Brake Fade or Long Pedal??
5-minute read
Introduction
In the motorsport braking industry it is very common for people to mix up ‘brake fade’ with ‘a long pedal’. This page will dive into these issues along with causes, symptoms and potential solutions. But in summary:
BRAKE FADE is where your brake pedal is still ‘up’, but the brakes lose effectiveness which is caused by a loss of friction at the pad/disc interface.
A LONG BRAKE PEDAL is where the pedal travel increases which can result in loosing braking caused by fluid ‘boiling’ or mechanical and/or hydraulic issues.
Whilst these two issues are not the same it is important to note that one can cause other!
What are the causes of brake fade?
Temperature is the culprit in most cases. If your brakes are too hot the interface between the pad and disc starts to deteriorate – which can be pad material breaking down or a buildup of gases generated by the materials involved getting between the pad and disc causing a ‘barrier’ that restricts the effectiveness of the pads.
Introducing too much temperature in the first place can be caused by a lot of different inputs, such as brake pad quality, disc type, cooling, driving style, mechanical issues, condition of hydraulic system including caliper seals, master cylinder seals etc and more! To give one example, if your calipers are not serviced properly, there can be stiction around the seals causing the pistons to not retract properly when you take your foot off the pedal, which will cause drag in the brake system which will then introduce more temperature.
The other thing to consider is that temperature issues that cause brake fade can be self-perpetuating. This means that as temperatures increase too much and friction reduces and the brakes begin to fade, most drivers will simply push harder on the brake pedal to try to stop the car. This of course makes the problem worse, and the cycle continues!
How do I fix brake fade?
The only thing to do is to reduce the use of the brakes and cool them as much as possible. This will sometimes bring the temperature back into a good temp window and fix the issue. Sometimes though the problem won’t go away until the brakes are fully cooled. It is important to then analyse how to reduce brake temperature in your car on the ‘track’.
What causes a long brake pedal?
Unless there has been some sort of mechanical problem or failure in your mechanical brake system, the primary cause of brake pedal ‘going long’ – which is a horrible feeling – is by pushing your brake fluid beyond its boiling point. If the fluid is over-heated it will develop small gas bubbles which are compressible. This compression is what will cause the long pedal known as ‘brake fluid fade’.
Most people will be aware that brake calipers have pressure seals in them to keep the brake fluid inside the caliper. These seals end up with a very small amount of brake fluid behind them that is forcing the pistons to push the pads – and hopefully slow your car! What many will not realise is that it is this very small volume of brake fluid that takes most of the punishment from the sometimes very high temperatures in a brake system. Also, this small amount of fluid does not really circulate around the caliper much. So, it gets repeated temperature cycles and will deteriorate and be less able to deal with temperature if not replaced regularly.
Most times, a long brake pedal which is caused by ‘boiling’ brake fluid is something that gets progressively worse, rather than a sudden failure. Like brake fade described above, a long pedal is normally caused by excessive heat. And remember we mentioned above that one issue can cause the other? Imagine you are starting to get brake fade whereby the pads are overheating for example, and you start pushing the pedal harder to try to achieve the stopping power you want. As you are doing this you are also introducing more and more temperature into the brake system, including the brake fluid. If this fluid is not up to the task, it will start to vaporise and pedal travel will increase.
The other common cause of a long brake pedal is ‘brake pad knock-off’. Knock-off happens when the loads passing through the front wheel from high lateral g-forces or hitting a kerb can overly load the wheel bearing which allows movement in the area between the disc and caliper. This movement can cause the disc to ‘knock’ the pad back into the caliper enough that when you get back on the brake pedal, the initial part of the pedal travel is pushing the pads back ‘out’ to the disc face. This means that the pedal is longer than it should be. The good news here is that ‘pumping’ the pedal is normally enough to bring the pedal back. This is why you see drivers checking the pedal down the straights as they bring the brake system back into alignment!
How do I fix a long brake pedal?
Assuming the mechanical system in the car is in good condition and the long pedal is a result of overheating brakes, the only thing to do is cool the brake system, replace the brake fluid with the highest quality you can afford and potentially increase cooling directed at the caliper itself.
Make sure to replace your fluid regularly as brake fluid is hydroscopic (will absorb moisture) so over time it will have higher content of moisture, causing the boiling point to reduce. It is a regular servicing point that should not be overlooked.
Make sure your brakes are bled regularly, particularly after copping a hard time at the track or in the forest and always choose a high-quality fluid to give yourself the best chances of avoiding the dreaded long pedal. More information on brake fluid Here
To solve knock-off issues you need to review your mechanical system. There can be movement caused by under-performing wheel bearings that need replacing or servicing, or a solid kerb strike! To help reduce knock-off you can fit fully floating disc assemblies that allow a certain amount of movement of the brake caliper vs disc and allows this movement without the pads being pushed back into the caliper.
There are a many issues and topics surrounding these brake problems and causes so for more specific information or advice on your car set up, get in touch with us at MSB. We are always happy to help! Contact us for export advice.
