Chevrolet Silverado / GMC Sierra. Service manual — part 2626

Fig. 120: Inspect Gear Teeth For Severe Scoring
Courtesy of GENERAL MOTORS CORP.

11. Inspect the gear teeth for severe scoring.

Severe scoring is the same as light scoring except large areas of the tooth flank are affected.
At an advanced stage, the flank may heat up to such an extent that localized discoloring
occurs.

12. If severe scoring is present, replace the affected components.

Severe scoring is caused by the following conditions:

Inadequate oil viscosity

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Manual Transmission - Tremec 5-Speed (TZ0)

Unfavorable gear geometry

Temporary lack of lubricant

Surface roughness

Faulty heat treatment of the gears

2008 Chevrolet Silverado 1500

2008 TRANSMISSION Manual Transmission - Tremec 5-Speed (TZ0)

Fig. 121: 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 (TZ0)

Fig. 122: 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 (TZ0)