I have sierra master - bore 22.2 mm with cortina caliper (diameter 54 mm).

I haven't measured how far the pistons move when brakes are fully engaged but would guess about 1-2 mm - anyone know or how I can mesaure this?

so let's say 1 mm, then that means mc piston moves 24 mm - sound about right?

I am think of remaking the brake peda lso what would be a good ratio? (I know it is a compromise between peda lpressure, peda lpad movement etc. ) ... so if someone has the same or similar master/calipers, what are you using?

(In case you are wondering, I want to shorten the brake pedal whcih affects the ratio since the pad lines with my instep as opposed to ball of my foot - big feet you see).

Dont you want to lengthen it?

Mine are floor mounted - hence question?


I assume the pivot is fixed, therefore if you want to operate pedal against a certain part of foot then i guess you dont have much choice about length and hence ratio.

[Edited on 1/8/07 by DarrenW]

I am guessing that you have pendulum pedals if you need to shorten them. It is quite feasable to change the m/c pivot point to increase the pedal ratio - a 5:1 ratio about right but without a servo the bigger the better.

You dont work this out from pad movement but braking effort required.

The pad will move on first application of the bakes and fluid will fill the lines to take up this 'slack' but the pad will not return 2mm but stay in light contact with the disc.

The attached spreadsheet will give you idea of what you need.

pedals are top mounted, custom "pedal box" using mk2 escort brake and clutch pedal.

The only thing that is very fixed is the postion of the master cylinder; I think I can move the pivot - will require fabrication but less than having to move the master (if I did that, I would need to re-wire the rear pipe whcih is BIG deconstruction jb!)

When you move the pivot, watch the angle of the m/c pushrod doesn't move too far away from the 90 degree angle when applying pressure.
I managed to improve my ratio from 4:1 to 5:1 by moving the pivot 10mm - made a hell of a difference to the pressure required to brake.