Brake fluid is the lifeblood of your braking system. Periodic flushing about every 25,000 miles removes contaminants that can change clean fluid into brown mud.
Unless you own a power bleeder, brake flushing takes two people. First, open the hexagonal bleeder screws located at each caliper cylinder. Caution: Many older-model cars may have corroded hex screws which can seize. Lube the screw before attempting to loosen it.
After opening the screws have your assistant depress the brake pedal several times until no more fluid flows out. Close the screws then refill the system at the master cylinder. Cover the master cylinder, pumping the brakes several times.
At this point, bleed the brakes at the calipers and cylinder to remove air from the system. Crack the bleeder fittings on all four calipers or brake cylinders - but be careful. These bleeders tend to corrode, especially if the brakes haven't been bled regularly. Use penetrating oil, let it soak for a while, and employ a proper-sized box wrench to turn the bleeder. Then open one rear bleeder, and pump the master cylinder dry by stroking the brake pedal up and down repeatedly. Close the rear bleeder and pump the front dry as well.
Close the bleeder and top off the brake reservoir with fluid from a freshly opened can. Have a helper hold the brake pedal to the floor while you open and shut a rear bleeder. Do this repeatedly until you get mostly fresh, clean fluid instead of air. Repeat this for the other three wheels, and then do all four again but keep the reservoir at least half full.
Many restorers advocate using silicone brake fluid. The advantage of silicone is that it does not attract water into the braking system, greatly extending the life of brake seals and lines. On the down side, silicone is triple the cost of regular brake fluid. Additionally, silicone is to water what oil is to vinegar. Unabsorbed moisture can collect in low spots and rust out the hydraulics. Also, some silicones may not be compatible with regular glycol-based fluids, requiring a complete overhaul of the brake system to change over.
