The brake master cylinder is an essential element in any effective braking system, as well as essential for vehicle performance.
When selecting a brake master cylinder, there are various specifications to consider. These values will influence braking performance, sensitivity and power.
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Brake Line Pressure
By pressing down on the brake pedal, hydraulic pressure pushes against a piston inside of a master cylinder. This fluid then travels to slave cylinders at each wheel and fills them, forcing pistons to apply brakes.
Due to the larger ‘pushing’ area of slave pistons than that of a piston in the master cylinder, greater force can be exerted – this is why brakes are so effective.
Brake lines and hoses that carry hydraulic fluid to each of the four brakes must withstand a great deal of pressure, from several hundred pounds per square inch up to nearly 2,000 psi. These steel and rubber pipes are essential in keeping you safely on the road.
On vehicles without anti-lock brake systems, a rear brake line pressure-limiting valve is used to limit the amount of load transferred from the front to the rear. If this valve becomes tripped, it may take multiple attempts to un-trip it.
Brake Lever Travel
Brake lever travel refers to the distance cable ends must move from their exit point in the cable housing to contact with the lever pivot (Figure 2), depending on its design.
When pulling on a lever, there is often an imbalance between its pulling force and how far the cable travels. This is especially true for older cantilever brake levers which typically need more cable travel in order to apply enough pressure on the brake pads.
This issue can be corrected by adjusting the cable at the bridging hole so it never touches the brake linkage when operating the hand lever. If this is not done, the Travel Agent mechanism may jam and prevent further cable pull or braking action.
Brake Piston Travel
The brake piston travel of a CNC brake master cylinder is critical in how well your caliper works. Even piston travel can help minimize power loss, uneven pad wear, and make mounting your calipers much simpler.
Particularly with new calipers, which may not have had time to balance their pistons properly and lead to power loss or uneven brake pad wear.
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If your calipers are not balanced, try pushing both pistons back into their bores with either a plastic tyre lever or the ring end of a small spanner.
Carl Bush, a mechanic at HEL Performance, explains how to calculate this number. Essentially, you take the radius of the master cylinder (half an inch) and multiply it by its bore area.785″ squared for a 1″ bore. This gives you the exact braking stroke that the CNC master cylinder will generate with 100 pounds of force applied to it.
Brake Pedal Travel
Once you press the brake pedal, a CNC brake master cylinder generates hydraulic pressure to both front and rear brakes. This pressure creates friction material on brake pads (or calipers) and shoes, effectively stopping your wheels from rotating.
The brake pedal travel, or how far it moves from the top to the bottom when depressed, is another factor that can influence how your CNC brake master cylinder functions. This amount of travel depends on both the bore size of the master cylinder and your brake pedal ratio.
As a general guideline, the smaller the bore of your CNC brake master cylinder, the less brake fluid will be moved. Therefore, more pedal travel may be necessary to make up for any differences.
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