How do I choose a brake master cylinder bore size?

Typically, a master cylinder has approximately 1-1/2-inch to 1-3/4-inch of stroke (travel). What you have to do is coordinate the pedal ratio with the bore size to arrive at approximately half of the stroke (roughly 1-inch) in order to make the brakes feel comfortable and stop the car safely.

How do you measure a brake master cylinder?

To get to this number you use the formula for Area which is: Area = 3.14 (Pi) multiplied by the radius squared. So you calculate the radius of 1” bore which is simply half of the diameter which equals . 5” (half an inch). The result is that a 1” master cylinder has a radius of half an inch.

What tools should be used to measure master cylinder piston to cylinder clearance?

Specific tools are required to measure piston to bore clearance. The list includes the following: micrometer, dial caliper, and bore gauge. Micrometers have a one-inch range and will be used to measure the piston. Select a micrometer with a range that includes the piston diameter.

Does the master cylinder affect the brakes?

A problem with the brake master cylinder will cause the brake pedal to behave abnormally. All the pressure in the braking system is generated from the master cylinder. If it malfunctions, the cylinder will not distribute pressure properly, and the pedal will be affected.

What should I look for when choosing a master cylinder?

There are some things you must know when selecting a master cylinder. A larger-diameter master cylinder will displace more fluid volume than a smaller-diameter unit, but will create less line pressure. The result is a harder pedal requiring more braking effort.

What are the recommended pedal ratios for a master cylinder?

Selecting the correct master cylinder is important and its requirements are linked to pedal ratio. The recommended pedal ratios are based on 150 pounds maximum force on the lever to attain the maximum rated pressure for the master cylinder.

What size master cylinder do I need for a disc brake?

If you’re changing a drum brake setup to disc, you’ll need a master cylinder with a larger bore diameter. In many cases, a drum brake setup will feature a 10-lb. residual valve at the outlet to maintain a slight residual pressure on the drum brakes.

What happens if the bore size of the master cylinder is decreased?

If the bore size of the master cylinder is decreased and the mechanical advantage (pedal ratio) and push on the pedal remain the same, the fluid pressure (PSI) and the stroke both increase. For example, a 100 pound push on the pedal and 4:1 mechanical advantage (pedal ratio) gives a 400 pound push on the master