General Information On PCCP Brake Discs
The brake discs have wear indicator plates in the friction surfaces. The wear indicator plates (six on each brake disc) are arranged at three points close to the outer diameter, offset by 120° -arrows- . The three wear indicator plates on each friction surface (three on the inside and three on the outside) are positioned directly opposite each other. Each wear indicator is approx. 1.2 cm2 . The wear indicators are barely visible on new brake discs.
The minimum brake disc thickness (wear dimension) is stamped on the brake disc hub (example: Min. Th. 33.7 mm).
Wear indicators
When replacing brake discs as a result of wear, both brake discs on an axle must be replaced!
Irrespective of wear, a brake disc may have to be replaced if there is edge damage on the brake disc friction surfaces! In this case, only one brake disc can be replaced if the friction surface of the other PCCB brake disc is still as-new.
Cracks in the brake disc friction surface:
Due to the composition of different materials in the friction layer and support body, the friction surfaces (even when new) are coated with an uncritical crack pattern (stress-relief microstructure). Individual relaxation cracks sometimes run along the perforated bores. > Stress-relief microstructure in PCCB brake disc friction surfaces
The stress-relief microstructure results from the way in which the brake disc surface is manufactured and is not a safety risk . There is also no danger of the friction layers flaking off from the support body, since the friction layers are almost free of internal stresses as a result of the stress-relief microstructure.
The stress-relief microstructure is sometimes clearly visible in new brake discs and the brake disc hub side and the side that is opposite to the hub can differ significantly from one another.
Cracks in the brake disc friction surfaces must therefore be viewed differently to cracks in grey cast-iron brake discs. These cracks are not regarded as wear criteria for PCCB brake discs and may even be present on new brake discs, depending on the manufacturer.
Stress-relief microstructure in PCCB brake disc friction surfaces