[header] How to replace a master cylinder [title] Locate the various components of the vehicle's brake system. [substeps] Use your vehicle's manual to identify these components. Locate the brake fluid reservoir, the brake master cylinder, the brake fluid level sensor, and the brake fluid lines. 
The brake fluid reservoir is usually at the top of the brake system and contains brake fluid. It can be identified by the presence of a threaded cap on top of it.