Light vehicles



There are many different types of brake noise. Here are explanations for each, with our recommended remedies.

Brake noise typically originates from vibration on a part within the wheel end section of the vehicle – between the tyre and the connection to the chassis. Noise is often blamed on the brake pad itself, but can come from any part, from the wheel bearing to the ball joint. Within the brake system, it's normal to have some vibration, but it is not usually intense enough to be audible.

TYPES OF NOISE EXPERIENCED BY DRIVERS

LOW FREQUENCY VIBRATIONS – JUDDER

1 

DESCRIPTION

A deep noise with frequency below 300 Hz.

CAUSES

  • Poor tolerance
    (poor fitment on the hub or excessive disc thickness variation).
  • Disc damage

SOLUTION

Replace the disc and clean and lubricate all surfaces of the brake assembly according to the vehicle manufacturer's instructions.

 

MEDIUM FREQUENCY VIBRATIONS – SQUEAL

2

4

DESCRIPTION

Noise with frequency in the range 300 - 5.000 Hz.

CAUSES

  • Sticky movement on the caliper piston,
  • non-planarity of the working surface of the disc,
  • pad fitting errors,
  • incorrect allocation of anti-noise fixings (eg. shims),
  • disc thickness too low.

SOLUTION

  • Clean and lubricate components of the caliper,
  • ensure disc planarity (once fitted on to the hub) will stay within a tolerance of 0.1 mm.
  • Clean the hub surface, machine disc surface,
  • replace disc and make sure brake pads,
  • shims and accessories are fitted properly.
  • Consider damping noise intensity with shims or brake pads with noise-reduction features.
 

HIGH FREQUENCY VIBRATIONS – SQUEAK

DESCRIPTION

Noise with frequency higher than 5 kHz

CAUSES

The most common reason for a squeak is a molecular vibration within the friction material during application to the brake disc.

SOLUTION

Replace the brake pad set. Also check that the accessories (e.g. the caliper clips) are correct and properly fitted

 

VERY HIGH FREQUENCY VIBRATIONS – ULTRASOUND

DESCRIPTION

Noise with frequency higher than 12 KHz, greater than the upper limit of human hearing.

 

FRICTION SURFACES GIVE VITAL CLUES

The appearance of the friction surfaces can give a good indication of the causes of noise problems. Jack up the vehicle, remove the pads and examine the friction surfaces to analyse potential problems. Below are five symptoms that relate to noise.


 

SYMPTOMS AND REMEDIES

TAPERED PADS

  

APPEARANCE

Uneven wear, tapered pads

CAUSE

Distorted caliper, caliper slides sticking, excessive caliper clearance

EFFECT

Premature pad wear, uneven braking pressure, noise

REMEDY

Replace pad set, maintain & service caliper

 

UNEVEN WEAR

  

APPEARANCE

Uneven wear on pad surface

CAUSE

Irregularly worn brake disc (a wear lip will be visible on the disc)

EFFECT

Squeal & judder, premature pad wear

REMEDY

Replace brake discs and pads

 

UNEVEN WEAR WITHIN AXLE

  

APPEARANCE

One or more brake pad within the axle set will be excessively worn

CAUSE

Caliper guide pins or piston sticking

EFFECT

The vehicle pulls to one side while braking, uneven & rapid pad wear, squeal & judder

REMEDY

Maintain all caliper slides & pistons, replace pads. Check discs

 

DAMAGED BACK PLATE

  

APPEARANCE

Damaged back plate

CAUSE

Incorrect assembly, excessive force used during fitting

EFFECT

Braking inefficiency, irregular wear, noise & judder

REMEDY

Replace full brake pad set

 

PISTON DAMAGE

  

APPEARANCE

Anti-noise features (rubber-coat / shim) damaged by piston

CAUSE

Piston not retracting fully, heavy brake use

EFFECT

Overheating, noise

REMEDY

Replace brake pad set, maintain caliper


 


 

AVOIDING NOISE PROBLEMS

The easiest way to avoid problems is to ensure that the brake pads and caliper are correctly assembled.

Tips for correct assembly:


 
  • Strip and clean all the caliper slides and pins. 
     
 

 
  • Emery paper can only be used on the caliper and pad abutments in the case of heavy rust or pollutants. 
    Note: if the caliper is not sliding easily, this can result in tapered pads or uneven wear within the axle, which creates squeal and judder.
     
 

 
  • The pins must have the correct lubrication to ensure free movement so that the pin does not seize into the caliper body. Also, check the condition of the slide pin rubber boots to stop water ingress. 
    Note: if the pins are not lubricated they may seize, causing wear taper and noise issues. 
     
 

 
  • Check for free piston movement, and retract the piston fully – this is essential to avoid damage to the shim or the rubber coat. 
 

 
  • Check that the brake pads fit freely and easily into the caliper brackets. 
     
 

 
  • Clear burrs off the brake pad edges if required. 
    Note: if the pad is not moving freely inside the brackets, there will be ongoing contact with the discs, causing squealing as well as tapered pads or uneven wear within the axle. 
     
 

 
  • In certain cases (e.g. an old rusted caliper), it is a good idea to lightly lubricate the contact points between metal back plate and slides with copper grease, according to the vehicle manufacturer's instructions. 
    Note: take care that NO grease touches the friction material. 
 

 
  • Insert wear indicators, when appropriate, in or on the brake pads. 
     
  • Screw in the caliper fixing-bolts. 
     
  • Replace the thread-lock bolts with new ones. 
     
 

 
  • Follow the correct tightening torque and sequence recommendations.
  • With the brake caliper reassembled, pump the brake pedal until the stroke is around one third of the full stroke potential.
  • Check that the brake operates correctly, including pad retraction. 
     
  • Refit road wheel. If there is free rotation, the vehicle is ready to go back on the road. 
    Note: do a road test before returning the vehicle to make sure that the brake system is in full working order. When you return the car to the driver, advise them on the correct bedding-in procedure to ensure proper brake efficiency. We have created a handy. 
    Driver Tips leaflet you can use for this purpose – ask your local representative.
 

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