Videos & Galleries

Video: How Master Cylinder Bore Size Affects Braking

Learn the basics of how your master cylinder bore size affects braking performance and pedal feel by watching this four-minute Summit Racing Quick Flicks video.

The boys at Summit Racing will try not to bore you.

 

Welcome back to Summit Racing Quick flicks, today we are going to address some frequently asked questions about master cylinder bore sizing so prepare to be bored.

 …

In our previous videos about braking system components, as far as master cylinders and disc brake versus drum brakes go, we addressed some generalities as far as what master cylinders are right for an application. The thing about it is, that is one of those things where you really have to do your research to determine which one is going to be correct if you are building a custom system because there is a lot of different ranges of master cylinders out there that are available.

The main factor that is going to come into play is the bore sizing of the master cylinder which I think most people have a little bit of confusion about as far as what is right for what type of system. In reality you’re going to come to find that bore size is critical to how that brake system is going to function and it has a lot to do with pressure as well as capacity. Logic would tell you that a larger bore size in a master cylinder should produce more pressure but that is actually not true. Because of fluid velocity and fluid movement in most cases the smaller the bore of the master cylinder means the more pressure you are going to have at the caliper assembly or the wheel cylinder assembly. Whereas if you have a larger bore master cylinder it is actually going to produce less pressure, its actually going to give you a harder pedal feel as an end result.

Having a general understanding of bore size is critical to selecting the proper master cylinder for your application. Getting the right master cylinder is all about proper pressure whether it be at the caliper or at the wheel cylinder. Generally speaking we want the pressure at the caliper to be somewhere between 900 and 1,200 psi, question is how do you know if that master cylinder is going to make that pressure at that caliper assembly. The thing about it is, you won’t know. It is kind of one of those things that become a guessing game in the end to determine which one is going to be right. With the right amount of pedal pressure you will almost always be able to get there the thing about it is what kind of pedal fill do you really want from that vehicle and how do you really want the brakes to respond.

Some prime examples of figuring out which way you need to go with the master cylinder is let’s say you put a master cylinder on and the pedal pressure seems pretty extreme. It’s got a hard pedal, that usually is an indication that bore cylinder or the piston size of that master cylinder is too large, meaning that it’s not creating enough pressure at the caliper assembly to go ahead and give you that loose pedal feel that you want. But good braking the opposite can kind of be true where you have an extremely soft pedal where the brakes are real grabby. That can actually mean that the bore size is too small and you are building too much pressure too quickly therefore you have to go up in size as far as the bore size of the master cylinder. Supplying information on which master cylinder is exactly right for your application is really not possible for us to do via a video. Every application is completely different from the next and will have specific needs. So if you need more information or more help on selecting which master cylinder is right for your application please contact our tech department at 330-360-0240. 

 

 

 

Tags: , , ,

5 Comments

  1. Surely volume required by the slave has to be equated to volume the master can supply. Pressure is a function of foot pressure and servo pressure!

  2. I have a 1973 camaro, disc front drum rear. The standard replacement master cylinder from Auto Zone / Advance shows a bore of 1.125,. However, I do see master cylinders at Summit with bores of 1 inch. Our foot pressure is moderate + to stop the car with a 1.25 bore. Would going to a 1 inch bore create any issues?

  3. Bud Walters says:

    TO have the same braking result, you will need to move the brake pedal 1.266x the distance
    (to get the same fluid volume) and exert .789 times the pressure applied–less pedal pressure for the same fluid pressure.you will have to check the pedal travel to see if it is feasible–if there is enuf room to push it further–some push rods have eccentric adjusters to set the pedal height

    if it has power assist ,it may feel spongier.,but less pedal pressure may be a good thing if you dont mind the travel

  4. So what size master cilinder would I need for a 1966 c50

  5. Hi, Thanks for the article. I have a 1976 cj7 jeep that I converted from manual front drum brakes to power front disc brakes and am using a brake booster assembly, mc and PV off a YJ jeep wrangler but have a really soft pedal. I have to pump the brakes to get it to stop and the pedal almost hits the floor before I feel it grab. The booster rod to the pedal was a bit longer than my original manual brake pedal rod.. So I lowered the pedal to line up with the rod.

    Any idea what could be causing the excessive soft pedal? Any ideas?
    I do get vacuum at the booster.

    But if I pump the brakes the engine idle goes up a little. Not sure if that is normal?

    Thanks for your help!

Leave a Reply

Your email address will not be published. Required fields are marked *

*

This site uses Akismet to reduce spam. Learn how your comment data is processed.