Description of defect: A braking surface of one of the discs is in contact with the metal pad support. Examining the pads it is noted that wear is uneven due to blocking of the caliper (the pads on the other caliper are in perfect condition).

Consequences: The caliper's two pads are completely worn down with consequent onset of noises and vibrations, the brake pedal has to be depressed completely. Braking distance is very long.

Advice: Check, repair or replace the caliper. Replace all discs and pads.

Description of defect: Presence of a very fine deposit of friction material on the disc surface which now has a shiny finish (corrosion has then caused the detachment of part of this layer).

Consequences: Loss of braking efficiency, braking distances too long. The pedal is very stiff but with no braking action.

Advice: Replace discs and pads. Use high, original, quality pads.

Description of defect: The two pads were not positioned in the same manner with respect to the disc. Wear has not been the same for both surfaces. Heat spots can be noted at the centre of the braking surface due to high thermal exposure. The caliper and/or the pads were not fitted properly.

Consequences: Gradual onset of vibrations due to the heat spots. Possible appearance of cracks.

Advice: Check and, if necessary, repair the calipers. Check the pad model and friction material quality.

Description of defect: Deep scores caused by penetration of foreign bodies between pads and disc can be noted. This can be due to unsuitable pad material or the presence of badly distributed abrasives in the mixture.

Consequences: Very unpleasant noise both during braking and when travelling. Diminished efficiency as a result of the reduced contact surface between disc and pads.

Advice: Replace discs and pads.

Description of defect: The braking surfaces are completely covered by very dark spots. These spots are due to deposits of pad friction material. This causes overheating which in turn leads to a transformation of the cast iron with the formation of very hard cementite.

Consequences: Onset of vibrations that become progressively worse.

Advice: Only install friction material that is suited to the brake and vehicle.

Description of defect: The braking surface only shows wear in the outer area. The inner area never comes into contact with the pads as indicated by the presence of corrosion (rust). This situation could be caused by:

- incorrect installation of the caliper and hence the pad which does not make full contact with the disc

- loss of part of the friction material • fitting of wrong pads

Consequences: Reduced braking torque. Increase in operating temperature as the surface on which the pad works is reduced (by about 50% in this example) compared to its normal working surface. There is a risk of localised overheating and therefore the onset of hot judder-type vibrations. Moreover, reduced system efficiency leads to high stress levels and therefore rapid and/or uneven wear (cold judder).

Advice: check the installation and correct functioning of the caliper. Check the fitting and condition of the pads. Check that the pad model is suitable for the particular vehicle.

Description of defect: This disc shows a deterioration that is the sum of defects described in 2 and 6 above. In this case the pad only acts on the inner section of the braking surface. High stress has led to overheating, vitrification (deposit) and detachment of friction material.

Consequences: Progressive reduction in efficiency of the system and, when friction material detaches, total inefficiency of the system.

Advice: As for 2 and 6.

Description of defect: The pads only act on the central section of the braking surface. They may be curved.

Consequences: Reduced braking action with the consequences described in points 6 and 7.

Advice: Check pad planarity and the functioning of the calipers.