Chevrolet Silverado / GMC Sierra. Service manual — part 997

2WD

Two-Wheel Drive

4WD

Four-Wheel Drive

TRANSMISSION IDENTIFICATION INFORMATION

Fig. 515: Nameplate Location
Courtesy of GENERAL MOTORS CORP.

Callout

Component Name

1

Nameplate

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

Fig. 516: Nameplate Components
Courtesy of GENERAL MOTORS CORP.

EXTERNALLY GENERATED ELECTRONIC INTERFERENCE (SPEED SENSOR SIGNALS)

Use the following procedures in order to determine if speed sensor signals, generated by a source
external to the transmission or wiring harness, are present:

1. Turn the ignition ON.

2. Keep the engine OFF.

3. If the transmission control module (TCM) is ON, install the scan tool.

Callout

Component Name

1

Date of Manufacture

2

Transmission Identification Number

3

Engineering Feature Configuration Number

4

Serial Number

IMPORTANT: If false speed signals were present at the previous shutdown,

the TCM might still be ON, even though the ignition is OFF.
The scan tool is powered by ignition power. The ignition
must be ON in order to use the scan tool to read the speed
signals.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

4. Read the speed sensor signals.

5. If a speed sensor signal is something other than one (1), there is a short to another circuit

that is carrying an AC or pulse width modulated (PWM) signal.

6. Measure the resistance of the sensor.

7. Inspect for shorts to other circuits within the harness or transmission connector.

8. Inspect to ensure there is no conductive material inside the connector.

9. Inspect to ensure the speed sensor circuit wires are a twisted pair.

10. Inspect to ensure a properly grounded drain wire.

11. Inspect for the presence of a strong external AC signal.

12. Repair or replace parts as required.

TRANSMISSION GENERAL DESCRIPTION

Allison 1000 Series transmissions are torque converter driven, fully automatic, transmission
systems. The 1000 Series transmissions have 6 forward speeds, NEUTRAL, and REVERSE. The
fifth and sixth range has overdrive gear ratio. The 1000 Series incorporates a variety of standard
and optional design features. These design features include the following:

Direct mount to engine block

Flexplate drive

Torque converter with a torque converter clutch (TCC) and integral vibration damper

3 constant-mesh planetary gear sets with helical gears

5 multiple disk clutches - 2 rotating and 3 stationary

Common hydraulic system for all transmission functions

2 transmission fluid filtration systems

Electrohydraulic control valve assembly

Electronically controlled automatic gear selection and clutch apply

Fill tube/dipstick provision on both sides of transmission

Parking pawl

Power takeoff (PTO) provision on both sides of transmission

TRANSMISSION COMPONENT AND SYSTEM DESCRIPTION

Engine/Transmission Connection

The converter housing of 1000 Series transmissions mates directly to the engine block. Flexplate

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado

drive is used for engine-to-transmission torque transfer.

Torque Converter

Several torque converters are available to match the transmissions to a wide variety of diesel and
gasoline engines. The torque converter is a single-stage, polyphase, and 3-element unit, consisting
of a pump, stator, and turbine. At lower output speeds, the torque converter multiplies torque and
provides a fluid coupling to the engine. At higher speeds, the torque converter clutch (TCC) is
automatically engaged to provide direct drive from the engine to the transmission. Hydraulic fluid
for converter charging pressure comes from the sump and is supplied by the input pump. The TCC
is applied or released by changing direction of fluid in the torque converter. An integral converter
damper minimizes the need for additional engine vibration control.

Gear Sets

The planetary gear train includes 3 constant-mesh planetary gear sets containing high-helix gears.
By the engagement of the clutches in various combinations, the planetary sets act singly or
together to provide 6 forward ranges, NEUTRAL, and REVERSE.

Clutches

5 clutches, 2 rotating and 3 stationary, direct the flow of torque through the transmission. All
range clutches are hydraulically actuated and spring-released, with automatic wear compensation.
The transmission fluid cools the clutches. The transmission control module (TCM) signals
solenoid valves to apply and release clutches based on speed and power combinations and the
range selected by the operator.

Hydraulic System

A common hydraulic system serves the torque converter and the transmission. Transmission fluid
for all hydraulic operations, lubrication, and cooling comes from the sump and is supplied by the
charging pump.

Transmission Fluid Filtration

Fluid filtration is provided by 2 filter systems. A suction filter, located in the sump, provides
general protection to the entire hydraulic system by filtering large particulates. A spin-on filter
provides full-time protection for the control solenoids and multipass protection for the entire
system. The spin-on filter is externally located on the converter housing at the lower left front of
the transmission.

Electrohydraulic Control Valve Assembly

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra &

Silverado