paul jacobs Posted August 11, 2014 Share Posted August 11, 2014 Can anyone confirm if I'm right in thinking that the difference between the standard brake master cylinder and the 'competition' one is that the comp. m/c has a larger bore, which gives a shorter pedal push? Link to comment Share on other sites More sharing options...
Area Representative Richard Price Posted August 11, 2014 Area Representative Share Posted August 11, 2014 Quoting Paul Jacobs: Can anyone confirm if I'm right in thinking that the difference between the standard brake master cylinder and the 'competition' one is that the comp. m/c has a larger bore, which gives a shorter pedal push? The standard master cylinder is 5/8" bore, and the AP "uprated" master cylinder is 13/16" bore. Therefore, to achieve the same stopping force, around 1.67 times the pedal pressure is required, with a corresponding reduction in pedal travel. Link to comment Share on other sites More sharing options...
Pendennis Posted August 11, 2014 Share Posted August 11, 2014 And it has two circuits (front and rear) with two separate inlets via a common reservoir. In theory if you get a failure in one of the circuits the other should offer some braking. Link to comment Share on other sites More sharing options...
paul jacobs Posted August 11, 2014 Author Share Posted August 11, 2014 Thank you both, yes I should have expanded, and said, "which gives a shorter pedal push" and correspondingly harder pedal Is the standard m/c not dual circuit as well? Link to comment Share on other sites More sharing options...
Area Representative Paul Richards Posted August 11, 2014 Area Representative Share Posted August 11, 2014 Quoting Pendennis: And it has two circuits (front and rear) with two separate inlets via a common reservoir. In theory if you get a failure in one of the circuits the other should offer some braking. A standard master cylinder also has two circuits. I think I'm right in that it is just the cylinder diameter that is different. Link to comment Share on other sites More sharing options...
oldbutnotslow Posted August 11, 2014 Share Posted August 11, 2014 Reproduced from CBS on line A common question is 'What bore size master cylinders should I use? In theory, it is possible to determine the correct size of the master cylinder (piston diameter) by calculating pedal ratio, pedal travel and caliper piston diameters but it's often easier to 'suck it and see' by choosing a .750" master cylinder to begin with and working from there. Many factors will determine the optimum master cylinder size such as weight of the vehicle, tyre diameter, brake pedal length, weight distribution and servo or non- servo assistance. Brake pedal ratio is often the easiest parameter to change. Increasing the pedal length is, in effect, increasing the leverage but the pay-off is less fluid movement for a given pedal travel. If the pedal is 12" long from the fulcrum to the foot pad and the cylinder push rod is 3 inches from the fulcrum then the pedal has a 3 to 1 ratio. Increasing the ratio to say 4 to 1 will give more leverage but with longer pedal travel. For a clutch the same rules apply to the release fork. A higher ratio will make the clutch action easier but there will be less travel of the release bearing. Determine the distance the release bearing has to travel to fully disengage the clutch (usually about 10mm) and work backwards from there. A release fork with 2 to 1 ratio will require 20mm travel of the slave cylinder. Brake hydraulics is really all about fluid movement so, to give you an idea of the effect of changing master cylinder sizes, here's a chart of how much fluid each size master cylinder moves with each l cm travel of the push rod. You can see that a 1" cylinder will move 2 ½ times more fluid than a .625" cylinder. But the pedal will require 2 ½ times more force to get the same braking performance. However, the pedal travel will be 2 ½ times less. Cylinder Piston Diameter Fluid movement for 1cm of piston travel 0.625 ( 5/8”) 1.98cc 0.75 (3/4”) 2.85cc 0.825 (7/8”) 3.45cc 1” 5.06cc So a bigger MC is not necessarily the best thing. It all depends. Link to comment Share on other sites More sharing options...
Myles Posted August 12, 2014 Share Posted August 12, 2014 Certainly happier with the uprated one when I fitted it - couldn't get a good pedal (firm) with the standard one, but it might also have less than perfect seals, so maybe not a dingle variable. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 12, 2014 Member Share Posted August 12, 2014 Quoting Myles: Certainly happier with the uprated one when I fitted it - couldn't get a good pedal (firm) with the standard one, but it might also have less than perfect seals, so maybe not a dingle variable. , didn't know about the seals. ;-) Jonathan Link to comment Share on other sites More sharing options...
paul jacobs Posted August 12, 2014 Author Share Posted August 12, 2014 The seals are invariably there in the background, they do a really important job, but the dingle always gets the glory. 😔 😬 Link to comment Share on other sites More sharing options...
Rob Walker Posted August 12, 2014 Share Posted August 12, 2014 I found that the uprated MC helped me compensate for pad knock off and high brake temps/long peddle on track. It takes some getting used too as it has a very dead feel and is not to every bodies liking. Link to comment Share on other sites More sharing options...
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