Brake piston size

[CobraStang]

My original front calipers are rather chewed up. They are two piston calipers, with 38mm pistons. The new 03-04 calipers use 40mm pistons.

I figure there will be more pedal travel with the larger pistons, but will it be significant?

[rmicroys]

Why not upgrade your master cylinder when you upgrade your calipers? I would assume that the master may be different as well? Why not swap that too, then you have nothing to worry about.

[Carguy]

Good point Rob. I changed my front calipers last spring without a master cylinder upgrade. The calipers are single pot Integra Type R with a significantly larger diameter piston than stock. As it turns out there is not much difference between a Base RSX and a Type S master cylinder - Base is 15/16" diameter and Type S is 1" diameter. With the stock master cylinder I get more brake pedal travel when my race pads start to get thinner at about 50%-33% pad left. When I put my street pads back on after an event brake pedal travel is retored to normal height. Swapping to the Type S larger diameter master cylinder should remedy this for next season.

[haniforama]

I went from 13/16" with a small booster to 1" with a HUGE booster.

I swapped to significantly larger front calipers and swapped from rear drums to disks.

Brake pedal is rock solid and pedal travel is minimal with excellent feel.

Your brakes cannot be too good :D

[Carguy]

Originally posted by haniforama
I went from 13/16" with a small booster to 1" with a HUGE booster.

I swapped to significantly larger front calipers and swapped from rear drums to disks.

Brake pedal is rock solid and pedal travel is minimal with excellent feel.

Your brakes cannot be too good :D

Hanif, I would say my brakes are "not optimized". ;)

I always have solid pedal feel thanks to the Ferodo DOT 5.1 brake fluid and SS brake lines. My greatest shortcoming is that brake pedal travel changes with pad thickness. :(

The booster and the rear calipers/rotors in the Base RSX and the Type S are identical. The front Type S calipers are slightly different from the front Type R calipers (both are single pot but of different shape - piston diameter unknown but larger than stock) as is the front rotor diameter (11.1" Type R vs 11.8" Type S vs 10.3" stock). As noted above the stock master cylinder is 15/16" in diameter and the Type S is 1". Not a huge difference but significant enough to make the swap.

I also have a bit too much front brake bias which I intend to remedy with rear pads that have more bite than my crap EBC pads. When I swap the master cylinder and higher friction rear pads I will be closer to an "optimized" setup. :p

[CobraStang]

I understand that the 03-04 Master Cylinders are 1-1/16", so a bit larger than the 1" MC that's in my car. For $220, I'm thinking it may be a good upgrade. But I want to do my homework first.