What Causes the Brake to Suddenly Become Hard and Unpressable While Driving?

1 Answers
SabrinaFitz
07/30/25 6:22am
When the brake suddenly becomes hard and unpressable while driving, it is related to a malfunction in the vacuum booster pump. Below are the reasons and solutions for the brake becoming hard: 1. Vacuum Booster Pump Air Leak: Under normal driving conditions, the negative pressure in the intake manifold draws air from the vacuum booster pump, keeping the pump in a constant state of energy storage. If the brake becomes hard upon the first press, it indicates an air leak in the vacuum booster pump. Solution: Replace the vacuum hose. 2. Speed Too Low, Gear Too High: Under normal driving conditions, the negative pressure in the intake manifold draws air from the vacuum booster pump, keeping the pump in a constant state of energy storage. If the brake becomes hard only after pressing it once, it might be due to insufficient intake negative pressure caused by low speed and high gear. Solution: Increase speed. 3. Leak in the Connecting Hose: A leak in the hose can lead to excessively low vacuum, causing the loss of power assistance and resulting in a hard brake. Solution: Inspect the vacuum hose to ensure it is sealed properly, restoring normal function.
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