34 00... Consult The Boundary Samples Catalogue When Assessing The Appearance Of Carbon Ceramic Brake Discs

Structure of a carbon ceramic brake disc:

1. Ceramic friction layer.
2. Carbon base.
3. Coolant duct.

To ensure that the ceramic brake disc has a long service life, the base is provided with a separate friction layer. The friction layer is bonded by means of a special joining paste. The siliconization results in a bonded connection.

The base and the friction layer are made from different mixtures/recipes. For this reason, the two components differ in appearance.

Fig 1: Carbon Ceramic Brake Disc Structure

Courtesy of BMW OF NORTH AMERICA, INC.

Tension relief structure: 

Due to the different material compositions of the friction layer and base, the friction surfaces (even when new) are characterized by a harmless tension relief structure. Some relief cracks pass along the perforation bore holes.

The tension relief structure arises during the manufacturing process, starting from the brake disc surface, and is not a safety risk. There is also no danger that the friction layers may split off the base in large pieces since because the friction layers are virtually tension free due to the tension relief structure.

The tension relief structure is partially visible on new components and may vary considerably between the two brake disc chamber sides.

Thus, a brake disc with this feature is OK.

Fig 2: Brake Disc Tension Relief Structure

Courtesy of BMW OF NORTH AMERICA, INC.

Rough surfaces in coolant duct: 

The surfaces (1) in the coolant duct have a different structure. The coolant ducts are not finished and therefore have a rough structure.

Thus, a brake disc with this feature is OK.

Fig 3: Rough Surfaces In Coolant Duct

Courtesy of BMW OF NORTH AMERICA, INC.

Processing traces: 

The surface of the ceramic brake disc is characteristic of the type of grinding applied. The cross and spiral pattern (see arrows) created by the type of grinding process has no influence on the performance of the component.

Thus, a brake disc with this feature is OK.

Fig 4: Locating Surface Of Ceramic Brake Disc

Courtesy of BMW OF NORTH AMERICA, INC.

Pores in base: 

Due to the carbon fibres used, with a defined length of 10 mm without a short fibre portion, visible pores arise in the base during the manufacturing process. These pores have no negative influence on the function of the ceramic brake disc.

e.g.:

1. Pores on brake disc chamber screw connection.
2. Pores on the brake disc face.
   Fig 5: Pores On Brake Disc Chamber Screw Connection And Brake Disc Face

   Courtesy of BMW OF NORTH AMERICA, INC.

Possible surface flaws on the brake disc: 

Flaws on perforation bore holes  .

1. Brake disc OK.
2. Brake disc not OK -> nest-shaped pittings.
   Fig 6: Flaws On Perforation Bore Holes

   Courtesy of BMW OF NORTH AMERICA, INC.

Brake disc not OK.

-> Nest-shaped pittings (3 or more holes on each side).

Fig 7: Perforation Bore Holes Wrong Shapes

Courtesy of BMW OF NORTH AMERICA, INC.

Flaws in friction layer: 

Pittings in friction layer: 

Image (A). Brake disc OK.

Image (B): Brake disc not OK.

Fig 8: Pittings And Flaws In Friction Layer

Courtesy of BMW OF NORTH AMERICA, INC.

Partial spalling (1) of the friction layer has no influence on the function or safety of the brake system (no comfort disadvantages or uneven braking force distribution).

The separation is a purely visual defect, but may cause customer disappointment and uncertainty.

If the pitting/spalling (1) has reached 2x2 mm, these ceramic brake discs can be replaced. They must be returned through the special defective parts channel, as that is the only way that a refund (applicable only to the warranty period) can be made.

Fig 9: Partial Spalling Of Friction Layer

Courtesy of BMW OF NORTH AMERICA, INC.

Return address:

BMW AG

Sonderschadteil Gewahrleistungsteile GWTZ

Heidemannstr. 164

Werk 01.01/Gebaude 23

DE 80935 Munich

For Germany, returns are subject to the PuMA procedure DE4811067.

Friction layer detachment: 

Brake disc with friction layer detachment (1) -> brake disc not OK.

Fig 10: Brake Disc With Friction Layer Detachment

Courtesy of BMW OF NORTH AMERICA, INC.

Fiction layer not fully finished: 

Brake disc (see Fig 11) not OK

Fig 11: Locating Friction Layer Edge

Courtesy of BMW OF NORTH AMERICA, INC.

Gap between friction layer and base 

Brake disc (see Fig 12) not OK.

Fig 12: Gap Between Friction Layer And Base

Courtesy of BMW OF NORTH AMERICA, INC.

Splitting off on outer edges of friction ring: 

Brake disc (see Fig 13) OK.

Fig 13: Splitting Off On Outer Edges Of Friction Ring

Courtesy of BMW OF NORTH AMERICA, INC.

Brake disc (see Fig 14) not OK.

Fig 14: Brake Disc Damage Edge Surface

Courtesy of BMW OF NORTH AMERICA, INC.

Edge pittings in rib area: 

Brake disc (see Fig 15) not OK.

Fig 15: Edge Pittings In Rib Area

Courtesy of BMW OF NORTH AMERICA, INC.

Radial cracks on inside circumference of brake disc ring 

Brake disc (see Fig 16) OK.

Fig 16: Radial Cracks On Inside Circumference Of Brake Disc Ring

Courtesy of BMW OF NORTH AMERICA, INC.

Cracks on rib transition: 

Cracks (1) in rib area of brake disc.

For brake disc, see Fig 17: OK.

Fig 17: Cracks In Rib Area Of Brake Disc

Courtesy of BMW OF NORTH AMERICA, INC.

Brake disc:

Cracks (dimension A) in rib area >20 mm deep -> brake disc not OK.

Fig 18: Brake Disc Cracks Dimension

Courtesy of BMW OF NORTH AMERICA, INC.

Phosphate residue in coolant duct and perforation bore holes/dirt contamination on ASSY  .

Image (A) and (B) -> brake disc not OK.

Fig 19: Phosphate Residue In Coolant Duct

Courtesy of BMW OF NORTH AMERICA, INC.

Brake discs, see Fig 20, not OK.

1. Perforation bore hole.
2. Contamination of ASSY.

Fig 20: Phosphate Residue In Perforation Bore Holes/Dirt Contamination On ASSY

Courtesy of BMW OF NORTH AMERICA, INC.