Chevrolet Silverado / GMC Sierra. Service manual — part 1180

upshifted position, the following changes occur:

AFL fluid is routed through the 2-3 shift valve and fills the D432 fluid circuit.

2nd fluid is blocked from entering the servo feed fluid circuit and is orificed (#28) into the
3-4 signal fluid circuit. This orifice helps control the 3-4 clutch apply rate.

Servo feed fluid exhausts past the valve into the 3-4 accumulator fluid circuit and through an
exhaust port at the 3-4 relay valve.

3-4 Clutch Exhaust Checkball (#4)

3-4 signal fluid unseats the ball and enters the 3-4 clutch fluid circuit.

3-4 Clutch Piston

3-4 clutch fluid pressure moves the piston to apply the 3-4 clutch plates and obtain 3rd gear.
However, the 2-4 band must release as the 3-4 clutch applies.

3rd Accumulator Checkball (#2)

3-4 clutch fluid pressure unseats the ball and fills the 3rd accumulator fluid circuit.

3rd Accumulator Exhaust Checkball (#7)

3rd accumulator fluid seats the ball against the orificed exhaust and is routed to the released side
of the 2nd apply piston. Before the #7 checkball seats, air in the 3rd accumulator fluid circuit is
exhausted through the orifice.

2-4 Servo Assembly

3rd accumulator fluid pressure acts on the release side of the 2nd apply piston and assists servo
return spring force. The surface area on the release side of the piston is greater than the surface
area on the apply side. Therefore, 3rd accumulator fluid pressure and servo return spring force
move the 2nd apply piston against 2nd clutch fluid pressure. This action serves two functions:

Move the apply pin to release the 2-4 band.

Act as an accumulator by absorbing initial 3-4 clutch fluid to cushion the 3-4 clutch apply
rate. Remember that the 3rd accumulator fluid circuit is fed by 3-4 clutch fluid.

3-2 Downshift Valve

3-4 clutch fluid pressure moves the valve against spring force. This opens the valve and allows
2nd fluid to feed the 2nd clutch fluid circuit through the valve.

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

3-2 Control Solenoid Valve and 3-2 Control Valve

The solenoid remains open and routes AFL fluid into the 3-2 signal fluid circuit. 3-2 signal fluid
pressure holds the 3-2 control valve against spring force, thereby blocking the 3rd accumulator
and 3-4 clutch fluid circuits.

1-2 Shift Solenoid (SS) Valve and 1-2 Shift Valve

The 1-2 SS valve remains de-energized and signal A fluid is exhausted through the solenoid. Also,
D432 fluid pressure from the 2-3 shift valve assists spring force to hold the 1-2 shift valve in the
upshifted position.

3-4 Shift Valve

Spring force holds the valve in the downshifted position, blocking 3-4 clutch fluid in preparation
for a 3-4 upshift.

Torque Converter Clutch

TCC Solenoid Valve

Under normal operating conditions, in Overdrive Range-Third 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. However, at
speeds above approximately 121 km/h (75 mph), with the transmission still in third gear, the
PCM will command TCC apply in third gear. Refer to Overdrive Range, Fourth Gear -
Torque Converter Clutch Applied for more information on TCC apply.

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

Fig. 552: Overdrive Range, Third Gear
Courtesy of GENERAL MOTORS CORP.

OVERDRIVE RANGE, FOURTH GEAR - TORQUE CONVERTER CLUTCH APPLIED

At higher vehicle speeds, the Hydra-matic 4L60-E transmission uses an overdrive gear ratio
(fourth gear) in order to increase fuel economy and in order to maximize engine performance.
When vehicle operating conditions are appropriate, the PCM energizes the 1-2 shift solenoid
valve to shift the transmission into fourth gear.

1-2 Shift Solenoid (SS) Valve

Energized (turned ON) by the PCM, the normally open solenoid closes and blocks signal A fluid
from exhausting through the solenoid. This creates pressure in the signal A fluid circuit.

2-3 Shift Solenoid (SS) Valve

De-energized (OFF) as in third gear, the 2-3 shift solenoid valve exhausts signal B fluid through
the solenoid.

1-2 Shift Valve

D432 fluid pressure from the 2-3 shift valve and spring force hold the valve in the upshift position

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

against signal A fluid pressure.

3-4 Shift Valve

Signal A fluid pressure moves the valve into the upshift position against the spring force. In this
position, the valve routes 3-4 signal fluid into the 4th signal fluid circuit.

3-4 Relay Valve and 4-3 Sequence Valve

4th signal fluid pressure moves both valves into the upshift (fourth gear) position against the
spring force acting on the 4-3 sequence valve. This causes the following changes:

Orificed (#7) 2nd fluid is routed through the 3-4 relay valve and into the servo feed fluid
circuit.

Servo feed fluid is routed through the 4-3 sequence valve and into the 4th fluid circuit.

3-4 accumulator fluid routed from the 2-3 shuttle valve is blocked by both valves.

2-4 Servo Assembly

4th fluid is routed through the center of the servo apply pin and acts on the apply side of the 4th
apply piston. 4th fluid pressure moves the 4th apply piston against the apply pin spring force
acting on the release side of the 4th apply piston. This action moves the apply pin and applies the
2-4 band in order to obtain fourth gear.

2-4 Band Apply Accumulation

2-3 Shift Valve Train

The valve train remains in the upshift position with the AFL fluid pressure acting on the 2-3 shift
valve. In addition to its operation third gear, the 2-3 shift valve directs servo feed fluid into the 3-
4 accumulator fluid circuit.

3-4 Accumulator Assembly

3-4 accumulator fluid pressure moves the 3-4 accumulator piston against spring force and orificed
accumulator fluid pressure. This action absorbs initial 4th clutch apply fluid pressure in order to
cushion the 2-4 band apply. Remember that both of the 3-4 accumulator and 4th fluid circuits are
fed by servo feed fluid. As 3-4 accumulator fluid fills the accumulator, any air in the system will
exhaust through office #19. This piston movement forces some orificed accumulator fluid out of
the 3-4 accumulator assembly.

3-4 Accumulator Checkball (#1)

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado