oister Posted May 1, 2006 Share Posted May 1, 2006 As the topic said, anyone thought about upgrading to the larger brake master cylinder? Legacy ones are 15/16", the STI one is 1 1/16" I think. For those who are fortunate enough to see both cars all the time (shop or owners), do the two units look like they would swap? Link to comment Share on other sites More sharing options...
derffred Posted May 1, 2006 Share Posted May 1, 2006 i have noooo clue, i'm still debating if i should swap over STi brakes... Link to comment Share on other sites More sharing options...
OBieXT Posted May 2, 2006 Share Posted May 2, 2006 Not sure that would be an upgrade. If your measurements are at all accurate, it would mean you'd have to step on the brake pedal 28% harder to develop the same line pressure to the calipers. The hydraulic advantage in a brake system depends on the ratio between the master cylinder's bore and the wheel cylinder (caliper) bore. You'd be going the wrong direction by installing a larger master. Pedal stroke would be reduced at the expense of requiring greater effort. Link to comment Share on other sites More sharing options...
RobY Posted May 2, 2006 Share Posted May 2, 2006 That is correct. The STi master cylnder has 28% less mechanical advantage. Link to comment Share on other sites More sharing options...
edmundu Posted May 2, 2006 Share Posted May 2, 2006 I've got Brembo's all around, and I think the stock MC does just fine:icon_bigg ! Brake pedal input is immediate & firm as well. It certainly increased the pedal responsiveness over stock, but I thought it might have had to also do with the ds2500 pads? Either way, I love the braking action.... One question....Doesn't the LGT's vacuum booster have a different ratio as well, effectively changing the pedal pressure required? Link to comment Share on other sites More sharing options...
robinlsb Posted May 2, 2006 Share Posted May 2, 2006 Not sure that would be an upgrade. If your measurements are at all accurate, it would mean you'd have to step on the brake pedal 28% harder to develop the same line pressure to the calipers. The hydraulic advantage in a brake system depends on the ratio between the master cylinder's bore and the wheel cylinder (caliper) bore. You'd be going the wrong direction by installing a larger master. Pedal stroke would be reduced at the expense of requiring greater effort. +1 on that, not to mention the havoc it would play with ABS and EBD. "Belief does not make truth. Evidence makes truth. And belief does not make evidence." Link to comment Share on other sites More sharing options...
Opie Posted May 3, 2006 Share Posted May 3, 2006 One question....Doesn't the LGT's vacuum booster have a different ratio as well, effectively changing the pedal pressure required? Not sure about the pressure...but the LGT & STI vacuum boosters are different part numbers: 2005 LGT: Vacuum Booster - 26402AG05A Master Cylinder - 26401AG010 2005 STi: Vacuum Booster - 26402FE000 Master Cylinder - 26401AC191 Link to comment Share on other sites More sharing options...
oister Posted May 3, 2006 Author Share Posted May 3, 2006 Not sure that would be an upgrade. If your measurements are at all accurate, it would mean you'd have to step on the brake pedal 28% harder to develop the same line pressure to the calipers. The hydraulic advantage in a brake system depends on the ratio between the master cylinder's bore and the wheel cylinder (caliper) bore. You'd be going the wrong direction by installing a larger master. Pedal stroke would be reduced at the expense of requiring greater effort. That is kinda the point, a shorter stroke. I prefer the feel of grabbing brake with a shorter stroke at the expense of "firmer" brake pedal. I guess its all preference...since I consider a "firmer" pedal better than a "mushier" pedal. It makes heal-toe a bit easier too since I wouldn't have to bring the heal back up as much, at a given brake force. Link to comment Share on other sites More sharing options...
rao Posted May 3, 2006 Share Posted May 3, 2006 BBK looks cool, new master cylinder doesn't; therefore no master cylinder upgrades unless someone starts making colored master cylinders Rob IF YOU CARE ABOUT YOUR CAR YOU SHOULD NEVER DRIVE IT Link to comment Share on other sites More sharing options...
dirteemac Posted September 1, 2009 Share Posted September 1, 2009 Legacy's only have a 15/16th's bore? Shoot my stock mc on my forester has a 1". Link to comment Share on other sites More sharing options...
robinlsb Posted September 5, 2009 Share Posted September 5, 2009 BBK looks cool, new master cylinder doesn't; therefore no master cylinder upgrades unless someone starts making colored master cylinders :lol: Holy Cra*. Are intimating that a BBK will not stop in shorter distance than standard brakes on the street!!!!!!!!!!!!!!!!!!!!!!!!!!! Cripes, I have to stop tailgating;) "Belief does not make truth. Evidence makes truth. And belief does not make evidence." Link to comment Share on other sites More sharing options...
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