What is the fault when the BMW 5 Series has hard brakes and no power assistance?
3 Answers
The cause of the fault is air leakage or failure of the vacuum booster pump. The following is an introduction to the brake booster pump: 1. Principle: During the braking process, the vacuum entering the booster pump is controlled to move the diaphragm, and through the linkage device, the push rod on the diaphragm is used to assist human force in stepping on and pushing the brake pedal, thereby amplifying the force exerted by the driver on the pedal. 2. Function: Utilizing the principle of air intake during engine operation, a vacuum is created on one side of the booster pump, forming a pressure difference relative to the normal air pressure on the other side. This pressure difference is used to enhance the braking thrust.
I also experienced extremely stiff brakes with no power assist when driving my old BMW 5 Series last time, which felt very dangerous—I almost couldn't stop at a red light. This is usually caused by a problem with the vacuum booster, such as a ruptured diaphragm or a leak in the vacuum line, preventing the generation of assistive force. The braking system of the BMW 5 Series relies on engine-generated vacuum for power assist, so if that fails, the brakes become very heavy. It could also be due to an aging vacuum pump or a clogged filter, but don’t attempt DIY repairs to avoid causing more issues. I recommend pulling over immediately, turning on the hazard lights, and towing it to a dealership or professional repair shop for inspection—they can quickly diagnose the issue with specialized tools. Regular maintenance should include checking the brake system, such as inspecting hoses for cracks, to prevent such failures and ensure safer driving.
As a long-time BMW 5 Series enthusiast, I believe the most common cause of hard braking without power assist is a failed vacuum booster. This component utilizes engine vacuum to aid braking. If the diaphragm is damaged or there's minor air leakage in the lines, insufficient vacuum will make the brake pedal extremely stiff and difficult to depress. Other potential causes include insufficient brake fluid, a blocked master cylinder, or ABS module failure, but booster issues occur most frequently. BMW's vacuum systems are relatively sensitive and prone to aging problems, such as seal degradation after prolonged use. Check for loose or cracked vacuum lines - a simple visual inspection can give you an idea, but don't attempt repairs casually since the braking system affects safety. It's best to have a thorough inspection at a reputable shop rather than cutting corners. Develop pre-driving inspection habits, like listening for weakened power assist sounds during engine startup, which helps detect potential issues early.
