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Why does the fluid level decrease when brake fluid is not depleted?

Source:

Wondee Autoparts


In the routine inspection of vehicles, the inspection of various fluid levels is a relatively important item, and the inspection of brake fluid levels is of utmost importance because the brake system involves driving safety issues. We all know that the various components in the brake system do not consume brake fluid, and brake fluid does not evaporate. shouldn't the liquid level remain unchanged after being filled to a sufficient level? Why do we have to check every time? Why does the liquid level sometimes decrease?

In the routine inspection of vehicles, the inspection of various fluid levels is a relatively important item, and the inspection of brake fluid levels is of utmost importance because the brake system involves driving safety issues. We all know that the various components in the brake system do not consume brake fluid, and brake fluid does not evaporate. shouldn't the liquid level remain unchanged after being filled to a sufficient level? Why do we have to check every time? Why does the liquid level sometimes decrease?

brake fluid (1)

Under normal circumstances, the level of brake fluid does not change much unless there is a leak in the brake oil pipeline. The regular inspection of the brake fluid level is also to determine whether there is any leakage and eliminate hidden dangers. If the brake fluid suddenly becomes too low, much lower than the lower limit, then there must be a leak, so don't drive easily at this time. It is necessary to check and determine the cause of the low brake fluid, identify the leakage point, and repair it before continuing to use the vehicle.

brake fluid (2)

There is also a situation where the lack of brake fluid is caused by thin brake pads, which can sometimes occur. The handbrake light of a car is constantly on, and even when the handbrake is put down, it does not turn off. After inspection, it was found that it was caused by a lack of brake fluid. Continuing to check the cause of the brake fluid shortage, it was found that there were no leakage points, only the brake pads were thin. Why does the brake fluid level decrease when the brake pads are thin? This is because the brake pads and brake discs are always close together. When the brake pads are worn thin, the piston of the slave cylinder must move outward so that the brake pads can come into contact with the brake disc. When the piston moves outward, there is a space behind it that needs to be filled with brake fluid. Part of the brake fluid in the oil pot enters this space, and its liquid level will inevitably decrease.

brake fluid (3)

If there is not much brake fluid added when a new brake pad is installed, the brake pad will become thinner and the fluid level will be lower than the lower limit. Just replace the brake pads to solve the problem. If the brake pads have not worn to their limit yet, just add brake fluid. Please note that excessive brake fluid should not be added at this time, as long as it is slightly above the lower limit. Because if too much is added at this time, when replacing the brake pads, the piston of the slave cylinder needs to be fully retracted, and the brake oil level in the oil tank will rise, even overflow, and flow to the engine and transmission. Brake oil has strong corrosiveness, and once it flows onto rubber parts or circuits, it will corrode them and accelerate aging. Sometimes when encountering brake fluid overflow when changing brake pads, this is the result of adding too much brake fluid before.

brake fluid (4)

Therefore, if it is found that the brake fluid is insufficient, the first step is to check whether the brake pads are worn to their limit, and then check for any leaks. In reality, there are very few faults with brake fluid leaks. Many manual transmission cars share the same oil tank for clutch oil and brake oil, and clutch oil is brake oil. So if there is no leakage in the brake pipeline and it is a manual transmission car, it is also necessary to check whether the master cylinder and slave cylinder of the clutch are leaking oil, as their leakage can also cause a decrease in brake oil. Of course, if there is a separate oil tank for the clutch oil, there is no need to check it.

 

From: WONDEE Autoparts 2023-12-29

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