Correct Selection, Replacement and Replenishment of Brake Fluid in ABS System (Part 1)

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Correct Selection, Replacement and Replenishment of Brake Fluid in ABS System (Part 1) [Copy link]

1. Correct Selection

Since the ABS system is more complex than the conventional brake system, special attention should be paid to the following when selecting, replacing and replenishing the brake fluid:

(1) In the ABS system, the brake fluid has a longer and more tortuous path, which results in greater resistance to the flow of the brake fluid; in addition, in the ABS system, there are more and more precise moving parts, which also require higher lubrication. Therefore, the brake fluid selected for the ABS system must have an appropriate viscosity.

(2) In the ABS system, the brake fluid repeatedly undergoes cycles of pressure increase and decrease. Therefore, the operating temperature and pressure of the brake fluid are higher than those of the brake fluid in the conventional brake system. This requires the brake fluid to have stronger antioxidant properties to prevent the formation of colloids, sediments and corrosive substances in the brake fluid.

(3) In the ABS system, there are more rubber seals and rubber hoses. This requires that the brake fluid used by the user should not have a strong swelling effect on the rubber seals.

(4) In the ABS system, there are more and more precise metal parts. Therefore, the selected brake fluid is required to have better corrosion resistance to prevent rust on the metal parts.

(5) In the ABS system, there are longer and more complex pipelines. Therefore, the selected brake fluid is required to have a higher boiling point to prevent the brake fluid from vaporizing and causing air blockage in the brake system.

Based on the above characteristics, the ABS system generally uses DOT4 brake fluid. Although DOT5 brake fluid has a higher boiling point, since DOT5 is a silicon-based brake fluid, it will cause strong damage to rubber parts. Therefore, DOT5 brake fluid is generally not used in the ABS system. However, since DOT3 and DOT4 are alcohol-based brake fluids with strong hygroscopicity, the water content in them will continue to increase with the extension of usage time. When the brake fluid contains more water, it will cause the precision parts in the brake pressure regulating device to rust. In cold climate conditions, it will also increase the viscosity of the brake fluid, affecting the flow of the brake fluid in the brake system, making the brake slow and resulting in a longer braking distance. In addition, the water content in the brake fluid will have a very obvious effect on the boiling point of the brake fluid, causing air blockage. Generally, the water content of DOT3 and DOT4 brake fluid is 2% after 12 months of use. After 18 months of use, the water content can reach 3% on average. Therefore, it is recommended that you replace the brake fluid every 12 months.

2. Replacement and Replenishment

When replacing or replenishing the brake fluid in an ABS system with hydraulic power or power assistance, the following procedures should be followed:

(1) First add new brake fluid to the maximum level mark in the reservoir.

(2) If it is necessary to remove air from the ABS system, the air should be removed according to the prescribed procedures.

(3) With the ignition switch in the ignition position, repeatedly press and release the brake pedal until the electric pump starts to operate.

(4) After the electric pump stops operating, check the fluid level in the reservoir.

(5) If the brake fluid level in the reservoir is above the maximum level mark, do not drain the excess brake fluid first, but repeat steps (3) and (4) above.