Notes On Evaluating Brake Disks - AH42.10-D-9406-07KOP
Model 415, 420, 447, 448, 470, 471, 601, 602, 611, 636, 638, 639, 667, 668, 670, 690.6, 900, 901, 902, 903, 904, 905, 906, 907, 909, 910
Overview of possible brake disk conditions
Scoring in the friction track (C)
Score marks in the friction tracks of the brake disk (1) are permitted up to a depth of 1.5 mm.
If the score marks are deeper, the brake disk (1) must be replaced.
Crack formation across the friction track
Crack formation across the friction track
Picture F shows the crack pattern on a brake disk (1) with evaluation of the largest crack (n). The brake disk (1) shown here has reached critical limits because the crack (n) covers approx. 72% of the width of the friction track (k).
Picture G shows a through-crack to the cooling duct (arrow); the brake disk (1) is no longer permissible.
Cracks (n) with a maximum width and depth of 1.5 mm across the friction track are permissible. However, their length must not exceed 75% of the width of the friction track (k). Most cracks (n) stabilize in the center of the track at a length of 50% of the friction track width (k). If the length of the crack exceeds 75% of the friction track width (k), there is a danger that the crack (n) will penetrate through to the cooling duct.
In this case the brake disk (1) must be replaced.
Indications of thermal load on the brake disk (1)
Indications of thermal load on the brake disk (1)
- Carmine red discoloration of the cooling duct
- Crack formation
- Heat spot formation
- Pad deposits
If an increased thermal load is detected on one brake disk (1) only, then the brake caliper and brake caliper guide must be checked and then repaired or replaced according to findings. If all the brake disks (1) exhibit signs of an increased thermal load, the cause is generally because of a high vehicle load.
Heat spots on the friction track
Heat spots, dark areas on the friction track, are caused by an increased thermal load on the brake disk (1). Heat spots usually consist of a web of tiny hairline cracks, which may be the preliminary stages of crack formation. Heat spots are permitted but they may cause fluctuations in braking power and brake juddering.
The brake disk (1) must be replaced if such signs are present.
Pad deposits on the friction track
Pad deposits are caused by an increased thermal load on the brake disk (1). Pad deposits can cause major changes in the friction coefficient as well as fluctuations in braking power, brake juddering or limited brake force distribution and chatter.
The brake disk (1) must be replaced if such signs are present.
Damage and corrosion on brake disk (1)
Surface eruptions on the friction tracks, cracks (n) in the neck area or in the bolt-on flange of the brake disk (1) are not permissible. In these cases the brake disk (1) must always be replaced.
Like pad deposits, stubborn rust formation can cause changes to the friction coefficient.
In this case the brake disk (1) must be replaced.
The brake disk (1) is made of an anticorrosive cast iron alloy. If a vehicle is not driven for longer periods of time, a thin layer of rust may form on the friction tracks of the brake disk (1). This layer of rust has no effect on the working life of the brake disk (1) and is usually removed when the brakes are applied.