I'm looking to upgrade the brakes on my e type, it has modern 4 pot calipers, but still has the old master cylinder / servo setup, which the diagram below shows is unneccesarily complicated - J & K are the lines to the front and rear brakes, P & Q are vacuum lines to the manifold and vacuum reservoir.

There isnt room in front of the pedals for a modern servo / MC setup, so what I'm thinking, is to use a single line master cylinder at the pedal, connected to a clutch slave cylinder. Then use the clutch slave to activate a modern servo / MC, mounted in place of the existing servo at the passengers side.

I could use a single circuit, and remote servo, but would really like the 3+ to 1 boost from a modern servo as opposed to 1.9 - 1 from a remote.

I know the weak link is the single line master and slave, but, this is no less than the existing setup.

What do you think?




brake schematic

[Edited on 9/10/11 by r1_pete]

I am looking at removing the master cylinder from my fiesta for trackdays so can understand this a little.
I would say try and determine what you want the brakes to be suitable for, do you want good road performance or flat out race-spec handling?
Road braking systems have less pedal effort required for as given braking performance hence the requirement for servo-assistance due to low pedal effort and low pedal ratios.
Racing brakes can dispense with the servo because high pedal effort and ratio can be used.
Sorry this is not a clear answer but I am still working on my understanding through the mathematics.

It will be 100% road use, I'd like a modern low effort feel to the brakes, my Mrs. drives the car too, and although she understands it is 45 years old, I'd like teh brakes a little more usable for her.

Plus, the complexity of the existing setup makes any fault diagnosis a mamoth task.

The E Type system was a pita but what you are considering just introduces more potential failure points --- the system will in effect be single circuit and won't be fail safe it will in fact more likely to fail than a single circuit system.

It would make more sense to use two separate remote servos, Alfa did this in the early 1970s using 2 Lockheed remote servos (same servo as used on Hillman Hunter and MGB ) this setup should fit in the space in the left side of the car. If you want to reduce the pedal effort more go down one size in master cylinder bore.

Don't forget that if you go down in bore size, you increase the pedal travel(because the brake caliper piston needs the same volume of fluid to make it move the current amount), and decrease the maximum volume of brake fluid that can be passed to the calipers - check neither of these will give you a problem!

Changing the pads can make quite a difference - mintex 1144s have a coefficient of friction about 1.25* that of a 'standard' pad.

Regards
Hugh