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 team 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.

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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.