# Twin brake master cylinder sizes????



## lukey-babes (Apr 2, 2009)

Im curently doing a brake convertion on my mk1 and doing a twin master cylinder setup and deleting the brake servo.
Im doing g60 280mm callipers or normal gti brakes at the front.
And doing mk2 16v callipers at rear or mk4 brake callipers.
Does anybody know all the piston sizes on the callipers so i can determine what size master cylinders to run?
Also on a twin master cylinder with bias bar setup have 2 different size master cylinders as long as they have the same stroke length?
I have been told the master should be 12-14% of one of the callipers it is pushing. The persent of it being determined by the pedal length with the lever ratio
I want a good pedal feel for my car.
Help needed please


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## lukey-babes (Apr 2, 2009)

Sorry im used to writing on the vw golf forums.
so all that im talking about is golfs lol


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## GTijoejoe (Oct 6, 2001)

*Re: Twin brake master cylinder sizes???? (lukey-babes)*

Sounds like you are on the right track, you can use two different size MC's, normally they are actually the same size, and the difference in pressure is adjusted by the balance bar... but it is going to depend on your overall piston area FR and RR. 
OF course as you noted, you don't want to run out of stroke.... so lever ratio and MC size is important. Brake systems are all about compromises, you can't have it all. 
What is your opinion on good pedal feeling? Feeling will also come from your caliper stiffness.... 
I do not have the piston sizes of the calipers, can't help you out there.


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## lukey-babes (Apr 2, 2009)

Im either going to do .625 for rears and .750 for the fronts with a bias valve on the rear brake line.
But ive been told that .750 will give a realy hard pedal and would be overkill
So might just do .625 for front and rear.
Also been told a stock g60 master cylinder is 22mm so 2x .625 should be enough for all brakes.
Going to be using wilwood master cylinders and bia valve. (cant afford the callipers yet) lol
Dont think i would be running out of stroke with those on single piston callipers.
Right i think that sorted.
Too ebay lol


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## GTijoejoe (Oct 6, 2001)

*Re: (lukey-babes)*

Stiff pedals come from large MC. 0.75" is smaller than 22mm, therefore the pedal stiffness should be less......
When using a pedal box with no booster, the MC size is normally decreased, because you do not have boost assist anymore. To obtain more line pressure with same pedal effort you must decrease the MC size. 
Sometimes of course this effort can be balanced out with a large pedal ratio, but of course, you may know larger pedal ratio's also require high pedal strokes.....just like smaller MC's require longer strokes to displace more fluid volume..... 
System is full of balance to obtain your goal.
I would use 0.75" MC


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## lukey-babes (Apr 2, 2009)

*Re: (GTijoejoe)*

Yeah but im using 2 master cylinders and 2 of the .625s area will be more than 22mm master cylinders area.
And since i cant find any smaller than that i think im going to go with those.


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## GTijoejoe (Oct 6, 2001)

*Re: (lukey-babes)*


_Quote, originally posted by *lukey-babes* »_Yeah but im using 2 master cylinders and 2 of the .625s area will be more than 22mm master cylinders area.
And since i cant find any smaller than that i think im going to go with those.

Be sure to remember that it is not 2x the size because you are using two seperate MC's. Your single MC is actually a tandem, meaning there are two MC's bores with one input rod, this is to save space, they are stacked together
For example: 1" Tandem MC = 1" FR MC and 1" RR MC......


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