What is brake fade?
Resins that bind pad compounds together are organic-petro-chemical products. When the Brake Pads reach high temperatures, the resins revert to gas and cause the pads to “aquaplane” on a film of gas (this is called “fade”). The friction force between the brake pad and disc is as a result reduced. Some pads only fade once or twice and then settle down (green fade or bedding-in fade) and then the performance stabilises. Many cheap low quality pads will suffer from continual dynamic fade, sometimes at surprisingly low temperatures.
How does temperature affect brake pad performance?
Generally the performance of the brake pad (friction force between the brake pad and disc) will reduce at high temperatures due to brake fade. The degree and occurrence of this fade will dependent on the quality of the brake pad. The driver of a vehicle will experience the drop off in performance because a higher force will be required to be applied to the brake pedal in order to maintain a constant rate of deceleration.
Will disc (rotor) condition affect pad performance during braking?
Scored, old or worn discs (rotors) can reduce performance because the area of contact of the brake pad with the disc is reduced, thus extending the period for the brake pads to achieve full contact. Therefore it is advisable to skim the discs if they are badly scored or replace them when fitting new brake pads. If they are skimmed the final thickness must not be less than the specified minimum thickness.
Which disc (rotors) should I use?
Good quality discs should always be used. Poor quality discs could be manufactured from poor quality material and not machined to the correct tolerances required. This will result in reduced brake performance and brake shudder.
How long do automotive Brake Pads last?
Generally when fitted to a motor vehicle of approximately ¾ tonnes in street use, 25000 to 35 000km´s is common. This however is very dependant on the use the vehicle has been subjected to and brake pads lasting in excess of 80000 Km is not uncommon. Factors that can reduce the life of brake pads are:
- Weight: Overloading especially commercial applications
- Heat: Excessive hard braking or dragging of pads.
- Poor rotor and brake system condition.
What should I know about friction levels?
A brake pad with a high friction coefficient (approx. 0.5) will generate more brake force than one with a low friction coefficient (approx. 0.25) when the same pressure is applied to it. Therefore in order to achieve a similar braking performance a greater force will need to be applied to the brake pedal when a brake pad with a low friction coefficient is fitted. The friction coefficient often reduces when the brake pads are heated, particularly with poor quality brake pads and this is known a brake fade.
When new brake pads are fitted the brake application often feels soft. This is because there is not full contact between the brake pads and discs and is more prominent if the discs are scored. Some brake pads are more compressible than others and therefore also feel more spongy.
Why are my brakes binding and not lasting on my car?
Brake pads need to move up against the disc in order to generate a braking force. Once the applied pressure is released the brake pads must move away from the disc in order to remove the braking force. If however the brake pads cannot move away binding will occur. One reason for the brake pads not moving away are because the brake pads are oversize and cannot move freely in the brake calliper.
Can hydraulic brake fluid damage the pads?
Yes most definitely. It is vital that the hydraulic system is in good working order. All calliper seals and hoses should be checked for leakages when the pads are fitted. An easy way to check is to look for a sticky area with caked dirt, this will indicate where the leak is coming from in your system. Brake hoses and seals should last 6-8 years under normal conditions.
Why are my brakes squealing, grumbling?
Brake callipers are generally fitted with springs and pins which allow the pads to move freely without rattling and vibrating excessively. They are also fitted with shims between the backing plate and the calliper piston. All these items are fitted in order to eliminate noise, however, due to the dynamic nature of your brake system, these pins, springs and shims wear and lose their tension which can result in brake noise. Worn and scored brake discs can also result in brake noise particularly if new brake pads are fitted without skimming the discs.