Master a Cylinder Bore - What's the Difference?

[Skull-1]

I am working my way through this disc swap on DoctorDiff's site and  I am stuck on which Master Cylinder bore to use. 

1 1/32" bore iron master cylinder for solid pedal feel (+$75.00)
15/16" bore iron master cylinder for maximum line pressure (+$75.00)

I am not a fan of a super stiff pedal but it can't be worse than the one I have now.   Any thoughts?   Can anyone translate this for me into real world terms?

[Ghoste]

It's difficult to say because only you can say what is too hard for pedal pressure to you.  For me, I would want the 1 5/16 one.

[Skull-1]

It's difficult to say because only you can say what is too hard for pedal pressure to you.  For me, I would want the 1 5/16 one.

What is the practical effect of both?   With the 15/16" bore am I gonna breathe too hard and lock up the brakes?  

Or if I go with the other am I gonna feel like I have no booster and have to use both feet?

I exaggerate of course...but....

[Ghoste]

Honestly I don't know that you'd feel a great deal of difference in pedal pressure between the two, some but I don't know if it would be huge.  For me, I like the bigger one to increase the clamping force on the calipers when needed.

[Skull-1]

Honestly I don't know that you'd feel a great deal of difference in pedal pressure between the two, some but I don't know if it would be huge.  For me, I like the bigger one to increase the clamping force on the calipers when needed.

Not to not pick but he is saying the smaller one boosts pressure.  I guess Bernoulli strikes again.  Is pressure the driving factor for clamping force?   I know I sound stupid but really I just want to insure I haven't missed something. 

[Pete in NH]

Hi,

You have to displace a certain volume of fluid from the master cylinder to actuate the wheel cylinders or calipers. The 1-1/32" master cylinder is going to move the required volume of fluid faster with less pedal travel. This will give you a harder pedal with less travel, kind of like stepping on a rock. The 15/16" master cylinder will require more travel to displace the required volume of fluid and have longer pedal travel and softer feel.

[Ghoste]

You know I was even paying close attention to the numbers there, I was talking about the 15/16 one being the one I would prefer but was reading it as 1-5/16.   

[Dino]

I'm wondering the same with mine, I have a Raybestos with 1-1/8" bore and I hope it's not too hard.  I hope to have it close to a modern pedal feel.  I drive 4 different cars and it's nice to have some things be fairly the same. 

[John_Kunkel]

Comparing the two in a typical manual brake setup with a 6-1 pedal ratio, with 100 lbs. of pedal pressure the 15/16" MC would provide a line pressure of 869 psi; the 1 1/32" MC would provide a line pressure of 717 psi....about a 20% advantage to the smaller MC.

All else being equal, line pressure is the driving force in clamping pressure.

[Skull-1]

I'm wondering the same with mine, I have a Raybestos with 1-1/8" bore and I hope it's not too hard.  I hope to have it close to a modern pedal feel.  I drive 4 different cars and it's nice to have some things be fairly the same. 

I have the same goal.