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Diagnosing brake problems

Here you can find useful and valuable repair tips regarding damage assessment on brake discs, brake pads as well as wheel suspension and steering

Failure modes of brake discs and brake pads

Important safety information
The following technical information and practical tips have been compiled by HELLA in order to provide professional support to vehicle workshops in their day-to-day work. The information provided on this website is intended for use by suitably qualified personnel only.

 

DIAGNOSING BRAKE PROBLEMS: FAILURE MODES OF BRAKE PADS: NOTES

Friction lining comes loose from the base plate

The friction lining has come loose from the lining's base plate, either in full or in part.

 

CAUSE

  • Thermal or mechanical overload 
  • Subsurface corrosion between lining and base plate
  • Insufficient fitting accuracy of the brake pads
  • Damage to the brake pad due to incorrect handling or installation
  • Non-compliant brake pads

 

 

EFFECT

  • Grinding noises when not pressing the brake
  • Squeaking during braking
  • Deficient braking characteristics
  • Breakdown of friction lining due to thermal overload

 

REMEDY

  • Clean the brake caliper and check for proper function ✓
  • Check the brake caliper and pad for fitting accuracy ✓
  • Replace the brake pads and accessory parts if necessary ✓

Thermal overload

Brake pad has been damaged due to overheating. Binder in the pad has been destroyed and the pad material is breaking down. The surface is porous and glazed in parts.

 

CAUSE

  • Sticking or tight guide sleeves
  • Brake piston stuck within the brake caliper
  • Extreme driving conditions or sustained braking
  • Sticking brake pad

 

EFFECT

  •  Noises
  • Poor braking function

 

REMEDY

  • Clean the brake caliper and check for proper function ✓
  • Check the brake caliper and pad for fitting accuracy ✓
  • Replace the brake pads and accessory parts if necessary ✓
  • Check the brake discs and replace them if necessary ✓

Grooves in the friction lining

The pad surface has deep grooves and wear edges.

 

CAUSE

  • New pads have been installed on the old, worn brake discs
  • Foreign bodies between the brake pad and disc
  • Environmental influences (salt, dirt, etc.)

 

EFFECT

  • Noises when operating and not operating the brake
  • Poor or one-sided braking function

 

REMEDY

  • Clean the brake caliper and check for proper function ✓
  • Replace the brake pads, accessory parts and brake discs ✓

 

Material and edge chunking on the friction lining

The friction lining is damaged. The lining material has broken off at the edges.

 

CAUSE

  • Incorrect installation
  • Incorrect, non-compliant brake pads
  • Lack of freedom of movement for the brake caliper
  • Mechanical overload
  • Thermal overload

 

 

EFFECT

  • Noises
  • Poor braking function
  • Premature wear

 

REMEDY

  • Clean the brake caliper and check for proper function ✓
  • Replace the brake pads ✓
  • Check the brake caliper and pad for fitting accuracy ✓
  • Check the accessory parts and brake discs and replace them if necessary ✓

 

Excessive wear

Brake pads are heavily worn and have worn down to the base plate in some cases.

 

CAUSE

  • Deficient maintenance
  • Exceeding the inspection intervals 
  • Sustained braking during downhill driving
  • Sticking or tight guide sleeves
  • Brake piston stuck within the brake caliper
  • Extreme driving conditions or sustained braking
  • Sticking brake pad

 

EFFECT

  • Noticeable noises when operating and not operating the brake
  • Poor braking characteristics
  • Damage to other wheel brake assemblies due to thermal overload 

 

 

REMEDY

  • Disassemble the brake system and check it ✓
  • Clean the brake caliper and check for proper function ✓
  • Check the caliper guides, dust covers and damping sleeves and replace them if necessary ✓
  • Replace the brake pads, brake discs and accessory parts ✓

Uneven lining wear

The brake pads on one side of the wheel brake have been worn down unevenly.

 

CAUSE

  • Sticking or tight guide bolts or caliper guides on the brake caliper
  • Brake piston stuck within the brake caliper or brake pad wedged in the caliper slot

 

EFFECT

  • Noises
  • Uneven braking characteristics
  • Premature wear due to mechanical and thermal overload

 

REMEDY

  • Disassemble the brake system and check it ✓
  • Clean the brake caliper and check for proper function of the individual components ✓
  • Check the brake caliper and pad for fitting accuracy ✓
  • Replace the brake pads and, if necessary, the accessory parts and brake discs ✓

Glazing of the friction lining

The friction lining has a hard, smooth, polished-looking surface that reflects incident light and is similar to a glass surface. This defect generally occurs on new brake pads with minimal time in service.

