What Causes Brakes to Sometimes Feel Soft and Sometimes Hard?
3 Answers
The reason is a malfunction in the vacuum booster pump. Below is relevant information about the vacuum booster pump: 1. Principle: The brake booster pump utilizes the principle of the engine drawing in air during operation, creating a vacuum on one side of the booster. This generates a pressure difference compared to the normal air pressure on the other side, which is used to enhance braking thrust. Even with a slight pressure difference across the diaphragm, the large surface area of the diaphragm can produce significant thrust to push the diaphragm toward the side with lower pressure. 2. Types: Camshaft-driven, engine-driven, and electric vacuum pump-driven.
I've been driving this car for over a decade, and I've noticed that changes in brake pedal firmness might indicate an issue with the hydraulic system. The most common cause is air bubbles or moisture in the brake fluid, causing fluctuating hydraulic pressure and inconsistent pedal feel. It could also be due to aging or leaking seals in the master cylinder, which wear out over time. Additionally, if the car frequently travels on rough roads, loose brake line connections might lead to instability. I recommend first checking if the brake fluid has turned dark or contains contaminants—replace it if necessary, don't wait until the problem worsens. Safety is paramount; never underestimate this issue—regret comes too late after an accident. Now, I make it a habit to maintain the brake system quarterly—spending a little saves both peace of mind and time.
From my past experience as a taxi driver, fluctuations in brake pedal firmness are no small matter. It's mostly caused by internal wear in the brake master cylinder or air leaking into the lines, which disrupts hydraulic pressure and leads to inconsistent pedal feel. It could also be related to the ABS system, such as when sensors detect abnormalities and automatically adjust pressure. Another possibility is low or contaminated brake fluid, making the system unstable. I usually do simple checks myself: after starting the car, pump the brakes a few times to see if pedal return is consistent. If not, I take it to a professional shop for hydraulic pressure and vacuum tests with proper equipment. Remember, such issues shouldn't be ignored—sudden brake firmness or softness at highway speeds is dangerous. Address it promptly for safety.
