Re: Wilwood Master Cylinder Conversion

Posted by HH56 On 2019/1/10 10:15:39

The problem with installing any modern system is pedal ratio. Packard placed the Treadlevac at the bottom of the pedal for a 1:1 ratio. 100 pounds of foot strength equals 100 pounds to the master.

The Treadlevac has a solid approx 5/8" diameter rod which moves in a fairly long stroke into a closed cylinder and displaces a volume of fluid out to the wheels equal to the rod volume that was inserted into the cylinder. That arrangement can cope with the 1:1 pedal ratio because the rod in effect very efficiently squeezes the fluid out of the confined space with the booster section adding to the foot force.

Modern masters use a fairly large diameter piston to push fluid ahead of it and out to the wheels. The larger diameter piston needs less stroke for the volume but because of the larger surface area needs more force to push the fluid out in an adequate strength. The piston gets the additional force by using a pedal ratio of approximately 4:1 along with the booster to provide the additional force if a power brake system or a ratio of approx 6:1 if strictly a manual system. 100 pounds foot strength on a power brake system equals 400 pounds plus whatever the booster adds or if a manual system, 600 pounds to the master.

In order to get the additional pedal ratio the master must be moved from the bottom of the pedal where Packard placed it and mounted so the connection between the pedal arm and the master unit is higher up on the pedal arm. The closer the connection is to the upper pivot equals a higher ratio but shorter stroke so there is a tradeoff in finding the best location. Many have installed modern universal boosters and dual masters in the opening for the air vent or even higher on the firewall and made custom pedals to work with the chosen location. Others have kept the original bottom of pedal location but have severely modified and relocated the pedal components inside the car to provide the additional ratio. Neither option provides a stock appearance.

You can do a search on the forum for BTV or brake replacement or modern brakes or several other similar titles for various threads where people have documented their approaches. The air vent location seems to provide the best overall looking and possibly easiest to mount arrangement but does sacrifice the vent function.