I think the Fords are 54mm single piston.

This should help.
https://brakeparts.co.uk/

As a general rule bigger brakes make it necessary to move the pedal further to give the same braking force on the road because the (generally) bigger cylinders take more fluid to move the same distance. That's certainly one reason for using, e.g., smaller rear wheel cylinders and so reducing their effect. Using bigger back brakes with bigger front brakes is likely to make that lengthening effect even worse.

Thanks that site helped,but not all ford calipers are 54mm pistons,the KA and fiesta,Puma 1.4 are 48mm pistons

Also Dave, with the smaller piston calipers you need to make sure they are for vented discs.
The piston size is cast onto the caliper body.


Ian.

As a moderator I am expected to try and read through posts on here.
Well this thread is doing my head in, big style.

I am not going to attempt to interpret all that has been written,
but this one doe stand out like the proverbial sore thumb. Brake master and slave cylinder sizes are matched.
Sierras have 22.2mm bore master cylinders, so changing the BMC on a Dolomite to this size eliminates any excessive brake pedal travel for the set up being discussed here,
since the cylinder sizing is as per the Sierra (2 litre petrol).


As to the stuff about "O" levels and maths,
what is the point of research and development and testing?

James Clark Maxwell may have done everything with pure mathematics, but he was truly exceptional
( and is sadly rather forgotten in his homeland but not in Russia it seems).


thanks,
Ian

The KA and Fiesta I looked up where both 54mm
I didn’t go thru all the ones listed.

But dare say there is other sizes.

Um, but do all these Ford calipers have only one piston, like half the effective hydraulic area you'd normally expect?

Graham

Um, but do all these Ford calipers have only one piston, like half the effective hydraulic area you'd normally expect?

Graham

That would be the case, except the piston acts on both pads via the slider. You need to get your head around that!
So behaves like a twin piston caliper.

Single piston caliper = twin piston caliper if the piston area is the same, including the hydraulic fluid volume will remain the same.

I'm theory the pads have the same running clearance and such travel the same distance to meet the disc before pressure builds, such that the fluid volume used in each case remains the same, also the fluid pressure of each will be equal for the same brake force.

Trying to redo the calculations, I've been back and looked for what I have and find this drawing. Can we confirm that it's at least close to correct in the dimensions for the placement of the pads and pistons for the Sprint and Sierra front brakes?

I suspect the difference between the centroid of the pad and the centre of the Sierra piston isn't important. So a measure from hub to piston centre, which should be easier to make, will probably be enough at the level of accuracy that's needed here.

Graham