What Causes Soft Brakes After Changing Brake Fluid?
2 Answers
The main reason for soft brakes after changing brake fluid is: errors during the replacement process caused air to enter the brake lines, which needs to be promptly purged. The method for bleeding brakes: 1. Two people are required to cooperate to avoid mistakes. 2. First, one person presses the brake pedal 4-5 times, while the other loosens the bleeder screw on the brake caliper. 3. If there is indeed air in the brake lines, some brake fluid and gas will spray out at this point. 4. Repeat the above steps. When only brake fluid sprays out, it indicates that all the air in the brake lines has been expelled. Finally, tighten the bleeder screw. 5. After this, the soft brake issue will be noticeably improved.
Last month after changing the brake fluid, I also encountered this situation - the pedal feel became spongy which was quite scary. The mechanic told me the most common cause is incomplete air bleeding, where tiny air bubbles remaining in the system will lengthen the brake pedal travel. Another possibility is using different specifications of brake fluid or mixing brands, which can alter the boiling point and affect pedal feel. It could also be that during the fluid change, aged hose connections were loosened, causing minor leaks. He advised me to return to the shop immediately for vacuum-assisted re-bleeding, especially emphasizing never to use the pedal-pumping bleeding method as it doesn't fully remove air. After redoing the procedure, it indeed returned to normal.
