BRAKE PAD SQUEAL AND OTHER NOISE PROBLEMS
Basically the noises heard from the brake systems (assuming that the pads are not simply worn out) are dividable into two types of noise.
GRINDING SOUND and BREAK SQUEAL.
Brake squeal is a common problem and is the nightmare of all pad manufacturers. It is caused when the pad “bounces” in a calliper and the squeal noise is resonance between the back plate and the piston. The grinding noise that is sometimes heard (more frequently with semi metallic not Asbestos pads) is somewhat unnerving and sometimes tends to sound as though the pads are completely worn out. The third noise, which can come from the brake system, is after the fitting of grooved or drilled brake rotors, which can be a whirring or aeroplane type sound.
- We have found that the fixes for all of these problems are as follows;
Applying plastic shims to the rear of the pad can dampen this, but these are expensive and to fit them on every pad where the incidence of brake squeal can be only 1 in 10 is false economy. These are however, available, as a low cost accessory item. We definitely do not recommend the use of general workshop greases, especially Copaslip on the back of brake pads as these are a friction reducing agent being applied in the area of the only part of your vehicle which is designed to produce friction – the brakes. There are however, some “paint on” anti squeal silicone/rubber based materials, which are viscous enough to stay where they are placed and are useful in reducing brake squeal.
On certain BMW and Audi calliper fitments, we have found that applying a 5mm or 1/4 inch chamfer at the front and back leading edges of the pad has the effect of completely reducing the squeal. (Many OE pads ARE chamfered in this way). This is a fix, which needs to be done by a knowledgeable workshop mechanic if the problem arises, but the measurements above should not be exceeded. As our pads are TOTALLY ASBESTOS FREE, there is no health hazard with the dust generated bearing in mind our dimensions mentioned above are maximums and a normal dust mask is advisable.
One of the MOST PROMINENT REASONS causing brake squeal on used cars is poor disc condition. Pads will often make a noise due to vibration whilst bedding in. The worse the condition of the disc obviously the longer it takes to bed in and the longer the noise continues. Pads that have not achieved a 90% SURFACE AREA CONTACT with the disc will ALWAYS squeal.
- We have seen plenty of examples where pads just sit on a small lip on the outer and inneredge where the used disc was badly “troughed” and was not replaced or re-skimmed.
Turning or skimming of rotors is also recommended if not replacing discs as this removes the glaze and polish from the surface of the discs, which can also promote brake squeal.(Always observe the disc minimum thickness, which is in our published catalogues for safety reasons and to avoid disc overheat).
GRAUNCHING or GRINDING SOUNDS Can be down to the material itself, happily we have had very few complaints of this on our pads. We have found that by putting a centre line groove in the pad, this can contribute to reducing this noise. We have therefore adopted a programme of centre line grooving on a large number of pads to reduce the incidence of this problem. The addition of the centre line groove also totally eliminates any pad cracking in the centre surface area of the pad where maximum heat is generated and “bulging” can occur.
BRAKE ROTOR NOISE
Created by rotors with holes or grooves, this sound is usually at its loudest when the discs are first installed and does drastically reduce after a few hundred kilometres, when the pad becomes flat and seated on the disc. This is not a warrantable situation and is normally “part of the programme” as we say and has to be accepted by customers ordering grooved and slotted discs.
SOLUTIONS WHEN NOISE OCCURS
- 1) Check rotor condition and “turn” or replace.
- 2) Allow pads to bed in properly.
- 3) Apply 5mm chamfer at left and right edges.
- 4) Use anti squeal backing if available.
- 5) NEVER “sand” friction material faces to eliminate noise.