If your clutch pedal is hard to push, the first thing to check is for any binding in the linkage between your clutch pedal and the master cylinder. Secondly, check to make sure you have not created too steep of an angle in the actuation of the rod moving in and out of the master cylinder.
Next, verify your pedal ratio is within specification. The pedal ratio is the distance that your foot moves versus the distance the rod going in and out of the master cylinder moves. Pedal ratio is an important component in creating a smooth pedal feel with excellent clutch modulation. One of the biggest mistakes made in hydraulic conversions is creating a low pedal ratio.
Ideally, you want between 5:1 and to 6:1 ratio. This means essentially that if your master cylinder rod moves 1”, your foot needs to moves 5-6”. The Wilwood master cylinder supplied with our Hydramax kits require 1.12″ of travel; this means that your pedal needs to move 6″ to achieve a 5:1 ratio. Most stock pedal pivot points give an excellent pedal ratio, however if you move the rod lower on the pedal, or you are building a custom car and you have a ratio lower than 4:1, you may consider artificially raising the point at which the pedal rod hits the pedal arm to increase this ratio. If this is not possible, you can also consider moving the master cylinder bracket assembly lower on the firewall to increase the rod angle and therefore the pedal ratio.
To determine the ratio of the pedal, you need to do some measuring. There are two measurements you need to take: the length from the pivot (fulcrum) of the pedal to the pushrod hole (Y), and from the fulcrum to the center of the brake pedal (X). The formula is X/Y=Ratio. For example, your stock clutch pedal is 14 inches long (X), with a pickup point measuring 4 inches from the center of the fulcrum (Y). 14/4=3.5, which is 3.5:1. While this may have worked for the factory manual linkage, it is about half of what it needs to be for a hydraulic set up. In this situation, 100 pounds of foot pressure yields 350 pounds of pressure to the master cylinder. Move the pickup point up 1.75 inches, (Y measurement of 2.25”), and that same 100 pounds of foot pressure yields 600 pounds at the master cylinder.