In the low temperature season, a sharp abnormal noise occurs when braking at low speed. Why is this happening?

As the temperature decreases, the probability of abnormal brake noise will become higher and higher.

The degree of abnormal noise varies, but most vehicles will have obvious abnormal noise when braking at low speeds. The braking noise of some vehicles is more exaggerated than the whistle; this is the case for vehicles used by individuals, but the degree of different vehicles is very different.

Then we have to talk about the first reason. Reason 1: The brake discs and brake pads did not run in well.

Nowadays, cars basically don't need to be deliberately run-in, because the intention of the run-in is to make the engine and transmission run more smoothly, and at the current level of craftsmanship, there is no “metal burrs”; however, brake discs and brake pads still need to be run-in, because the manufacturing process standards of these two accessories are not very high, especially brake discs.Ordinary brake discs are made of gray cast iron, and they rust when they are stained with water. Such brake discs obviously do not have high standards; therefore, brand new brake discs do need to be run-in. The way to run-in is to brake normally and avoid braking sharply. Medium and low-speed transportation driving requires running-in for more than 500 kilometers, and running at high speed for two to three hundred kilometers.

If there is no ideal run-in, abnormal noise will occur due to uneven contact surfaces when braking at low speeds; the friction vibration frequency during high-speed braking is relatively special, and there will be no abnormal noise, but the vibration frequency at low speeds happens to meet the standard for abnormal noise, so it will be particularly obvious at low speeds.

However, the root cause of abnormal noise at low temperature still lies in temperature and braking strength. Too low temperature will change the performance of metal materials; it takes a long time to analyze from a professional point of view, and it is difficult to understand. Let's talk about it briefly here.Taking the brake disc as an example, low temperature will change the standard of plastic deformation of the brake disc material. The direct result is a change in the ability of the brake disc to absorb impact energy and deform; it can be understood that low temperature makes the brake disc hard and brittle. Under the conditions of the same braking strength, the degree of micro-deformation of the brake disc and brake pads changes, which will also cause abnormal noise.

When braking at high speed, a lot of heat energy will be generated due to friction, and the temperature of the brake discs and pads is relatively high, so the probability of abnormal noise will be relatively low; normal driving will rarely brake after starting, because it will always be driving on a smooth road; even if the brakes produce a slight abnormal noise during driving, it is not necessarily found, after all, the windows are always closed when driving in winter, and the wind noise and tire noise can mask the braking noise when driving at higher speeds.

Conversely, in low-speed driving, the temperature of the brake will be reduced due to air cooling, and the weakening of other noise will also make the braking noise more obvious.

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