Imagine this, you’re driving your BMW as usual to work in the morning and you arrived at a junction. You step on your brake and you can hear a loud screeching noise. You start to wonder, what’s wrong with my car? This edition of the Vebo blog explains about potential issues with a car brake, why it happens and how do we solve it.
Apart from the scenario above, you may also experience one of the brake issues:
1) iDrive shows that there is still remaining % of brake pad but there is metal grinding sound indicating the brake have worn out especially on the rear brake
2) Electric parking brake failure
3) Steering starts to wobble you brake
The diagram below illustrates the components of a car brake. The brake stops a car by converting kinetic energy into heat. The rubbing of the friction material on a brake pad to the disk causes this energy conversion and ultimately stops the car from moving forward.
From the brake bad structure below, you'll notice that the friction material is the only component that has direct contact to the disc. The friction material will wear out over time. The other components such as the adhesive, insulation zone and steel back are just the supporting component and not mean to touch the disk brake.
Now that we understand the basics of how brakes work, let’s see what sort of brake issue that we are seeing daily for brake replacement job.
From the photo below, you may notice that the used disc is scratched when compared to the brand new disc.
So what scratches the disc? From the image below, you would notice that when the friction material wears out, the steel back will have direct contact with the disk. Metal to metal contact is the reason for screeching sound and deep scratches on the disk.
So lets see the opposite side of the brake pad as all brake pads work in pair.
Are you surprised to see that the outer brake pad is fully worn down but the inner pad which is connected to the sensor still have at least 20% remaining? This will mislead the driver that the brakes are still in a good condition.
Let’s see another example of unevenly worn brakes.
Let see the opposite brake pad (see image below). The iDrive monitor shows that there’s 78% of brakes left, but due to a really bad uneven wear, the left side steel back starts to scratch the disc.
Lets probe deeper into this what is causing such scary surprise.
One of the reason behind the uneven wear is the brake dust. When the friction material rubs against the disk, dust particles will be formed. This accumulates over time. The video below shows the amount of dust when a worn brake is blown with a high pressure blower.
So with all the brake dust accumulation, it will reduce the efficiency of the brake component to work properly. The brake dust will also cause the brake screeching sound when enough brake dust had been accumulated.
So why does the brake component start to work with less efficiently over time? The simple answer to this is...dust. The images below illustrates dust build ups in the brake components suck as clips, guide, lock pin, and calipers.
The brake pad will move parallel along the guide inside the calipers. When the slot becomes dirty due to the accumulation of the brake dust, it will restrict the brake pad movement which then causes the unevenly worn brake pad.
So how do we tackle this issue?
Our recommendation is the brake system needs to be serviced from time to time to eliminate dust build-up. This is especially important for rear wheels. Typically, most of the cars have a front biased brake force distribution. This means that the rear brakes will have longer life span but the accumulation of the dust will reduce its efficiency.
The next section explores how brake servicing is done.
First, we will remove the dust by blowing high pressure air to it. Alternatively, you can use high pressure water or brake cleaner.
After that we will remove the brake calliper, brake pad and the guide pin and lock pin. And we will remove the brake dust from each of it by buffing with the wire brush.
Greasing the brake pad to ensure it have enough lubrication and protection from dust. This will allow the brake pad to work properly to reduce the uneven wear.
We will also check the thickness of the disk to ensure that it adheres to the minimum thickness spec of the disc provided by the manufacturer.
Always ensure your disk meets the minimum thickness. Failing to meet will result in vibration while braking hard. Since each disc can last 2 brake pad changes, it’ll last about 100,000km before it fall to the minimum thickness. However, if the disk is scratched, then there would be a need to replace it.
Finally we will reinstall the brake components. The brake components looks brand new after cleaning.
As a conclusion, it all boils down the time and cost of maintaining the brake kit. By servicing the brake at 30,000KM intervals, drivers can expect a longer brake system(including electronic parking brake actuator) life expectancy, brake noise reduction and uneven wear.
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