Chevrolet Silverado / GMC Sierra. Manual

Imbalance

Inspect the torque converter for the following conditions:

Missing or loose bolts or lugs

Missing or loose balance weights

Imbalance

FLUID LEAK DIAGNOSIS

Tools Required

J 28431-6 Fluorescent Oil Dye - 6 1 oz

J 42220 Universal 12V Leak Detection Lamp

DYE AND BLACK LIGHT METHOD

Use the J 42220 and the J 28431-6 to isolate the leak point. Fluid dye and black light kits are
also available from various tool manufacturers. All transmissions that are diagnosed, that require
replacement due to leakage, must be diagnosed with the leak dye and black light method.

1. Follow the manufacturer's instructions in order to determine the amount of dye to use.

2. Detect the leak with the black light.

3. Make the necessary repairs.

GENERAL METHOD

1. Verify that the leak is transmission fluid.

2. Thoroughly clean the suspected leak area.

3. Operate the vehicle for 24 km (15 mi), or until normal operating temperatures are reached.

4. Park the vehicle over clean paper or cardboard.

5. Shut OFF the engine.

6. Look for fluid spots on the paper.

7. Make the necessary repairs.

POWDER METHOD

1. Thoroughly clean the suspected leak area with solvent.

2. Apply an aerosol type powder, such as foot powder, to the suspected leak area.

2008 Chevrolet Silverado 1500

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

Silverado

3. Operate the vehicle for 24 km (15 mi), or until normal operating temperatures are reached.

4. Shut OFF the engine.

5. Inspect the suspected leak area.

6. Trace the leak path through the powder in order to find the source of the leak.

7. Make the necessary repairs.

FIND THE CAUSE OF THE LEAK

Pinpoint the leak and trace the leak back to the source. You must determine the cause of the leak
in order to repair the leak properly. For example, if you replace a gasket, but the sealing flange is
bent, the new gasket will not repair the leak. You must also repair the bent flange. Before you
attempt to repair a leak, check for the following conditions, and make repairs as necessary:

Gaskets

Fluid level/pressure is too high

Plugged vent or drain-back holes

Improperly tightened fasteners

Dirty or damaged threads

Warped flanges or sealing surface

Scratches, burrs, or other damage to the sealing surface

Damaged or worn gasket

Cracking or porosity of the component

Improper sealant used, where applicable

Incorrect gasket

Seals

Fluid level/pressure is too high

Plugged vent or drain-back holes

Damaged seal bore

Damaged or worn seal

Improper installation

Cracks in component

Manual or output shaft surface is scratched, nicked, or damaged

Loose or worn bearing causing excess seal wear

2008 Chevrolet Silverado 1500

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

Silverado

CASE POROSITY REPAIR

Some external leaks are caused by case porosity in non-pressurized areas. You can usually repair
these leaks with the transmission in the vehicle.

1. Thoroughly clean the area to be repaired with a cleaning solvent. Air dry the area.

2. Using instructions from the manufacturer, mix a sufficient amount of an epoxy to make the

repair.

3. While the transmission case is still hot, apply the epoxy. You can use a clean, dry soldering

acid brush to clean the area and also to apply the epoxy cement. Ensure the area to be
repaired is fully covered.

4. Allow the epoxy cement to cure for 3 hours before starting the engine.

5. Repeat the fluid leak diagnosis procedures.

TRANSMISSION FLUID COOLER FLUSHING AND FLOW TEST

GM studies indicate that plugged or restricted transmission oil coolers and pipes cause
insufficient transmission lubrication and elevated operating temperatures which can lead to
premature transmission wear-out. Many cases could have been prevented by following published
procedures for transmission oil cooler flushing and flow checking. This procedure includes
flushing and flow checking the auxiliary transmission oil cooler, if equipped. GM requires that
transmission oil cooler flushing and flow checking be performed whenever a transmission is
removed from the vehicle for service within warranty, including:

Goodwrench SRTA

Major overhaul

Torque converter replacement

Oil pump replacement

CAUTION: Epoxy adhesive may cause skin irritations and eye

damage. Read and follow all information on the container
label as provided by the manufacturer.

IMPORTANT: The J 45096 - Automatic Transmission Oil Cooler Flush and Flow

Test Tool can be used to flush the transmission oil cooler system
on an Allison equipped vehicle, but the flow meter should not be
utilized.

2008 Chevrolet Silverado 1500

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

Silverado

Only GM Goodwrench DEXRON® VI automatic transmission fluid should be used when doing
warranty repair on GM transmissions.

Tools Required

J 35944-A Transmission Oil Cooler and Line Flusher

J 35944-22 Transmission Oil Cooler Flushing Fluid

J-44835-1 Transmission Oil Cooler Flusher Adapters

Measuring cup

Funnel

Water supply - hot water recommended

Water hose at least 16 mm (5/8 in) ID

Shop air supply - with water/oil filters, regulator and pressure gage

Air chuck with clip, if available

Oil drain container

Minimum 19 L (5 gallon) pail or similar container with lid

Eye protection

Rubber gloves

PREPARATION

1. After the repair or replacement transmission is installed in the vehicle, do not connect the oil

cooler pipes again.

2008 Chevrolet Silverado 1500

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

Silverado

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Chevrolet Silverado / GMC Sierra. Manual - part 835