Damage assessment of disc brake pads on commercial vehicles: Identifying the causes, preventing any damage

Types of damage to commercial vehicle brake pads

Brake pads on commercial vehicles are subjected to high thermal and mechanical stresses. Signs of wear and damage, such as uneven abrasion, cracking or delamination of the friction material, can provide important clues to problems in the braking system. A professional damage assessment helps workshops to quickly identify the actual cause. This is because the causes often lie not with the brake pads themselves, but may, for example, be triggered by stiff brake callipers or malfunctions in the electro-pneumatic braking system. The following overview shows the most common types of damage to disc brake pads, their possible causes, and also recommended measures for a quick and reliable diagnosis.

Overheating / Material damage

The friction material shows cracks, signs of rust and/or white edges

Possible causes:

Intensive braking
High thermal stress caused by problems with the brake callipers and/or brake discs
Overloaded vehicle
EBS malfunction

Effects:

Overheated friction material becomes brittle and cracks
Poor braking performance
Premature wear and tear
Delamination of friction material possible

Remedy:

Check the causes of overheating
Check the brake callipers and brake discs
Replace brake pads

Uneven wear

Brake disc edge

Uneven wear groove on inner and/or outer radius

Possible causes:

New brake pads fitted to a heavily worn brake disc with a wear edge

Effects:

Reduced braking performance
Squeaking noises and rubbing
Overheating and premature wear
Delamination due to shear forces possible

Recommended measures:

Replace brake pads
Replace brake discs or rework them

Inside a brake calliper

Difference in thickness between inner and outer brake pads

Possible causes:

Guides that are stuck or stiff
Brake piston stuck or stiff
Brake calliper does not return to its rest position

Effects:

Brake imbalance
Overheating and/or premature wear
Reduced braking performance

Recommended measures:

Check/replace brake calliper
Replace brake pads

Within an axle

Difference in thickness between the brake pads on the same axle

Possible causes:

Brake calliper stuck or stiff
Faulty brake chamber
EBS malfunction

Effects:

Vehicle pulls to one side
Overheating and premature, increased wear
Reduced braking performance

Recommended measures:

Check the brake callipers
Check the brake chambers
Check EBS/ABS
Replace brake pads

Uneven wear – diagonal or slanted pad wear

Diagonal pad wear

Brake pad shows uneven wear on one side

Possible causes:

Warped brake calliper
Stiff guides
Damaged or dirty pad seats

Effects:

Noises
Overheating
Uneven braking pressure

Recommended measures:

Replace pads
Check or replace brake calliper

Uneven wear / grooved pattern on the brake pad

Grooves on the brake pad

The surface of the pad shows definite grooves

Possible causes:

Scoring marks caused by excessive wear
Dirt or foreign objects between the brake disc and the brake pad

Effects:

Reduced braking performance
Noises and rubbing
Incomplete contact between brake pad and disc
Overheating and premature wear

Recommended measures:

Replace pads
Service or replace brake discs

Thermal delamination

Partial or complete delamination of the friction lining as a result of high thermal stress

Possible causes:

Intensive/aggressive braking
Overloading
Faults with the brake disc or brake calliper
EBS malfunction

Effects:

Poor braking performance
Noises
Brake pad completely damaged

Recommended measures:

Replace pads
Check brake discs and callipers
Check EBS/ABS

Mechanical delamination

Partial or complete separation of materials for mechanical reasons

Possible causes:

Wear edge on the brake disc
Incorrect fitting
Faulty or seized brake calliper
Excessive play

Effects:

Reduced braking performance
Noises
Brake pad completely damaged

Recommended measures:

Replace pads
Check the disc and brake calliper

Surface cracks

The brake pad has small cracks on its surface

Possible causes:

High thermal stress caused by intensive braking
Sticky brake calliper

Effects:

Vertical, hairline cracks do not pose an immediate safety risk, but nevertheless
Replacement recommended

Recommended measures:

Investigate the causes
Replace brake pads

Surface glazing

The surface of the friction lining is glazed.

Possible causes:

Short-term, intermittent overheating
Excessive use of the brakes during the running-in period

Effects:

Temporary reduction in braking performance
Noises and rubbing sound during braking

Recommended measures:

Mild glazing: no action required or for brake pads in new condition, lightly sand the surface evenly
Heavy glazing: Replace brake pads, check brake discs

Surface contamination

The surface of the friction lining is heavily contaminated with foreign matter

Possible causes:

Oil, grease or other kinds of foreign matter
Leaks from adjacent assemblies
Contamination during maintenance

Effects:

The vehicle pulls to one side during braking
Reduced braking performance

Recommended measures:

Identify and then eliminate cause
Replace pads

The types of damage, their causes and the measures to take described here are provided solely for general information and they also serve to assist with the diagnosis of brake components. They are not intended to replace the vehicle or component manufacturer’s specifications, nor a professional inspection carried out by qualified workshop staff.

All maintenance, repair and servicing work on braking systems is to be carried out in accordance with the relevant manufacturer’s instructions. The actual cause of the damage may vary depending on the vehicle, operating conditions and the condition of the braking system. No liability is accepted for the completeness, accuracy or applicability of the information provided.

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