This is a typical type of gear damage. Indentations occur in the circulative face, spaced the same as the roller bodies. This kind of damage only affects the race-shaft and gear-bore-race of the selected gear. Affected areas can be identified on the roller bodies. This kind of gear damage is serious due to the very high increase in radial play on helical-cut gears. This can result in contact pattern displacement on the mating gears and can even cause tooth failure.

Fine brinelling is a combination of brinelling and wear. The race surfaces are brightly polished, but show signs of consecutive brinelling depressions.

Tribological oxidation occurs in the shaft bearing races and the gear bore races and takes the form of uniform radial wear, idler gear wear. This does not take the form of plastic deformation, but consists entirely of smoothing caused by material wear which results from fretting corrosion. The race surfaces are always highly polished, with mirror quality.

If cooling or lubrication in the needle bearings in no longer sufficient, it can lead to overheating, and cause fretting corrosion or seizure of the bearing.

Break-in-wear is not considered to be damage. Break-in-wear usually ceases after the running-in-period has expired, without damaging the components. Rough peaks produced during manufacture are worn away, or to some extent, are rolled into the surface. The surface structure, grinding and shaving marks, are still visible.

Scratches are linear indentations on the flank, running in the direction of sliding.

The marks left by the machining process are erased from the active flank. The entire flank takes on a matte gray appearance. Substantial changes take place in the tooth profile and clearance, once abrasive wear has reached an advanced stage. This not only increases the noise level, but can also cause secondary damage.

The polished tooth flanks show signs of ripple-like alterations in the surface structure, which run perpendicular to the direction of sliding, resembling a washboard.

Light scoring is the rough, partially porous lines, or areas aligned in the direction of sliding. When the film of lubricant is torn away between the flanks, this permits direct metal-to-metal contact, causing seizure or welding. These welded zones are immediately torn apart again, producing the damage associated with scoring. Scoring initially occurs in areas subjected to high hertz frequency stresses, and high sliding speeds, usually along the tooth root and tooth tip. Light scoring only covers a portion of the flank. It is not strongly developed, and has caused only insignificant wear after smoothing.

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.

Gray spots are localized pittings on the flank, caused by material fatigue, and extremely fine pittings formed on the load-bearing flanks. If they are in 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.

Slight pittings are 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 stage. A change in operating conditions may also stop continued development of slight pitting.

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, will soon be destroyed by wear.

Spalling is extensive, triangular pits on the flank, that spread 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.

Signs of overheating are the gray, blue, black discoloration of the gear, burnt oil, and reduced hardness. Due to the reduction in hardness, there is scored, or grooved flank wear in 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 and thermal deformation.

The tooth edges are worn and chipped, and in some cases, affected by plastic deformation as a result of high shift loads, ragged edges. Such severe deformation of the selector teeth edges will cause hard gear shift changes. The spline flanks may also show signs of wear resembling fretting corrosion.

Signs of corrosion are the brown, red, or black spots, sometimes with local material loss on the flank. If corrosion has not caused material loss to the flank, the sliding and rolling action of the flank can help to remove some of the corrosion.

This type of damage occurs on the roller races of the idler gears. It is characterized by what appears to be the impression of the bearing rollers. If the bearing only performs a supporting function over a long period of time, there is not movement between the gear and the supporting shaft, the bearing contact areas may show signs of fretting corrosion.