Brake And Clutch Cylinders

[Thrashed]

Hi all.

 

As a part of my engine swap i have decided to go down the route of floor mounted pedals rather than the standard GBS pedal box. Never liked the set up or the way all the pedals are bolted together and when you move the brake or clutch pedal it moved the other.

 

I am swapping from standard sierra front calipers and rear drums to mondeo mk3 front calipers and leaving the rear on drums.

 

I currently have a cable clutch but will have to swap to hydraulic clutch.

 

Now the pedal box i am looking to buy has an adjustable brake pedal ratio of 4.9-5.24:1 ratio, but i am unsure of the clutch ratio at present.

 

Now the big question is, how do i calculate the clutch and brake master cylinder sizes? The clutch slave i am planning on using is the standard mx5 mk3 which i believe is 0.625" (yet to confirm 100%).

 

I have googled this and it has blown me away!! Has anyone got a simple calculation to work out the sizes i will need.

 

Thanks in advance.

 

Steve

[brumster]

I calculated all of these when swapping the brakes on the rally car, right down to piston sizes in the caliper. It's pretty simple really, just a swept volume calculation based on the diameter of the pistons at each end. If you know what the previous ratio was on the standard brakes (ie. you know the piston diameter on the calipers, and the diameter at the master cylinder end), then you can calculate a ratio. From there, we can work out that if you change the diameter at one end but want to maintain the ratio, you can work out what you need to change the other end to. Or if you're not happy with the ratio, and want more braking power for less effort (but more pedal travel) then you can tweak the ratio up or down to suit.

 

Do it at club night if you like?

[Thrashed]

I calculated all of these when swapping the brakes on the rally car, right down to piston sizes in the caliper. It's pretty simple really, just a swept volume calculation based on the diameter of the pistons at each end. If you know what the previous ratio was on the standard brakes (ie. you know the piston diameter on the calipers, and the diameter at the master cylinder end), then you can calculate a ratio. From there, we can work out that if you change the diameter at one end but want to maintain the ratio, you can work out what you need to change the other end to. Or if you're not happy with the ratio, and want more braking power for less effort (but more pedal travel) then you can tweak the ratio up or down to suit.

 

Do it at club night if you like?

Awesome, thanks Dan

 

My current set up is standard sierra calipers and master cylinder. Let me know what figures you need and i will try and get all the info in preparation.

 

Cheers

 

Steve

[brumster]

...and you're happy with pedal effort/travel right now yes, so just happy to keep it roughly the same...?

[Thrashed]

...and you're happy with pedal effort/travel right now yes, so just happy to keep it roughly the same...?

Yes, but it will all be fitted into a different pedal box with a pedal ratio of around 5:1. I am not sure what the GBS ratio is?

Edited October 26, 2018 by Thrashed

[brumster]

Measure the lengths on the pedal between :

- pivot point to centre of the clevis pin operating on the brake cylinder rod

- pivot point to centre of pedal

 

Divide the big by the small, you've got your current pedal ratio

 

Piston diameter on the caliper end - I think standard Ford Girling single-pot sliding caliper might be 54mm?

Piston diameter on your new calipers, and how many actuating pistons there are, if it's more than 1. Might be 57mm for Mondeo?

Master cylinder diameter (bore) current... wassat on a Sierra?

[Thrashed]

Measure the lengths on the pedal between :

- pivot point to centre of the clevis pin operating on the brake cylinder rod

- pivot point to centre of pedal

 

Divide the big by the small, you've got your current pedal ratio

 

Piston diameter on the caliper end - I think standard Ford Girling single-pot sliding caliper might be 54mm?

Piston diameter on your new calipers, and how many actuating pistons there are, if it's more than 1. Might be 57mm for Mondeo?

Master cylinder diameter (bore) current... wassat on a Sierra?

Not sure what those bits are as yet, still need to buy the items.

 

Once I have the bits I will let you know, catch up on Sunday or Wednesday for some theory.

 

Cheers

 

Steve

[marlin]

Hi,

Hopefully attached are 3 spread sheets I've gathered during my 2 car builds. No experience with them and they are a bit anal but internet information is "you get what you pay for". If someone needs these to be forwarded direct feel free to contact me. Hope they are some help.

Marlin

 

oops; Error You aren't permitted to upload this kind of file

I guess no Excel spreadsheets allowed? If anyone would like them let me know.

[Thrashed]

Hi,

Hopefully attached are 3 spread sheets I've gathered during my 2 car builds. No experience with them and they are a bit anal but internet information is "you get what you pay for". If someone needs these to be forwarded direct feel free to contact me. Hope they are some help.

Marlin

 

oops; Error You aren't permitted to upload this kind of file

I guess no Excel spreadsheets allowed? If anyone would like them let me know.

PM sent. Thanks

[marlin]

spreadsheets sent. Let me know if any problems with them coming across the pond.