 

CAUSE

  • Overload of the brake pads in the bed-in phase
  • Repetitive high temperature change on the brake pad at short intervals
  • Long braking phases with low pedal pressure

 

EFFECT

  • Loss of friction on the brake pad, leading to poor braking function
  • Insufficient or one-sided braking function at the affected wheel brake
  • Noises (squeaking) during braking

 

REMEDY

Replace the heavily glazed or damaged brake pads. Check the brake discs and replace them if necessary. 

 

Brake pads with short time in service:

  • Grind the friction lining surface evenly ✓
  • Compare the thickness of all the brake pads and check for reusability ✓

 

Contamination of the friction lining surface

Brake pad has been contaminated by grease, oil or other foreign substances.

 

CAUSE

  • Deficient maintenance work
  • Defective drive shaft joints
  • Leak in hydraulic brake system

 

EFFECT

  • Insufficient or one-sided braking function
  • Braking causes noise

 

REMEDY

  • Disassemble, check and clean the wheel brake of the affected axle ✓
  • Determine and correct the cause of the contamination ✓
  • Clean brake pads with sufficient thickness and grind the surface evenly ✓
  • Replace heavily contaminated or worn brake pads ✓
  • Complete the brake system and check for proper function ✓•

DIAGNOSING BRAKE PROBLEMS: FAILURE MODES FOR BRAKE DISCS: NOTES

Heat cracks

The friction ring of the brake disc has vertical cracks running all the way through from the edge to the disc chamber.

 

CAUSE

  • High alternating mechanical and thermal load
  • Overload of the brake disc in the bed-in phase due to force or sudden, hard braking
  • Use of the brake disc beyond the wear measurement
  • Brake discs of unknown origin with poor quality

 

EFFECT

  • Reduced braking function
  • Knocks at the steering wheel
  • Pulsing brake pedal

 

REMEDY

  • Replacing the brake discs
  • Check the condition of brake pads and check for wear; replace if necessary

 

Always follow the maintenance and repair instructions from the respective vehicle and brake manufacturers in this regard! 

Striations and grooves on the friction ring

The friction ring of the brake disc has horizontal striations or grooves on the contact surface.

 

CAUSE

  • Contamination or foreign bodies between the brake pad and disc
  • Brake pad of unknown origin with poor quality 

 

EFFECT

  • Reduced braking function
  • Noises
  • Increased wear

 

REMEDY

  • Clean the brake caliper and check for proper function
  • Replace the brake discs and brake pads.

 

Always follow the maintenance and repair instructions from the respective vehicle and brake manufacturers in this regard!

Different disc thickness/difference in thickness

The brake disc has a different disc thickness spread over its circumference. These deviations in geometry are also referred to as a difference in thickness. (DTV - Disc Thickness Variation).

 

CAUSE

  • Poor concentricity of the wheel hub or brake disc
  • Erroneous or improper installation of the brake disc on the wheel hub
  • Insufficient cleaning of the contact surface on the wheel hub
  • Long brake disc period of use with excessive axial runout

 

EFFECT

  • Wobbling motion of the brake disc
  • Axial runout with simultaneous low brake load
  • Brake judder

 

REMEDY

 

Always follow the maintenance and repair instructions from the respective vehicle and brake manufacturers in this regard!

Subsurface corrosion of the contact surface

The disc chamber is corroded in places at the contact surface to the wheel hub.

 

CAUSE

  • Installation error
  • Insufficient cleaning of the contact surface on the wheel hub

 

EFFECT

  • Poor concentricity and axial run-out of the brake disc
  • Difference in thickness of the friction ring
  • Brake judder

 

REMEDY

 

Always follow the maintenance and repair instructions from the respective vehicle and brake manufacturers in this regard!

BRAKE DAMAGE ASSESSMENT FOR WHEEL SUSPENSION AND STEERING: NOTES

Influence of defective components on braking characteristics

Damaged or improperly function components in the wheel suspension or steering can affect not just the driving characteristics but the braking characteristics of the vehicle as well. If unusual noises, vibrations or unstable driving characteristics are detected during braking, the potential cause can stem from different vehicle components.

 

EFFECT OF DEFECTIVE COMPONENTS

Defective shock absorber and tires

  • Degraded traction
  • Declining braking function
  • Lengthened braking distance

 

Defective or improperly installed rubber bearings

  • Unstable driving characteristics
  • Steering wheel or pedal vibrations
  • Knocking noises

Lack of damping due to damaged or leaking hydraulic support

  • Knocking noises
  • Brake judder
  • Vibrations
  • Unstable driving characteristics

 

Defective coupling rods, transverse control arms or stabilizer suspension

  • Knocking noises
  • Unstable driving characteristics
  • Vibrations

 

Defective or improperly installed rubber sleeves at the drive shafts

  • Leaking grease contaminates adjacent assemblies