Damage to the friction surface on a brake disc can cause adverse and undesirable effects, along with accelerated brake wear and reduced performance. This pictorial guide from Bosch, shows some more common damage types, along with recommendations to correct the cause of the disc damage.

If the cause of the abnormal wear is not corrected, the abnormal wear will continue and damage the replacement brake disc.

Scoring or grooves on the friction surface
Cause    
Dirt particles on brake disc and pad

Effects  
Brake noise
Rubbing effect during braking
Reduced braking performance

Recommendation
When changing the brake discs, always change the brake pads as well

Indentations on the contact surface
Causes   
Improper cleaning of the contact surfaces
Damage to the surfaces through contamination     
Distortion of the wheel hub

Effects
Increased lateral run-out of the brake discs
Chattering and rubbing effects

Recommendation
Clean the contact surface of the brake disc and the wheel hub before mounting new brake discs. Do not use paste lubricants (copper paste, etc.).

Uneven wear
Causes    
Uneven function of the brake calliper
Run-out of the brake disc

Effects 
Poor and/or irregular braking performance
Vibration in the steering wheel
Pulsing effect in the brake pedal

Recommendation
Check the brake calliper and wheel hub when installing new brake discs

Corroded friction area
Causes  
Corrosive substances (e.g. road salt, cleaning agents)            
Damage through water or lack of use – low demand

Effects  
Noise during braking
Irregular braking performance

Recommendation
Replace brake discs and pads. Instruct the customer to occasionally stress the brakes by applying pressure appropriately (bed in the brakes).

Blue surface discolouration
Causes   
Overheating due to jammed/seized brake pads
Vehicle driven with activated or seized parking brake
Brake calliper piston is sticking

Effects  
Rubbing effect during braking
Overheating

Recommendation
Check the entire brake system. Ensure that the brake calliper is functioning properly.

More information on brake servicing can be seen on the Bosch Mobility YouTube channel by search for ”How to change disc brakes“ or by watching the video below.




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