Sprint rear brake bias valve.

[new to this]

I think the Fords are 54mm single piston.

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

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

[sprint95m]

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.

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.

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

[sprint95m]

I think the Fords are 54mm single piston.

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

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.

[new to this]

I think the Fords are 54mm single piston.

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

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.

Ian

Yes the KA, fiesta and puma 1.4 are vented disc,.didnt know the disc size was cast in the body

Dave

[SprintV8]

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.

[GrahamFountain]

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.

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.

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

Interesting. But remember that, if you change the cross sectional area of the master cylinder by the same factor as you change that of the the slave cylinders, you keep the pedal travel the same, but go back to the same ratio of forces between pedal and brake pad, i.e. defeat that aspect of the upgrade. What is the master cylinder diameter on the Sprint anyway?

BTW. Am I right in thinking the smaller 1850 servo will require less pedal movement but more input force for the same output force than the bigger Sprint servo, being a smaller gain device?

What I remember about Maxwell is spending hours going through clever ways to avoid solving his equations in Andy Marvin's course on antenna design, because they're too hard to solve at undergraduate level.

With respect to Dr (now Prof I think) Marvin's forename: I'm reliably informed Andy is not short for Android. His level of paranoia is not something I could comment on. But I have to suspect the sanity of someone who claims they can prove that power goes into a resistor sideways. Not sure if that was what caused the pain in all the diodes down his right side though.

[GrahamFountain]

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

[SprintV8]

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

I think the early fords have two piston callipers
Escorts-Granada’s-Cortinas.
But changed to the single piston I think because it was cheaper to manufacture.
Sierras Escort Fiesta KA.

[cliftyhanger]

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

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.

[GrahamFountain]

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

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.

Well, sort of behaves like a twin piston caliper. Except that it applies only half the force between the two pads for the same hydraulic pressure. Hence, given that the pads are a good approximation to a true solid material, only half the brake force of a twin piston caliper. And I've not been allowing for that.

What happens to pedal movement for the same brake force at, all else being the same, twice the hydraulic pressure, is an interesting question. And one I don't have a quick answer to. I think the single piston caliper should takes a bit less pedal travel, but I also think it's rather more than half as much.

Graham

[jikovron]

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

[GrahamFountain]

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

If the two pads start the same distance off the disc in both cases, the single piston has to move twice as far, to move both the directly and remotely operated pads, and that would take twice the volume of fluid. But I'm not certain that has the right initial conditions for the single piston caliper. I'm sure though, that the two pads don't start half as far off the disc as with the two cylinder caliper. I also think there will be more flex in the pipework at twice the pressure, but whether or not that's linear isn't clear to me.

Graham

[jikovron]

I'm theory the pads have the same running clearance and such travel the same distance to meet the disc before pressure buolds, 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.

[GrahamFountain]

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.

Yes, the one piston uses the same fluid as two at the same hydraulic pressure. But to get the same brake force, it needs twice the hydraulic fluid pressure on that one piston to apply the same force to both of two pads. That's because it has half the area of two pistons and the force is the hydraulic pressure times the total piston area. So there's more give in the system at twice the pressure. It may not be twice as much, indeed I think its less. But it must more at the same brake force.

Graham

[Carledo]

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

I've studied both pics and both seem to contain the same error expressed different ways as regards the Sierra piston placement.

In the first drawing, the Sierra pad/piston placement is correct, there is a slight overlap of the piston to the body of the pad at the outer edge (in real life, pads have a small crescent bulge to accomodate this, not shown in the drawing, but its lack is immaterial to our calcs) but the pad/disc placement is wrong, showing the body of the pad overlapping the disc by maybe 5mm or so, this is not correct, the body of the pad starts around 1mm IN from the edge of the disc.

In the second drawing, the disc/pad placement is correct, but the pad/ piston placement is incorrect meaning that in both drawings the piston centre for the TJs is too far out by 5mm or so (I can't be more accurate than that without scaling the drawing and measuring, something my computer skills arent up to, i'll try to calculate it from available data for my next post)

However, I agree that once that error is corrected, we should have a basis to calculate from, everything else seems satisfactory.

I also have some used Puma pads in my garage which were marked in service by the piston on the piston side face and clearly show the relationship between pad and piston placement. I'll take a pic tomorrow, too cold, wet and windy to go out there tonight.

Steve