Hummer H2. Manual — part 2596

Fig. 330: Overdrive Range, 4-3 Downshift
Courtesy of GENERAL MOTORS CORP.

2004 Hummer H2

2004 TRANSMISSION/TRANSAXLE Automatic Transmission - Overhaul - 4L60-E/4L65-E

OVERDRIVE RANGE, 3-2 DOWNSHIFT

Similar to a forced 4-3 downshift, a forced 3-2 downshift can occur because of minimum throttle (coastdown
conditions), heavy throttle or increased engine load. In order to achieve a forced 3-2 downshift, the PCM
energizes the 2-3 shift solenoid valve and the following changes occur:

Energized by the PCM, the normally open solenoid closes and blocks the signal B fluid from exhausting
through the solenoid. This creates pressure in the signal B fluid circuit at the solenoid end of the 2-3 shift valve.

2-3 Shift Valve Train

The signal B fluid pressure from the shift solenoid moves both valves to the downshift position against AFL
fluid pressure acting on the 2-3 shift valve. This causes the following changes:

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The AFL fluid is blocked from the D432 fluid circuit and the D432 fluid exhausts past the 2-3 shuttle
valve.

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The 2nd fluid is blocked from feeding the 3-4 signal fluid circuit and the 2nd fluid is routed into the servo
feed fluid circuit.

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The 3-4 signal fluid is exhausted past the valve. The 3-4 clutch fluid and the 3rd accumulator fluid, which
were fed by the 3-4 signal fluid, also exhaust.

3-4 Clutch Releases and 2-4 Band Applies

3-4 Clutch Piston

The 3-4 clutch fluid exhausts from the piston and the 3-4 clutch plates are released.

3-4 Clutch Exhaust Checkball (#4)

Exhausting 3-4 clutch fluid seats the #4 checkball and is forced through orifice #13. This orifice controls the 3-4
clutch fluid exhaust and the 3-4 clutch release rate.

2-4 Servo Assembly

The 3rd accumulator fluid exhausts from the servo assembly. The 2nd clutch fluid pressure moves the 2nd
apply piston against the servo return spring force in order to move the apply pin and apply the 2-4 band.

3-2 Downshift Valve and 1-2 Upshift Checkball (#8)

The 3-4 clutch fluid exhausts from the valve and the spring force moves the valve into the second gear position.
However, before the spring force overcomes the exhausting 3-4 clutch fluid pressure, the 2nd fluid feeds the
2nd clutch fluid circuit through the valve. This bypasses the control of orifice #16 at the #8 checkball and
provides a faster 2-4 band apply. Remember that the #8 checkball and orifice #16 are used to help control the 2-
4 band apply during a 1-2 upshift.

Downshift Timing and Control

2004 Hummer H2

2004 TRANSMISSION/TRANSAXLE Automatic Transmission - Overhaul - 4L60-E/4L65-E

At higher vehicle speeds, the 2-4 band apply must be delayed to allow the engine speed RPM to increase
sufficiently for a smooth transfer of engine load to the 2-4 band. Therefore, exhaust of the 3rd accumulator fluid
must be delayed. However, at lower speeds the band must be applied quickly. In order to provide for the
varying requirements for the 2-4 band apply rate, the exhausting 3rd accumulator fluid is routed to both the 3rd
accumulator checkball (#2) and the 3-2 control valve.

3rd Accumulator Checkball (#2)

The exhausting 3rd accumulator fluid seats the #2 checkball and is forced through orifice #12. This fluid
exhausts through the 3-4 clutch and the 3-4 signal fluid circuits and past the 2-3 shift valve. Orifice #12 slows
the exhaust of the 3rd accumulator fluid and delays the 2-4 band apply rate.

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

These components are used to increase the exhaust rate of 3rd accumulator fluid, as needed, depending on the
vehicle speed.

The 3-2 control solenoid valve is a normally closed On/Off solenoid controlled by the PCM. The PCM controls
the solenoid state during a 3-2 downshift according to vehicle speed.

Low Speed

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At lower vehicle speeds, the PCM operates the 3-2 control solenoid valve in the Off position.

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In the Off position the solenoid blocks actuator feed limit fluid pressure from the 3-2 control valve.

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With no actuator feed limit fluid pressure, the 3-2 control valve spring force keeps the valve open to
allow a faster exhaust of 3rd accumulator fluid through orifice #14 into the 3-4 clutch fluid circuit.

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A faster exhaust of the 3rd accumulator exhaust fluid provides a faster apply of the 2-4 band, as needed at
lower vehicle speeds.

High Speed

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At high vehicle speed, the PCM operates the 3-2 control solenoid valve in the On position allowing
actuator feed limit fluid to pass through the solenoid. This pushes the 3-2 control valve into the closed
position.

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This action permits a slow apply of the 2-4 band by blocking off 3rd accumulator exhaust fluid from
entering the 3-4 clutch fluid circuit through orifice #14.

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This allows the engine speed to easily come up to the necessary RPM before the 2-4 band is applied.

3rd Accumulator Exhaust Checkball (#7)

After the downshift is completed, the #7 checkball unseats and allows the residual fluid in the 3rd accumulator
fluid circuit to exhaust.

Pressure Control (PC) Solenoid Valve

Remember that the PC solenoid valve continually adjusts torque signal fluid in relation to the various PCM

2004 Hummer H2

2004 TRANSMISSION/TRANSAXLE Automatic Transmission - Overhaul - 4L60-E/4L65-E

input signals (mainly the throttle position).

2004 Hummer H2

2004 TRANSMISSION/TRANSAXLE Automatic Transmission - Overhaul - 4L60-E/4L65-E