Break-in-wear is not considered to be damage because it 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.

Scratches can be caused by the following conditions:

The marks left by the machining process are erased from the active flank. Instead, 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 cause secondary damage.

Abrasive wear is caused by the following conditions:

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.

Rippling or brinelling is caused by the following conditions:

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 part of the entire surface of the flank, or is not strongly developed and has caused only insignificant wear after smoothing.

Light scoring is caused by the following conditions:

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.

Severe scoring is caused by the following conditions:

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.

Gray spots are caused by the following conditions:

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.

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.

Pitting is caused by the following conditions:

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.

Spalling is caused by the following conditions:

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 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.

Overheating is caused by the following conditions:

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.

Gear change damage is caused by the following conditions:

Corrosion may appear as brownish red to 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.

Corrosion is caused by the following conditions:

This type of damage occurs on the roller races of the idler gear. This type of damage 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, and the bearing contact areas may show signs of fretting corrosion.