Jim Smart
August 7, 2007

On vehicles built prior to 1967, a single-reservoir master cylinder applied pressure to all four brakes. From 1967-up, it became federally mandated to have a dual-braking system-with a two-reservoir, separated-bore master cylinder that divides front and rear braking systems. A dual-braking system enables you to have some braking pressure should one of the systems fail.

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Braking systems rarely complain, considering what we ask of them. Did you know you're supposed to flush and bleed your brake system every one to two years? Doing so removes all air and moisture from the system. Air gives you a spongy pedal. Moisture boils during hard braking, creating air pockets, pedal hammering, and ineffective braking. Fluid cannot be compressed, which is why it is effective for hydraulics. A spongy pedal happens because air can be compressed. Solid brake fluid makes a pedal hard because fluid cannot be compressed. A hard pedal means solid fluid cohesion (contact) between your foot and all four brakes.

Air and moisture get into brake-system hydraulics through steel lines, master-cylinder castings, and reinforced rubber hoses because all of these components are porous. They soak up air and moisture from the atmosphere. If you live in a damp location, the problem becomes even worse. This is why regular, preventative brake maintenance is so important.

When moisture and air collect in brake lines, the result is corrosion, pitting, and eventually, line failure. Old, pitted brake lines must be replaced. You can fabricate them yourself with proper tools and procedure, or you can order a set of CNC-manufactured brake lines and parts. Classic Tube offers bolt-on kits, or if you have a Ford or Mercury that isn't mainstream, the company will take your existing brake lines and custom fabricate a set from your lines. The choice is yours.

Drum-brake function is easy to understand. The wheel cylinder is a simple, two-way hydraulic actuator that pushes linings outward to contact and stop the rotating drum.

Brake Fluid
There are two basic types of brake fluid: mineral-based (DOT 3 and 4) and silicone (DOT 5). Mineral-based fluids seem to perform best because they help maintain a hard pedal. The downsides to mineral-based fluids are moisture absorption, contamination, and paint damage if spilled. Even the tiniest drop of mineral-based fluid will lift paint.

Synthetic, mineral-based brake fluid is DOT 4 spec, which can some- times give the impression it is unique. However, synthetic, mineral-based brake fluid is more resistant to moisture and other contaminates. It also has a higher boiling point, which makes it more effective during hard braking.Silicone brake fluid doesn't absorb moisture. It stands up to the punishment of hard braking because it has a much higher boiling point.

Silicone brake fluid doesn't damage paint either. However, it is slippery, nasty stuff. It also yields a spongy pedal with even the best bleeding procedures. Silicone brake fluid takes getting used to because the pedal is spongy compared to mineral brake fluid. If you're going to change over to silicone brake fluid, it is best to begin with all-new components and seals.

Synthetic, mineral-based brake fluid (DOT 4) can be mixed with mineral (DOT 3) fluids without consequence. We suggest going to synthetic DOT 4 brake fluid when flushing and bleeding the brake system.

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