What is the reason for the brakes becoming soft a few days after bleeding?
2 Answers
The reasons for the brakes becoming soft a few days after bleeding are as follows: 1. Brake fluid has not been replaced for a long time: If the brake fluid is not replaced in time, it will contain excessive impurities and moisture, which will affect the transmission of braking force. Therefore, the brake fluid needs to be replaced regularly. At the same time, car owners with the means can have the moisture content of the brake fluid tested at a professional repair shop. 2. Oil leakage or overly soft brake material: Generally, oil leakage from the brake master cylinder or brake lines will cause the vehicle's brakes to become soft. If the brake material is too soft, its high-temperature stability will deteriorate, which can also cause the vehicle's brakes to become soft. 3. Air in the brake lines: Brake fluid is the medium for transmitting force in the braking system. If air enters the lines, the brake fluid under high pressure will appear insufficient in strength, leading to a noticeable weakening of braking force. Therefore, it is necessary to promptly bleed the braking system.
Just bled the brakes and they felt firm, but a few days later they're spongy like stepping on cotton? I've heard many car owners complain about this. The most likely cause is incomplete bleeding initially, with air bubbles still trapped in the nooks and crannies of the lines—these bubbles compress like springs, causing a soft pedal feel. Additionally, for older cars, pay special attention to the master cylinder's seals; worn rubber cups can secretly leak brake fluid back to the reservoir. I once repaired a decade-old Tiida where internal master cylinder leaks had the owner coming back for bleeding every few days. If the brake line fittings are leaking, they can also draw in moisture, which evaporates and forms new air bubbles. After bleeding, firmly pump the brakes five or six times to test for changes in pedal firmness—if it still feels soft, redo the job immediately.
