Chevrolet Silverado / GMC Sierra. Service manual — part 2557

18. Inspect the gears for spalling.

Spalling is extensive triangular pits on the flank, spreading from a zone of gray spots or a
fine line of pits at the root. The depth of the exposed surface is relatively constant
throughout. Further cracks may extend from the pits at an angle. In some cases, the damage
may even progress into the tip zone, causing tip damage.

19. If spalling is present, replace the affected components.

Spalling is caused by the following conditions:

Exceeding the sliding and rolling stresses for the material

Incorrect oil viscosity

Excessive operating temperature

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Manual Transmission - Tremec 5-Speed (M96) - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

Fig. 145: Inspect Gears For Overheating
Courtesy of GENERAL MOTORS CORP.

20. Inspect the gears for overheating.

Grayish to bluish black discoloration of the gear, burnt oil, and reduced hardness is caused
by overheating. Due to the reduction in hardness, there is scored or grooved flank wear in

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Manual Transmission - Tremec 5-Speed (M96) - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

the direction of sliding, particularly in the tip and root zones. If there is extreme
overheating, the material softens, causing distortion of the gear teeth such as, bent teeth -
thermal deformation.

21. If damage from overheating is present, replace or repair the affected components.

Overheating is caused by the following conditions:

Temporary or complete lack of lubrication - low oil level

Very high peripheral speeds

Insufficient tooth clearance

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Manual Transmission - Tremec 5-Speed (M96) - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado

Fig. 146: Inspect Selector Teeth Of Gears For Gear Change Damage
Courtesy of GENERAL MOTORS CORP.

22. Inspect the selector teeth of the gears for gear change damage.

The tooth edges are worn and chipped and, in some cases, affected by plastic deformation as

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Manual Transmission - Tremec 5-Speed (M96) - Cab & Chassis Sierra, Cab & Chassis

Silverado, Sierra & Silverado