The classic car brake master cylinder is a critical component to your car’s braking system. Understanding the role of the master cylinder can help you determine if you want to replace it and what to look for in a replacement or an upgrade for your classic car. Let us take a brief overview of a braking system, then get into detail about the role of the master cylinder. We will look at single and dual reservoir cylinders, bore size, and all the components of the master to help you make the best choice for your vehicle.
Whether you employ an all-disc system, a disc/drum combination, or an all-drum setup, the role of the master cylinder remains the same.
The act of braking begins when you depress the brake pedal. The car brake master cylinder uses that pressure to push a piston and send hydraulic fluid through the brake lines to each individual brake. Pistons inside of a bore that are located on each of the four brakes, fill with brake fluid and engage the pads or shoes and squeeze against the rotor or brake drum and stop your classic car.
Simply put, the mechanical pressure exerted on the brake pedal by your foot gets converted into hydraulic pressure by the car brake master cylinder. That pressure sends the fluid through your brake lines and engages the pistons at each of the four wheels, thus activating the brake calipers and slowing or stopping your vehicle.
Single vs. Dual Reservoir Master Cylinders
There are two types of master cylinders: single reservoir and dual reservoir. Single reservoir systems feed both the front and rear brakes from a single reservoir and brake line while dual reservoir systems have one reservoir feeding the front brakes while the second reservoir feeds the rear brakes through two separate brake lines.
The failsafe of the dual reservoir master cylinder ensures that, in the event of a malfunction, your chances of having some working brakes are better than they are with a single reservoir master.
Bore Size
In addition to the reservoirs, the function will be affected by bore size. Bore size can range from 7/8” to 1-1/4” and will affect pedal travel distance and effort. In other words, a smaller bore size will increase pressure and decrease the amount of effort required by you to stop your vehicle.
Decreasing master cylinder bore size will decrease your pedal effort and increase your pedal travel. Conversely, a larger bore in your car’s master cylinder will, with all other components being consistent, increase your pedal effort and decrease your pedal travel. As with some other brake parts purchases, this comes down to your preference for how the brakes “feel” underfoot when you are driving. Bore size is also especially important to consider when changing your car from drum brakes to disk brakes as the flow is a critical part in the brake operation.
Components of a Master Cylinder
Now that we know the two main types, let us delve into the main parts of the master and how it works to regulate your braking system.
Reservoirs
The reservoir, or reservoirs, are used to house the brake fluid. In a dual reservoir system, the reservoirs can be of equal size but in other master cylinders, one of the reservoirs might be smaller. No matter the size, one of the reservoirs feeds the front brakes, while the other reservoir feeds the rear brakes. it does matter which of the reservoirs is used to feed the front or rear and that is dependent on the actual master cylinder as there is not a standard.
Piston
Machined into the center of the master cylinder body is the actual bore of the master cylinder which houses the pistons. The pushrod from the brake pedal or the booster pushes against the piston housed inside this bore. When the pedal is pressed, the piston is moved inside the bore and pulls fluid from the reservoir and compresses that fluid thus creating hydraulic pressure to the rest of the system. The harder the pedal is pushed and the further the piston travels will create more line pressure.
Spring
The spring is a component inside the master cylinder bore that provides resistance when applying the brake pedal and allows the piston and brake pedal to return to their original position after the brakes are no longer engaged.
How Do You Know When the Master Cylinder Has Gone Bad?
There are internal and external seals inside the master cylinder. The breakdown of these seals over time results in brake fluid leaks outside of the unit or brake lines. Typically, if your master cylinder needs to be replaced, your brake pedal will feel mushy or spongy. In some cases, the brake pedal will even drop or fall to the floor when the vehicle comes to a complete stop.
Features to Consider
Many older classic cars have a single reservoir system so many consider changing to a dual reservoir master cylinder as a simple upgrade for safe braking. It depends on if you a going for an exact restoration or a driver quality classic car.
In addition to bore size, which is typically selected based on brake type, consider which side of the master cylinder would be ideal for port location when placing and installing the master. An adjustable pushrod attachment may work for your classic car as well.
A braking system’s master cylinder is a critical component that transfers the physical force into hydraulic force, sending brake fluid through the brake lines to engage the calipers and stop your vehicle. It is important to consider master cylinder size, port placement, and bore size when choosing the one that will fit your classic car the best.
