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.
Found at the front of the cylinder head, this auxiliary pump sends vacuum to the brake booster to provide assistance to your braking system. A failure could lead to harder pedal feel and increased travel, as well as a vacuum leak.
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