Porshe 911 (997). Manual - part 286

Minimum thickness (x) of the PCCB brake disc

3. Check brake discs for minimum thickness -x- . The minimum thickness of the brake disc (example:

Min. Th. 33.7 mm) is stamped on the brake disc chamber →  Checking brake discs for minimum
thickness.

Edge damage on PCCB brake disc

4. Check brake discs for edge damage -see illustration- (damage caused as a result of improper use)

→  Checking brake discs for edge damage.

General information on replacing worn PCCB brake discs

Three criteria governing the condition of the parts can make replacement necessary depending on the
wear of PCCB brake discs:

1. Surface changes in the brake disc friction surfaces (material fatigue/wear) at an advanced stage (indication

of wear: associated friction surface damage > 1 cm

2

).

2. Surface roughness of the brake disc friction surfaces too great (roughness depends on mileage and load).

3. Brake disc minimum thickness is not attained due to wear (material erosion due to friction).

In practice, all three forms of brake disc erosion usually occur.

• 

Only in rare cases (in the case of long-term race driving brake loads/very high temperatures on the
friction surfaces) does the surface change so quickly that a premature brake disc change has to be
performed.

• 

Blue discs on the brake disc chamber and/or strongly coloured brake calipers indicate a long-term,
sustained high load, on a racing circuit, for example.

• 

Diagnostic system: reading out fault memory and activating systems

Basic information

1301

Replacing brake discs (notes/decision-making aid)

When replacing brake discs as a result of wear (see wear assessment) both brake discs must be replaced on an
axle!
Irrespective of wear, a brake disc change can be necessary on the brake disc friction surfaces due to edge
damage! In such cases, only one brake disc may need to be replaced if the friction area surface of the other
PCCB brake disc is still completely OK →  Checking brake discs for edge damage.

Original (A) and new (B) technology in brake discs

Ensure that brake discs manufactured using the modified technology -B- (used in the 911 Carrera 997 since
production began) are not interchanged with the brake discs manufactured using the original technology -A-
(911 Carrera 4S, 911 Turbo, 911 GT2, 911 GT3 - before model 2005). Distinguishing characteristic: Double
the number of ribs between the friction surfaces in brake discs in which the modified technology is used -B-
and modified perforated bore layout.
In addition, the new technology -B- features little wear indicator plates on the friction surfaces (at three
points, each arranged at 120° with respect to one another) and the wear limit (brake disc minimum thickness)
has also been modified. The brake disc minimum thickness is stamped on the brake disc chamber (example:
Min. Th. 33.7 mm).
Install only brake discs that have been manufactured using the new technology in the -B- 911 Carrera (997).
In general, the following applies to PCCB brake discs: A combination of the two technologies -A and B- on
one axle is not permitted! A front axle/rear axle mix of the two technologies -A and B- is possible.

Cracks (stress-relief microstructure) in the brake disc friction surface

Diagnostic system: reading out fault memory and activating systems

Replacing brake discs (notes/decision-making aid)

1302

Stress-relief microstructure in PCCB brake disc friction surfaces

Cracks in the brake disc friction surfaces are viewed differently to cracks in cast iron brake discs. Cracks in
PCCB brake discs do not constitute a wear criterion but exist already in new brake discs because of the way in
which they are manufactured.

Note

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.

• 

The stress-relief microstructure results from the way in which the brake disc surface is manufactured
and does not pose a risk to safety. 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
chamber side and the side that is opposite to the chamber can differ significantly from one another.

• 

Note concerning bores (perforations) in the brake disc friction surface

Diagnostic system: reading out fault memory and activating systems

Cracks (stress-relief microstructure) in the brake disc friction surface

1303

Bores (perforations) in brake disc friction surface

Observe the following warning when cleaning or exposing the bores in the brake disc friction surface!

ATTENTION

PCCB (Porsche Ceramic Composite Brake): Risk of damage to the brake discs as a result of
impermissible work on the bores in the brake disc friction surface.

Damage to brake discs

• 

→ Clean the bores on PCCB brake discs with high-pressure cleaning equipment (only if necessary).

In doing so, observe environmental and safety regulations.

→ Do not machine (boring or countersinking is not permissible).

Coating on the PCCB brake discs (potential causes)

Bores (perforations) in brake disc friction surface

The coating on the PCCB brake discs arises as a result of a high load and high temperatures, for example on a
racing circuit. Check the following in such cases:

Ventilation (brake cooling): all components are present, secured correctly and undamaged.

• 

Brake pad quality: use the appropriate brake pads if the vehicle is being used on a racing circuit.

• 

Perforated bores -see illustration- in the brake discs must be free. Expose them if necessary →  Notes
on bores (perforations) in the brake disc friction surface.

• 

The brake discs can still be used even if there is a coating on them provided that they are OK with
respect to all wear criteria →  General information on replacing worn PCCB brake discs. The
perforated bores -see illustration- must be free.

• 

Note on bedding in the new brake pads

New brake pads require a slightly longer bedding-in period for PCCB brake discs than cast iron brake discs.
In general, the following applies: New brake pads must be broken in (bedding-in period), their optimum
braking effect is therefore not reached until after a few hundred kilometres. The slightly reduced braking
effect must be compensated for by increased pressure on the brake pedal. The same also applies after a brake

Diagnostic system: reading out fault memory and activating systems

Note concerning bores (perforations) in the brake disc friction surface

1304