Porshe 911 (997). Manual - part 287

 

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Porshe 911 (997). Manual - part 287

 

 

disc change.

Checking PCCB brake discs (wear assessment)

Visual inspection of the surfaces of the brake disc friction surfaces
(indication of wear)

Note

The friction surface changes occur due to material fatigue as a result of extremely high thermal load.
These disc temperatures, which occur above all in racing conditions, cause a progressive material
fatigue.

• 

Effects on driving: The surface change worsens the smoothness of braking, decreases the disc
strength and increases the brake pad wear and therefore makes a precautionary parts replacement
necessary.

• 

The following illustrations (PCCB brake disc wear appearance) are to be used for damage assessment.
PCCB brake disc wear appearance

PCCB brake discs without surface fractures

1. Friction area surface after normal brake load in road use. No surface

fractures.

No replacement
necessary!

Diagnostic system: reading out fault memory and activating systems

Note on bedding in the new brake pads

1305

PCCB surface fractures

2. Friction area surfaces after a long run and occasional higher load. Isolated surface fractures smaller than 1

cm

2

-arrow-

 .

No replacement necessary as the associated surface fractures are < 1 cm

2

!

PCCB friction surface damage

3. End of service life of friction area surface or after highest load on a racing circuit.

Replace brake discs if there is associated friction surface damage > 1 cm

2

-arrow-

 . To do this, please

observe the relevant information →  Replacing brake discs (notes/decision-making aid).

Evaluating surface roughness (Sr) (max. 80 micrometre permitted)

Note

An increase in surface roughness impairs smoothness of braking (rubbing, shaking in steering wheel,
scraping noises) and increases brake pad wear.

• 

With a roughness (Sr) value of > 80 µm (> 80 micrometre), a precautionary parts replacement is
required.

• 

The assessment is carried out visually, based on the diagram. Two illustrations of the same peak-to valley
surface roughness (views 1 and 2) help to make a better assessment.

1. Brake discs that are OK:

Diagnostic system: reading out fault memory and activating systems

Visual inspection of the surfaces of the brake disc friction surfaces(indication of wear)

1306

PCCB surface roughness (Sr) = 6 micrometre (view 1)

1.1. Surface roughness (Sr) = 6 µm -see illustration- (view 1)

PCCB surface roughness (Sr) = 6 micrometre (view 2)

Surface roughness (Sr) = 6 µm -see illustration- (view
2)

New brake disc. Illustration is used to enable better
classification.

The early stages of roughness are indicated by burnt-out carbon fibres on the surface of an otherwise
intact, semi-matt surface.

The surface feels
smooth.

PCCB surface roughness (Sr) = 56 micrometre (view 1)

1.2. Surface roughness (Sr) = 56 µm -see illustration- (view 1)

PCCB surface roughness (Sr) = 56 micrometre (view 2)

Diagnostic system: reading out fault memory and activating systems

Evaluating surface roughness (Sr) (max. 80 micrometre permitted)

1307

Surface roughness (Sr) = 56 µm -see illustration- (view
2)

In the advanced stages of fibre burn-out and the initial destruction of the Si and SiC 'matrix', the
depressions have become more pronounced. Large sections of the surface are still intact, the
depressions form an even, fine-grained pattern.

The surface still feels matt, however, and the roughness is not yet
pronounced.

No replacement
necessary!

PCCB surface roughness (Sr) = 72 micrometre (view 1)

1.3. Surface roughness (Sr) = 72 µm -see illustration- (view 1)

PCCB surface roughness (Sr) = 72 micrometre (view 2)

Surface roughness (Sr) = 72 µm -see arrow- (view
2)

Borderline disc, which can still just be evaluated as OK. As a result of more advanced damage to
the surface, the depressions are larger, and above all deeper, compared with the previous surface
condition.

On the one hand, the more extensive roughness is noticeable (only when a comparison is made); on the
other hand, however, like before, "only" depressions are observed.

Replacement not yet
necessary!

2. Worn brake discs:

Diagnostic system: reading out fault memory and activating systems

Evaluating surface roughness (Sr) (max. 80 micrometre permitted)

1308

 

 

 

 

 

 

 

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