brake master cylinder - larger size makes for less or more pedal effort?

[Garrett]

On my 65 911, if I change the 17mm master cylinder to a 19mm one, will the amount of pedal effort required be less, meaning I can press less on the pedal and have the brakes come on harder?

And, would a vacuum boosted brake system like on later cars be a worthy addition?

I seem to have read different things - some people have said that the smaller size master cylinder will provide a greater amount of pressure to the calipers.

If the brake calipers were made larger, is that the time when a larger master cylinder would be needed to push more fluid?

Just curious - as I have read different things! My 964 has brakes like snot - my teeth feel like they'll come out when I barely hit the brake pedal. I want my early 911 to feel the same! Plus the safety of an updated dual circuit master cylinder would be nice!

Any suggestions???

Thanks!

[Steve@Rennsport]

Hi Garrett:

Installing a 19mm MC would be considered an upgrade and would not adversely affect your pedal effort. The pedal travel would be shorter.

We've done this for 25 years on 914's.

Now,................If you want to improve the brakes on your '65 closer to your 964, I'd suggest the installation of the 84-89 Carrera calipers & rotors. This will require
using later '72-89 "S" or SC-Carrera struts, ball joints, A-arms, and a few mods to your rear trailing arms for the Carrera calipers.

Its very doable and quite worthwhile.

[movin]

Assumming a static pedal pressure, wouldn't it reduce the hydraulic PSI to the brake cylinders when you increase the master cylinder diameter? So, in order to stop the car as quickly as before you would have to apply more pedal effort, but the pedal travel would be reduced.

[Steve@Rennsport]

A larger MC pushes more fluid per stroke of pedal and gnerally reduces pedal travel and raises pedal pressure (effort), all things being equal.

When someone installs calipers that have either larger pistons, or more caliper pistons, pedal pressures do not always go up linearly. Lots of variables here.

Brake pad materials also play a huge role in pedal efforts.

[carmaneddy]

Here is some physics for ya!

Increasing the size of the MC decreases the pedal travel for the same volume of fluid compressed. Since you change nothing at the wheels the you apply the same force to stop but you do less work. Because
work = force x distance.
Therefore increases in MC result in increases in Mechanical Advantage

Check out this link for a nice graphic.

<http://auto.howstuffworks.com/brake3.htm>

[Garrett]

Thanks everyone for your insight regarding this! Very helpful and interesting. As you mentioned Steve, I'll have to look into some different pads too - I didn't know they made that much difference in pedal effort.