Why does the brake feel soft after replacing the brake fluid?

[Harrison]

After replacing the brake fluid, the brake feeling soft is due to the poor performance of the brake fluid, which results in insufficient friction between the brake pads and the brake discs. Over time, moisture can seep in, and after the moisture evaporates, a certain amount of air gap is created between the brake pads and the brake discs, leading to the phenomenon of the brake feeling soft and ineffective. During normal driving, if the braking force fluctuates between light and heavy, the brake fluid should be replaced promptly. Before replacement, clean the brake system with alcohol. Do not mix different types or brands of brake fluid, as their formulations differ, and mixing can cause a decline in the performance indicators of the brake fluid.

[VonAnastasia]

I've encountered this situation before. After changing the brake fluid, the pedal feel became noticeably softer, mainly because air entered the system during the replacement process. Brake fluid is an incompressible liquid, but air can be compressed. When mixed in the brake lines, it makes the brake pedal travel longer, resulting in a spongy feel. At that time, I solved it by redoing the bleeding procedure: I had a friend repeatedly pump the brakes in the car while I alternately bled the fluid from the bleed valves at all four brake calipers until the fluid came out bubble-free. Remember to use the correct specification of new brake fluid, as mixing different DOT standards may corrode the seals. If you're unsure about doing it yourself, it's best to have a professional handle it, since brakes are critical for driving safety.

[LolaLynn]

I've experienced the issue of brakes feeling spongy after a brake fluid change firsthand last month at the repair shop. The mechanic told me it's mostly caused by incomplete air bleeding, leaving air bubbles trapped in the hydraulic system. The principle is simple: air is compressible while fluid isn't, making the brake pedal feel mushy. They also mentioned other possibilities like minor leaks at hose connections or master cylinder seal failure, though these are less common. I requested a re-bleeding procedure - they started from the right rear wheel and systematically bled each corner, restoring normal pedal feel in about twenty minutes. My advice: never rush off after a brake fluid change; always test the pedal feel by pumping it several times before leaving the shop.

[StElizabeth]

I've encountered similar cases several times when repairing cars. The main reason for the brakes becoming soft after changing the brake fluid is still air entering the system. The brake system must be completely sealed. If the operation is slightly improper during replacement, air will get in. The solution requires using professional equipment for secondary bleeding. Some car models even need to activate the ABS pump with a diagnostic computer to completely remove the air. Also, a reminder: never mix different types of brake fluid. Mixing DOT3 and DOT4 will lower the boiling point, creating vapor lock while driving, which is even more dangerous. If you're doing it yourself, remember to wear gloves throughout the process—this fluid is highly corrosive.