The brake master cylinder is responsible for distributing fluid from the reservoir to the front and rear brake systems. The fluid reservoir actually sits on top of the master cylinder with hard metal brake lines running out of it. There are a few places where the master cylinder can leak and cause a spongy or soft brake pedal. The inside has several pistons with o-rings and seals that can fail and allow brake fluid to escape. Likewise, the external metal lines also have o-rings where fluid can seep out or let air/moisture in.
If the brakes in your BMW have begun to feel a little soft or stopping doesn't seem like it used to, it may be your vacuum pump. The vacuum pump assists the power braking system in providing ample braking pressure.
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Technical Data Sheet: Rein Automotive OE Vacuum Control Valve Part Number: 11617521860 Engineering peak performance in European power units requires absolute fidelity to original equipment specifications. The Rein Automotive OE Quality Vacuum Valve is engineered to meet the rigorous demands of professional motorsport and high-performance maintenance environments.
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Most vehicles send engine vacuum from the intake manifold to the brake booster to provide power assistance to the braking system. However, due to your vehicle's engine having different vacuum characteristics, BMW decided to use an electronically operated auxiliary vacuum pump instead. Mounted to the front of the cylinder head, this part serves as the vacuum source and replaces the vacuum your brake booster would be receiving from the intake manifold. An auxiliary vacuum pump failure could cause many symptoms, most commonly a harder-feeling brake pedal resulting in longer stopping distances. A failure could also result in a vacuum leak, triggering a check engine light and potentially causing the engine to stall and run poorly. If your car exhibits any of the above symptoms, it may be time to replace your vacuum pump. Thankfully, this Febi replacement functions identically to the factory component.
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