid de-
energized and the transmission operates in manual first-second gear.

1-2 Shift Valve

Signal A fluid pressure moves the valve against the spring force and into the downshift position.
In this position, Lo fluid from the manual valve is routed into the Lo/1st fluid circuit and D4 fluid
is blocked from entering the 2nd fluid circuit. The 2nd fluid exhausts through an orifice and an
annulus exhaust port past the valve. This orifice (#26) helps control the 2-4 band release during a
2-1 downshift.

2-4 Band Releases

2-4 Servo Assembly

The 2nd clutch fluid, which was fed by the 2nd fluid, exhausts from the servo. This allows the
spring force from the servo cushion and the servo return springs to move the 2nd apply piston and
apply the pin to release the 2-4 band. These spring forces help control the 2-4 band release.

1-2 Accumulator Assembly

The 2nd clutch fluid also exhausts from the 1-2 accumulator assembly. The spring force and the
accumulator fluid pressure move the accumulator piston to assist the 2nd clutch fluid exhaust.

Accumulator Valve

As the accumulator fluid is filling the 1-2 accumulator assembly, the accumulator valve regulates
the D4 fluid into the accumulator fluid circuit. This regulation, biased by torque signal fluid
pressure and spring force, helps control the movement of the 1-2 accumulator piston. The 2nd

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

clutch fluid exhaust, and the 2-4 band release.

1-2 Upshift Checkball (#8)

Exhausting the 2nd clutch fluid pressure unseats the ball and is routed through the 2nd fluid
circuit.

Lo and Reverse Clutch Applies

Lo Overrun Valve

The Lo/1st fluid is regulated through the lo overrun valve and into the Lo/reverse fluid circuit in
order to control the lo and reverse clutch apply.

Lo and Reverse Piston

The Lo/reverse fluid pressure acts on the inner area of the piston in order to move the piston and
in order to apply the lo and reverse clutch plates.

Overrun Clutch Applied

The overrun clutch remains applied in manual first in order to provide engine compression
braking.

Pressure Control (PC) Solenoid Valve

Similar to manual second, the PCM output signal to the PC solenoid valve increases the operating
range of the torque signal fluid pressure. This provides the increased line pressure for the
additional torque requirements during the engine compression braking and the increased engine
loads.

3-2 Downshift Control Solenoid Valve and the 3-2 Control Valve

In first gear the solenoid is OFF, the AFL fluid is blocked by the solenoid, and the 3-2 signal
fluid exhausts through the solenoid and the spring force opens the 3-2 control valve.

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado