Chevrolet Silverado / GMC Sierra. Service manual — part 995

1. Attach a sling to the transmission.

2. Attach a hoist to the sling.

3. Put moderate lift tension on the hoist.

4. Disconnect and remove the transmission from the repair stand.

5. Place the transmission on the work table with the oil pan facing down.

Fig. 514: PTO Cover, Bolts & Gasket
Courtesy of GENERAL MOTORS CORP.

help when lifting the transmission. Assistance from a
hoist or another person may be required. Ensure that
lifting equipment can properly support the transmission.

2008 Chevrolet Silverado 1500

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

Silverado

6. Install the power take-off (PTO) cover gaskets (1)

7. Install 2 PTO covers (2).

8. Install 12 PTO cover bolts (3).

Tighten: Tighten the bolts to 43 N.m (31 lb ft).

DESCRIPTION & OPERATION

TRANSMISSION GENERAL INFORMATION

When attempting to diagnose a suspected 1000 Series transmission problem, always begin by
conducting the Functional Test Procedure. Refer to Functional Test. This procedure indicates
the proper path for diagnosing the transmission by making basic checks. This procedure will refer
you to the locations of specific checks. After you have determined the cause of a condition, you
either take corrective action or install a replacement transmission. Refer to Transmission
Replacement.

You must be familiar with some basic electronics in order to use this section of the manual. You
should be able to use the following special tools:

A Digital Multimeter (DMM)

A circuit tester

Jumper wires or leads

A line pressure gauge set

The functional test procedures verify the correct operation of electronic components in the
transmission. These procedures eliminate the unnecessary removal of transmission components.

NOTE:

Refer to Fastener Notice .

IMPORTANT: DO NOT, under any circumstances, attempt to diagnose a

powertrain condition without basic knowledge of this powertrain.
If you perform diagnostic procedures without this basic
knowledge, you may incorrectly diagnose the condition or
damage the powertrain components.

IMPORTANT: If you probe a wire with a sharp instrument and do not properly

seal the wire afterward, the wire corrodes and an open circuit

2008 Chevrolet Silverado 1500

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

Silverado

Diagnostic test probes are now available that allow you to probe individual wires without leaving
the wire open to the environment. These probe devices are inexpensive, easy to install and they
permanently seal the wire from corrosion.

DEFINITIONS AND ABBREVIATIONS

Throttle Position Definitions

Heavy Throttle

Approximately 75% of accelerator pedal travel

Light Throttle

Approximately 25% of accelerator pedal travel

Medium Throttle

Approximately 50% of accelerator pedal travel

Wide-Open Throttle (WOT)

Full travel of the accelerator pedal, 100% throttle

Closed Throttle

Foot is off the accelerator pedal or pedal is not depressed, 0% throttle

Throttle-Related Shift Condition Definitions

Closed Throttle Manual Downshift

A condition where the engine is used to slow the vehicle by manually downshifting during a
closed throttle coast down

Closed Throttle Coast Down

A full release of the accelerator pedal while the transmission remains in DRIVE range,
allowing the transmission to downshift as vehicle speed reduces

results.

2008 Chevrolet Silverado 1500

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

Silverado

WOT Detent Downshift

Quick apply of the accelerator pedal to its full travel, forcing a downshift

WOT Upshifts/Downshifts

Accelerator pedal is fully depressed and transmission shifts sequentially through ranges as
dictated by load and grade

Shift Condition Definitions

Bump

A sudden and forceful apply of a clutch

Delayed

A shift was expected but did not occur for several seconds, as during a manual downshift or
WOT detent downshift - may also be defined as Late or Extended

Double Bump

Two bumps felt during a clutch apply

Early

Shift occurs at lower speed than expected, often accompanied by engine laboring after an
upshift

End Bump

A firmer feel at the end of a shift than at the start of a shift

Firm

A noticeably quick apply of a clutch at medium or heavy throttle conditions - DO NOT
confuse with Harsh or Rough

Flare

A quick increase in engine speed along with a momentary loss of torque during a shift
transition - also defined as Slipping

2008 Chevrolet Silverado 1500

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

Silverado