![]() First find the correct caliper combination from the chart, then find the correct ratio for your master cylinder size. A balanced system includes the following things: 1) A lever that moves the entire stroke of the master cylinder 2) A Lever that moves comfortably in the confines of a car 3) Uses a reasonable amount of force to reach the desired system pressure 4) Is aligned well enough to minimize lever travelīelow is a calculator to help you find the correct ratios. Pedal force, system pressure and lever travel all need to be taken into account. The goal then is to balance the entire system. For instance, moving from a 3/4" master cylinder to a 1" requires 77.7% more force on the push rod. The result after adding the larger master cylinder is a harder pedal which needs much more pedal pressure to create the same amount of braking force. While a larger master cylinder will take up system slack with less pedal stroke, it will take more force to create the same system pressure. While a larger master cylinder creates a larger displacement, it takes more force to create the same pressure as a smaller bore. One of the most common misconceptions is that a larger master cylinder will create more pressure. ![]() Slack comes from two factors: retracted pistons must be moved back out, and misalignment caused by deflection in the axle and housing mis-alignment. Brake systems inherently have slack in the system that must be taken up before work can be done by the pads. If the desired pressure can not be easily attained the pedal ratio must be increased until the minimum pressure of 1000 psi is easily reached.Ī common problem in many applications is a spongy pedal. ![]() We recommend using a pressure gauge connected to the system to verify the maximum available pressure before running the car. A pedal ratio versus line pressure calculator is available below. With the correct master cylinder in place, the pedal ratio must be great enough to produce 1200 psi system pressure under severe braking conditions. Note that since AP doesn't provide any diagrams for the internal, patented workings of their cylinder, the implementation details could vary.Mounting the master cylinder to a frame rail or roll bar is recommended to ensure a solid mount. The secondary output is now directed to the brakes providing greater force. Once pressure increases, the changeover valve switches so that the output of the primary is directed to the reservoir and it moves freely. The primary output is directed to the brakes. When braking begins, the output of the secondary cylinder is vented back into the reservoir so it moves freely. The differential bore model looks very similar inside except the "primary" is larger than the "secondary", and both of the outputs are controlled by the external changeover valve. This provides hydraulic power for two circuits at the same time, like the front and rear brakes. Here we see two chambers that are compressed by two plungers that connect to the same rod. Lets compare this with a typical master cylinder from a passenger vehicle: Furthermore, if you continue reading their description, the primary chamber isn't activated again until the driver completely releases pressure on the pedal to prevent the switchover from happening rapidly (in the middle of a corner for instance). Once the secondary chamber is activated, the large chamber is not under any pressure at all. The smaller chamber provides a greater mechanical advantage, and the smaller amount of fluid is fine because the brakes are already tight. Once the pressure rises (as the brake pads contact the disk and tighten up), the external valve changes from the primary (large) chamber to the secondary (small) chamber. Initially when the large cylinder is active and high pressure is not needed, a larger amount of fluid is pushed into the system. In hydraulics, the difference in cylinder size is what gives you a mechanical advantage. The master cylinder has two chambers, and one has a larger diameter than the other. The small cylinder with the blue cap is the "external changeover valve". Looking at the picture of the "pull type" part might help:
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