Calculations I have done regarding brakes
| Master Cylinder Size MM | Line Pressure PSI | Pedal Ratio | Pedal Load LBS | Master Cylinder Input LBS | Master Cylinder Output PSI |
| 0.812 | 0.518 | 3.300 | 50.000 | 165.000 | 318.627 |
| 0.812 | 0.518 | 3.300 | 100.000 | 330.000 | 637.253 |
| 0.812 | 0.518 | 3.300 | 150.000 | 495.000 | 955.880 |
Download the excel spreadsheet here
Clutch Calculations
Had to do some calculations in order to match my clutch master cylinder to my slave cylinder as the westfield supplied one did not seem adequate to release my clutch.
The slave cylinder is an SD1 item which has a bore of 7/8" (0.875). The slave pushrod needs to move the release arm 20mm in order to move the release bearing at least 10mm.
The master cylinder supplied by Westfield has a bore of 5/8" (0.625). The pedal moves the master pushrod by 30mm by design. My measurements indicated that this was 27mm but accepting that my measurement could be inaccurate due to the constrained area.
First I calculated the threotical maximum movement of the slave pushrod when the master is moved by 30mm:
So the master bore of 0.625" or 15.875mm displaced by 30mm gives a volume displacement of (15.875/2) * (15.875/2) * PI * 30 = 5938 cu. mm.
Now the slave bore of 0.875" or 22.225mm for each 1mm of displacement requires a volume of (22.225/2) * (22.225/2) * PI = 388 cu. mm
So if the master pushrod is moved by 30mm then the slave pushrod is moved by 5938 / 388 = 15mm, which is proven as insufficient to obtain clutch release.
So it is clear that the master cylinder needs to displace more hydraulic fluid for the same master pushrod distance travelled. I looked at the next master cylinder size up which is 0.700".
Master bore of 0.700" or 17.78" displaced by 30mm gives a volume of (17.78/2) * (17.78/2) * PI * 30 = 7449 cu. mm.
So the slave would move a maximum of 7449/388 mm = 19mm. I think this might work but at best the biting point would be on the floor so the next size up should be considered. The problem is though that the bigger the master bore the harder the pedal feel.
Master bore of 0.750" or 19.05" displayed by 30mm gives a volume of 8550 cu. mm.
Slave pushrod would be moved by 8550/388 mm = 22mm.