Chevrolet Silverado / GMC Sierra. Service manual — part 742

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.

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

POSSIBLE POINTS OF FLUID LEAKS

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Transmission Oil Pan

Incorrectly tightened oil pan bolts

Improperly installed or damaged oil pan gasket

Damaged oil pan or mounting face

Incorrect oil pan gasket

Case Leak

Damaged vehicle speed sensor seal

Damaged manual shaft seal

Loose or damaged oil cooler connector fittings

Worn or damaged propeller shaft oil seal

Loose line pressure pipe plug

Porous casting warped torque converter housing

Leak at the Torque Converter End

Converter leak in the weld area

Converter seal lip cut. Check the converter hub for damage

Converter seal bushing moved forward and damaged

Converter seal garter spring missing from the seal

Porous casting of the transmission case or the oil pump

Leak at the Vent Pipe

Overfilled system

Water or coolant in the fluid; The fluid will appear milky

Transmission case porous

Incorrect fluid level indicator

Plugged vent

Drain-back holes plugged

Mispositioned oil pump to case gasket, if equipped

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado

Fig. 8: Leak Inspection Points
Courtesy of GENERAL MOTORS CORP.

Callout

Component Name

1

Automatic Transmission Electrical Connector Passage Sleeve

2

Line Pressure Test Hole Plug

3

Converter Housing to Case Joint

4

Trans Fluid Cooler Pipe Fitting Seals

5

Manual Shift Shaft Seal

6

Automatic Transmission Vent Pipe

7

Transmission Case Assembly

8

A/Trans Case Extension Seal - 2WD Models

9

Prop Shaft Front Slip Yoke Oil Seal - 2WD Models

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - 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. Make certain that the area
to be repaired is fully covered.

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

5. Repeat the fluid leak diagnosis procedures.

TRANSMISSION FLUID COOLER FLUSHING AND FLOW TEST (J 45096)

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 failure. Many repeat repair cases could have been prevented by following
published procedures for transmission oil cooler flushing and flow checking. This procedure
includes flow checking and flushing the auxiliary transmission oil cooler, if equipped.

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

10

A/Trans Fluid Pan Gasket

11

Torque Converter Fluid Seal Assembly

12

Torque Converter Assembly

13

Case Extension to Case Joint

14

Output Shaft Seal Assembly - 4WD Models

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: Use the J 45096 or equivalent to flush and flow test the

transmission oil cooler and the oil cooler pipes after the
transaxle is removed for repairs.

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Automatic Transmission - 6L50/6L80/6L90 - Cab & Chassis Sierra, Cab & Chassis Silverado,

Sierra & Silverado