i have a 93 civic delsol si. it comes stock with the 13/16th inch master brake cylinder. i decided to replace it with a 91 EX civic sedan master cylinder, which is 15/16th inch (a direct bolt on replacement)

the problem:
now the pedal definitely has a less sponginess feeling, but i have to push the pedal wayyyy harder to get the car to stop the same as before. its hard to get the wheels to lock too. what do you guys thing it might be?

 

larger diameter master cylinder will have less leverage on the brakes. what you are explaining is exactly what will happen. most people dont upgrade the master cylinder unless using larger brakes that require the extra volume.

not a direct analogy, but imagine taking a screwdriver and stabbing it in the wall. now imagine turning it around and trying to stab the handle through the wall. it will be significantly harder. you are trying to move a larger surface area piston (ie the handle vs. the point of the screwdriver), and thus volume of liquid, with the same force, so the resulting pressure per unit of area created will be less (in this application, the pressure seen by the calipers).

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by redrum eg6 &raquo;</TD></TR><TR><TD CLASS="quote">larger diameter master cylinder will have less leverage on the brakes. what you are explaining is exactly what will happen. most people dont upgrade the master cylinder unless using larger brakes that require the extra volume.

not a direct analogy, but imagine taking a screwdriver and stabbing it in the wall. now imagine turning it around and trying to stab the handle through the wall. it will be significantly harder. you are trying to move a larger surface area piston (ie the handle vs. the point of the screwdriver), and thus volume of liquid, with the same force, so the resulting pressure per unit of area created will be less (in this application, the pressure seen by the calipers).</TD></TR></TABLE>


nice

 

Did you bench bleed it?
Are you using larger calipers?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by redrum eg6 &raquo;</TD></TR><TR><TD CLASS="quote">larger diameter master cylinder will have less leverage on the brakes. what you are explaining is exactly what will happen. most people dont upgrade the master cylinder unless using larger brakes that require the extra volume.

not a direct analogy, but imagine taking a screwdriver and stabbing it in the wall. now imagine turning it around and trying to stab the handle through the wall. it will be significantly harder. you are trying to move a larger surface area piston (ie the handle vs. the point of the screwdriver), and thus volume of liquid, with the same force, so the resulting pressure per unit of area created will be less (in this application, the pressure seen by the calipers).</TD></TR></TABLE>


I bet he has to push with (15/13)^2 times the force. That's 133% greater than stock. Get some calipers with larger piston bores to compensate.

 

yeah i have stock calipers. i see what all of you guys are talking about, but i didnt understand the caliper analogy. P=(F)/(A) but i didnt think it was goign to be that much harder over stock. i just wanted to get rid of that spongy feeling i had with stock brakes, i got rid of it, but now i gotta push harder.

I bought a reman MC from kragen, im thinking of returning it and just rebuilding my old 13/16


Modified by duh blacksheep at 8:35 PM 4/24/2005


Modified by duh blacksheep at 8:36 PM 4/24/2005