Need help with master cylinder theory/operation, please.

[priobe]

Dugly,

Ok, hmmmmm.... I have just gone through a full brake system inspection, redesign, and implementation. I was able to gain the results I was looking for with a lot of help from some people on CC, and the Internet.

First of all Pedal ratio
The statement that a larger pedal ratio for manual brakes is true, however what I have found is that manual brake pedal ratio actually starts at 5:1 ratio. Yes, it is true the small the pedal ratio the more pressure will need to be applied to stop the vehicle, compared to a larger pedal ratio. As mention in this thread a 6:1 ratio is ideal. In any spread sheet I have seen to determine the master cylinder size the applied pressure rating is always to determine lockup pressure of the tires. So keep in mind if you really want to lockup the tires you have to be realistic with the pressure. I would recommend about 150 lbs + / -.

You MUST determine that the push rod travels completely straight with a + / - 2 degree variance. Indication of the leaking on the firewall maybe a sign that the push rod is not traveling with full stroke completely straight.

Calipers

In order to make a educated suggestion, we will need to know caliper piston size of the calipers. By indicating that the calipers for front and rear are the same may not be true. A lot of Wilwood calipers can be ordered with different piston configuration. As an example the same calipers can carry a 1.75 piston or a 1.38 piston in the same physical bodied unit.

Furthermore, these calipers vary for rotor size thickness which will help in heat dissipation. The further you can put your caliper away from the center or the rotor the easier it will be to slow down the rotating mass, due to it spinning slower.

Line Pressure

Recommend brake lines should be 3/16 and hard lines should be used where ever they can be used. Areas that require movement such as body to chassis or chassis to caliper should have a good quality braided brake hose.

Wilwood calipers are rated at 1200 psi before deflection occurs. Manual brake pressure are typically around 600 - 1000 psi. SSBC suggests brake pressures to be between 600 - 800 psi, I think anything lower than 600 psi for the front and dont even drive the car.

You can find these pressure gauges in the popular online shops. I would recommend getting 2 to 3 gauges. 1 for the front 1 for the rear and the 3rd (optional) for the master cylinder. The 3rd pressure gauge will help show the variance from the mc change to the calipers. Don’t confuse this pressure with clamping force, which is much greater.

Dual Master Cylinders VS Tandem

By going with a dual MC you will be able to configure / tailor your brake system to you liking easier. This is mainly because you have a larger variety or cylinders to choose from and mix and matching front to rear selections. Keep in mind the amount of pressure being applied to the dual setup is divided in ½. So, if a dual system receives a applied pressure of 150 lbs. this pressure is divide amongs 2 cylinders delivering 75 lbs each. A balance bar will help distribute this applied pressure (150 lbs) evenly or unevenly to either your front or rear. A proportioning valve is installed on the rear reducing the pressure to the rear braking system.

A tandem system will receive a full amount of pressure applied through a single push rod. Keep in mind this system is less tunable with the limited sizes that can be applied.

In conclusion, you will find many examples of dual MC’s with a selected value but good luck finding all the variations in a braking system for you to create a cookie cutter system to apply to your situation. My suggestions and to save time and money would be to make sure you do your homework on this. You do not want to take the cheap route with your brakes. I have adapted a Wilwood pedal system (hanging mount) 6.25:1 to my application. I initially thought the system would not fit in my foot box but until I fit and tested the system it worked very, very well. Additionally, keep in mind by increasing you clamping force in the rear this in turn reduces the amount of effort needed (to a certain extent) to the front. Typical balance for front to rear is a 70 /30 (front /rear).

The knowledge I have obtain and suggest in thread is what I have gathered, tested with working results on my own vehicle.

This is just a small percentage of information that I have gathered and share, a lot more information is definitely needed. I hope this help you and others, braking should be taken seriously.