The master cylinder is a system that hasn't changed much in its design for 80 years. Just like on a '49 Ford®, when you step on the brake pedal, a pushrod through the firewall actuates a piston in the master cylinder. The fluid pressure from this piston then travels through the hydraulic fluid in your brake lines and moves the pistons in each wheel cylinder, which then moves the brake pads or shoes.

If there's one sure-fire sign that your brake master cylinder is failing, it's this: while holding the vehicle stopped and in gear, the brake pedal slowly goes to the floor. If your master cylinder is starting to go, you can either rebuild it or just go with a new unit. You can even go with a sharp-looking chrome master cylinder to dress up your hot rod's engine compartment. Replacing the unit is fairly easy, as it's mounted within easy access on the firewall. Just remember, since the system has been opened while installing, you will need to bench bleed any air from the master cylinder itself and then thoroughly bleed air bubbles from all brake lines.