Chevrolet Silverado / GMC Sierra. Service manual — part 2556

Fig. 141: Inspect Gears For Flank Fatigue Causing Gray Spots
Courtesy of GENERAL MOTORS CORP.

13. Inspect the gears for flank fatigue causing gray spots.

Gray spots are localized pittings on the flank caused by material fatigue or extremely fine
pittings formed on the load-bearing flanks. If they are in a cluster, they appear to the naked
eye as matte gray staining. Under high magnification, a large number of microscopic cracks
become visible on the flank. Pittings originating from these cracks may create the
appearance of local flank wear. Most of the gray spots are located in the root zone of the
gear teeth.

14. If gray spots are present, replace the affected components.

Gray spots are caused by the following conditions:

Material fatigue

Contact pressure

Sliding movement

Composite friction

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

Fig. 142: Inspect Gear Teeth For Slight Pittings
Courtesy of GENERAL MOTORS CORP.

15. Inspect the gear teeth for slight pittings.

Slight pittings or pore-like areas of individual pittings on the flank caused by material
fatigue. Usually slight pittings are only present in the root zone of the flank. Slight pittings
may cease after the run-in. A change in operating conditions may also stop continued
development of slight pitting.

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

Fig. 143: Inspect Gear Teeth For Pittings
Courtesy of GENERAL MOTORS CORP.

16. Inspect the gear teeth for pittings.

Pittings are material fatigue on the flank. The total pitting surface may become so large that
smooth running is considerably impaired or the remaining flank face, still bearing the load,

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado

will soon be destroyed by wear.

17. If pittings are present, replace the affected components.

Pitting is caused by the following conditions:

Exceeding the sliding and rolling stresses for the material

Incorrect oil viscosity

Excessive operating temperature

Fig. 144: Inspect Gears For Spalling
Courtesy of GENERAL MOTORS CORP.

2008 Chevrolet Silverado 1500

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

Silverado, Sierra & Silverado