Chevrolet Silverado / GMC Sierra. 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