Article - An Overview of a Brembo Master Cylinder

[oppracing]

An Overview of a Brembo Master Cylinder
Updated: August 28, 2008

(c) OPP, 2007

Upgrading your brake or clutch master cylinder (hereafter referred to as a "master") is a great way to improve the feel of your braking system. A Brembo master cylinder offers a wider choice of master cylinder configurations and better construction than a stock master. That's not to say that your stock master is crap but in most cases, it's like trading in your Lada for a Ferrari.
This article is an overview of a standard Brembo brake master cylinder and is written to help people with basic knowledge of brake systems understand this important yet often overlooked mechanism. One thing that OPP is really big on is educating our customers about our products - we want our customers to really understand what they are buying so they can get to most out of their new purchase.
OPP carries Brembo Brake Master Cylinders and Clutch Master Cylinders as well as the full line-up of Brembo products (ie. front calipers, rear calipers, rotors and High Performance kits).

A Simple Overview of the Radial Master Cylinder mechanism
In this overview, we will examine the different features of a lever and break it down. But before we start, let's figure out how a radial master works in a really simple diagram...

Ok, to sum up this diagram, you pull the lever towards you and it pushes a plunger through a cylinder. That plunger squeezes out brake fluid out of the cylinder, down your brake hoses and into your calipers. The brake fluid in the calipers push the brake pads into the rotors, causing them to grab onto the brake rotors, thus causing you to slow down or stop.
Hey, let's stop and take a look at this lever design - it'll explain why most aftermarket master are radial. Notice the direction of the plunger and the direction that the lever travels. With a radial master cylinder, the plunger travels in the same direction as the lever. In a "conventional" master cylinder, the plunger actually travels perpendicular (or pretty close to perpendicular) from the direction of the lever. It makes sense that you can get a better feel for the lever if it's going in the same direction as the piston and plunger (radial) rather than going off on some funky angle (conventional). This is the main advantage of the radial design.
Understanding the Features of a Brembo Master
Now that we have a basic understanding of a master cylinder, let's look at the important stuff to know about a Brembo master. We can figure out most of the important stuff by the name of the lever. As an example, we'll use a 19x16 Billet Non-Folding Radial Brake Master Cylinder...let's look at the picture below:

Excuse the clutter in the photo. Think of that as a metaphor for the complexity that one faces when customizing a brake system or an example of how bad I am with Photoshop.
Example: 19x16 Billet Non-Folding Radial Brake Master Cylinder
19x16: This specification indicates two values. The first value is the diameter (ie. bore) of the cylinder in millimeters - it is usually 16mm or 19mm. In this case, the diameter is 19mm. The second value is the inter-axis (ie. distance) between the lever's pivot point and the plunger that pushes into the cylinder - it is usually 16mm, 18mm or 20mm. In this case, it's 16mm.
Now that we know what the numbers are, let's figure out what they mean in terms of braking performance. When you are selecting a master, you need to understand that these values trade-off braking sensitivity and braking power.
For the cylinder diameter, as that value increases, you increase your braking power. As you increase the diameter, you increase your cylinder size and increase the volume of brake fluid that you have to compress. This creates a dampening effect that allows you to better modulate the amount of brake pressure. As a general rule of thumb, you would use a 16xXX for a single caliper set-up anda 19xXX for a dual caliper set-up. Of course, there are always exceptions - for example, the stock master cylinder for Yamaha R1's and R6's (which are made by Brembo) use a 16xXX set-up, despite the fact that they have dual front calipers.

For the inter-axis value, as that value increases (ie. the distance gets longer), you are decreasing your sensitivity and increasing your brake power. I don't want to get into the technical aspect or into the physics of it...that's not the goal of this article. If you feel like you need to know more, I would recommend you search Google or How Stuff Works. In a general comparison between a 19x18 and 19x20 configuration (the most common configurations for sportbikes), a 19x18 has more feel but has a little more lever travel than the 19x20. A 19x20 configuration has more braking power and requires less distance to completely pull in the lever.

Ultimately, the optimal configuration is up to you. Brembo recommends the 19x18 configuration for racers and the 19x20 configuration for street riders. In terms of real world examples, the billet master cylinder using in MotoGP is a 19x18 while the master cylinder includes with the Brembo High Performance street kits is a 19x20.
Billet: Master cylinders are manufactured using two processes and are designated as either billet or forged. A billet master is cut from a solid block of aluminum using a CNC machine. This machine is computer-controlled and can carve out masters to very precise tolerances. A billet master is very precise but also very expensive to manufacture. A forged master created by heating a blob of aluminum (known as an ingot) to a temperature where it is malleable (but not a liquid) and pressing it into a mould to form the final shape. (It's different from casting where the metal is heated into a liquid state and poured into a mould.) The forging process is relatively crude and may have imperfections such as air bubbles or rough surfaces. A forged master is not as precise or refined as a billet master but is much cheaper to manufacture.
Non-Folding: Brembo masters are designed to absorb crash damage in one of two ways. The first method is through a folding lever. This lever has a hinge in it which allows the lever to swing up or down in the even that the motorcycle gets dumped. The second method is through a cut in the end of the (non-folding) lever. This is a deliberate weakness in the lever design - the lever breaks at the cut and absorbs energy. Sure, you end up with a broken lever but at least you still have part of a lever so you can use it to ride home. If you look at footpegs for rear sets, you may see the same idea at work. Breaking a lever is an easy replacement. Breaking the master cylinder means you have to replace the whole thing...not too good if you've invested in a Brembo.
To illustrate the differences, check out the picture below:

Radial: We discussed this a little bit at the start of the article. All of the master cylinders available from Brembo are radial masters so this is just a friendly reminder that you are purchasing a master cylinder with an improved design.
Brake: A master cylinder is not restricted to just the brake side! Some bikes such as the Honda CBR1000RR 2004-2005 or the venerable Suzuki Hayabusa feature hydraulic clutch systems. Rather than using a cable system, the clutch is activated through a fluid mechanism that works under the same principles as the brake system. A cable system is still considered to be a better system but converting from a hydraulic clutch to a cable clutch is an expensive and time-intensive project. It's easier to improve the system by replacing the master instead.
Final Words
Well, that's all that I have to share about Brembo master cylinders. I hope you've gained a greater understanding and appreciation for the function of this part. I would like to really stress the importance of the brake system - with all of the hype surrounding maximum horsepower, you gotta remember that you have to be able to stop too!!! I hope to be able to travel other brake components such as calipers, brake pads, rotors and brake lines down the road.
If you have any comments, feel free to email me at info@oppracing.com.
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