Brake master cylinder/hydraulic theory?

[Burning Angel]

Basicly the problem i have is this:

I have upgraded the brakes in my starlet to Gx60 on the front and lx76 in rear(or generic large T series diff drums) and now the pedal feel is quite heavy.

so it thought id put a larger master cylinder in to help(currently has the standard 3/4 one).

but then i thought wait, a smaller one would be easier to press but youd have to press it further to get the same caliper travel.

so what im asking is will a bigger master cylinder be helping the situation or making it worse?

options that i have found will fit:
KE70 = 13/16 which is smaller
r32/r33 skyline = 15/16 which is bigger

[Zak]

I though the master size altered the travel of the pedal, but it's the booster that will control the effort. So maybe going to a bigger booster will help, unless you need more/less travel?

also 13/16 is bigger than 1/4 (12/16)

[KinLoud]

and now the pedal feel is quite heavy.

What do you mean by quite heavy?
1 - long pedal i.e. large movement of pedal to make brakes work?
2 - hard pedal i.e. lots of force required to make brakes work but not much movement?

I would guess that you have more caliper piston area now so you should have more hydraulic advantage and a larger pedal movement (1)?

Maybe the brake pads aren't working very well or are overheating which could lead to (2)

Ken
Ham
021 408 863

[Burning Angel]

by heavy i mean i have to press quite hard to get the car to slow down.

it stops fine but you've got to make a conscious effort to do it.

so id say #2

the pads and shoes are brand new and have been properly bedded in.

i suppose it could be that it has a small booster but there is no way im gonna fit a bigger 1 in there.

[strx7]

if you have to get the pedal close tot he firewall to make it stop you need a bigger master cylinder. If the pedal is HARD and you'd like it to be softer, you need a larger BOOSTER

[fangsport]

if your mechanical and hydraulic advantage is correct, then a booster isn't needed.
are you running a bias valve?
how many outlets on he master cylinder?

[Burning Angel]

yes im running a bias valve. just the stock starlet one and the master has two outlets.

i havent had a chance to drive it properly as its not road legal and still has a few handling issues.