[birabrakes] 80tq: Master Cylinder Revelations

[JShadzi at aol.com]

   Teddy, I suspect that what you are saying is that going to a biger MC 
essentially reduces line pressure, but with vacuum power assist, the point is 
really mute.  The fact that the the bigger MC is moving more fluid into the 
bigger calipers is the key and reason to the upgrade.  I tested my original 
22mm MC, and it was leak free and held brake line pressure consistently.  
Also, knowing that Porche/Audi used the same MC in the RS2 which used 
similarily sized Porche Calipers makes me feel very comfortable about the 
upgrade, besides the fact that I greatly enjoy the increased feel and 
performance of the brakes since the upgrade.  My original recommendation 
still stands for those who are using larger calipers with 22mm MC's...
Javad

<< javad,
i don't doubt that the new MC helped, but i'd like to point out that the 22mm 
MC would give you more "leverage" than the new 25.4mm MC
that you installed.  the hydraulic ratio of the MC bore to the caliper piston 
bores changes when you change the MC, and in this case, you changed it so 
that the MC displaces more fluid when the brake pedal is depressed.  this 
results in higher pedal effort, but a more solid pedal with better feel.
   i suspect your old MC was dying, and replacing it with a new 22mm MC would 
have made an even bigger difference in reducing pedal effort. replacing the 
rear flex lines with braided steel hoses helped, too,
especially if the old ones were expanding under pressure.
-teddy>>