Is it better to change the brake pads and brake discs at the same time?
by Shop Dixcel on Mar 15, 2022
This is one of the most frequently asked questions. The answer is YES.
For example, the brake discs do not need to be changed if the car is relatively new and there is still a lot of disc life left. They absolutely need to be changed if the discs are unevenly worn or badly scored.
Take a look at the braking surface of the discs. There are ridges on the edges of the braking surfaces. The following is a simple illustration
The points that are circled in RED are only points that the brake pad is in contact with the braking surface of the brake disc. If the brakes are in this condition, the braking power is obviously reduced, and it can even cause brake noise.
Braking force is created by the brake pad and brake disc. If one of the two are not in optimal condition, the actual braking potential cannot be achieved.
- ■ Brand new brake disc
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- ■ Brake discs that need replacement
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Brake disc in 'vinyl record' condition, with deep grooves.
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Brake disc with surface cracks.
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It is dangerous to drive with over-weared brake discs!
Have you ever thought, "Brake discs do not need to be changed because they are metal, and only the brake pads need replacement." or, "I don't drive on the race circuit and I drive safely on the street so I don't need it."
Have you ever taken a look at your brake discs?
Either disc surface appearance become LP record disc, or crack started, people think it is time to replace. In fact, brake disc surface worn smoothly, when outer area (edge) rose up time to replace.
Why do brake discs need replacement? The main reasons are 'friction heat', and 'heat capacity'.
What is braking?
When you step on a brake pedal, the brake pads and discs come to gather and causes friction.
By converting the friction energy to heat energy, the car is able to safely slow down.
This is how braking works. The 'friction heat' that occurs in the process is important.
Relation between Brake disc / pad
There is a "heat capacity" which brake disc / pad can store.
If new disc / pad heat capacity as "100", wear of disc / pad progress its heat capacity will be "90" → "80" →"70" ... and so on to reduce.
Then, heat not stored by brake disc / pad will transferred to caliper or brake fluid to create various heat damages.
Heat damages are
The following examples are typical heat damages
- Decrease of brake caliper rigidity
- Early worn disc / pad
- Distorted, crack, step worn on disc
- Brake fluid vapor lock, fluid leakage from screw
- Friction material separation by bending of brake pad back plate (backing plate)
To keep heat damage to minimum level, constant confirmation of disc / pad wear status is mostly important.
Further, we are marketing effective brake temperature indicator sticker detect heat damages.
When do brake discs need replacement?
For the front disc, when either side of the braking surface is worn more than 1mm. For the rear disc, when either side of the braking surface is worn by more than 0.5mm～0.75mm.
Wear limit value (Min. Thickness) is stamped on each disc as "MIN TH OO"
(Note, wear limit differ by part number and be cautious.
Incidentally our SD-disc front has slot shaved approx 0.75mm.
Therefore, when slot groove disappear it is a sign as replacement time.