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Master Cylinder

Q:   What master cylinder bore size do I need?

A:  The master cylinder bore size that you need is dependent on several variables. Choosing a master cylinder bore size begins with defining how the master cylinder will be actuated, manually or with the assistance of a booster, either hydraulic or vacuum operated. Once you have decided on how the master cylinder will be actuated, the information below can be used as a guideline for selecting the right master cylinder. Keep in mind that auto manufacturers have put many years of experience and a lot of testing into determining the right combination for a given car. When building a custom car with changes to the suspension, brakes, tires, and weight balance; you too may need to do some testing to determine which master cylinder is right for your vehicle.

The combined piston area and piston volume of your calipers and the pedal ratio, are two of the primary considerations. Whether the system is boosted or not is another consideration. Remember that a larger master cylinder bore produces more volume and a smaller master cylinder bore produces more pressure. To determine the appropriate master cylinder bore for your specific application, review Wilwood's Tech Tip Guide. You can also contact a Wilwood Sales Technician at 805-388-1188 or email Sales/Tech Support.

Q:   What master cylinder is best suited for my application?

A:  The goal is to select a master cylinder system that supplies sufficient fluid volume to provide a firm, responsive pedal, while generating enough pressure to stop the car comfortably. There are two types of master cylinders, single reservoir, single outlet master cylinders and dual reservoir, dual outlet (tandem) master cylinders. A tandem master cylinder will have two fluid output ports, one for the front brakes and one for the rear. A single fluid output master cylinder, or "fruitjar," will be plumbed to all four calipers as a single system.

Dual master cylinder pedal systems are used extensively in racecars and have completely separate master cylinder systems for the front and rear brakes. This setup permits easy adjustment of front to rear brake bias with the integrated balance bar assembly.

To determine the appropriate master cylinder and hydra-mechanical combination, review Wilwood's Tech Tip Guide. You can also contact a Wilwood Sales Technician at 805-388-1188 or email Sales/Tech Support.

Q:   How do I bench bleed my master cylinder?

A:  Place your master cylinder in a vise, holding it by the mounting bracket and making sure it is level. Thread one each “3/8-24 barbed fitting” into each of the pressure ports, then attach a six-inch piece of clear plastic hose to each barb. Fill the reservoir with new brake fluid; then place the other end of each hose into the reservoir, one on each side of the wall separating the two chambers. The hoses must remain submerged in brake fluid until the bleeding process is completed. Using full strokes, slowly push the piston in using a Phillips head screwdriver or other device that simulates a pushrod. Do this until ALL of the air bubbles have disappeared from the clear plastic hose.

Q:   I put your front and rear kits on my vehicle, but the pedal goes to the floor? What is causing this to happen?

A:  If the brake system has just been filled up with fluid for the first time, and you are having trouble getting a pedal, refer to the master cylinder and system bleeding procedures within this Frequently Asked Questions section. There are several other possible causes, beginning with a sudden fluid loss due to a master cylinder failure or leaky fitting(s). Other causes include: Air in the brake system; calipers not bled with bleed screws straight up; wrong size master cylinder (too small); calipers mounted on an equal plane with, or higher than the master cylinder; calipers flex excessively due to excessive pressure (over 1200 PSI); pedal ratio too great and excessive spindle deflection in corners causing piston knock-back. For further information review Wilwood’s Trouble Shooting Guide. You can also contact a Wilwood Sales Technician at 805-388-1188 or email Sales/Tech Support

Wilwood Engineering, Inc
4700 Calle Bolero
Camarillo, CA 93012
Phone: (805) 388-1188
Fax: (805) 388-4938

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