# problem with master cylinder 25.4mm on golf mk2



## phildar29 (May 5, 2008)

hello everyone ,i'm french and i have a question

on my golf mk2 i have adapt brakes from golf 3 vr6 and with a master cylinder 22mm no problem all it's ok ,but last week i have fitt a master cylinder from t4 bus 25.4mm ,now it's special i have to push at the maximum of the pedal to brake ,now my brakes pedal is to long!! idealy i have to modify the axle of brake pedal to adapt the movement but i don't want to do that!
can i adapt another pedal? someone have asolution?
thanks


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## diagnosticator (Aug 27, 2005)

If the T4 master cylinder does not work correctly with the brakes on your MKII, why do you want to use it? Clearly, using the original master cylinder works good, so reinstalling the correct MKII MC is the technically correct fix for the existing increased pedal effort and reduced pedal travel, right? The reason the larger T4 25.4mm master cylinder causes the problems you described, is because the volume of brake fluid displaced by the T4 master cylinder is higher than the volume of brake fluid displaced by the MKII 22mm master cylinder for the equivalent stroke distance of the brake pedal. So, the brakes are activated faster, by less brake pedal travel compared to the original MKII 22mm master cylinder. The associated effect of the larger master cylinder besides reduced pedal travel, is that the hydraulic "lever" ratio is now lower compared to the 22mm master cylinder, so higher pedal pressure is required for the same hydraulic pressure at the brake calipers, resulting in less braking power for the same pedal pressure. This is why the T4 master cylinder requires more pedal pressure and has reduced pedal travel compared to the MKII master cylinder.
Otherwise, the only practical way to increase the pedal travel, and the (lever ratio) braking power, is to use calipers with more piston area. Realize too, that the original MKII brake booster will not be sized to provide enough power assist factor with larger MC/SC hydraulic piston areas.


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## franciscomk3 (Feb 27, 2012)

^hes not having a rock hard pedal.
he has no pressure at all



air in your lines.
keep bleeding the brakes. look up "bench bleeding"


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## diagnosticator (Aug 27, 2005)

franciscomk3 said:


> ^hes not having a rock hard pedal.
> he has no pressure at all
> 
> 
> ...


 Thanks for the clarification.


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## 16valvulasturbo (Dec 1, 2012)

to diagnosticator: 

if i put a 25.4 MC in a originally equipped 22MC car; that creates the closer ratio of pedal effort. i understand that part. 
but now if i also fit dual piston caliper front brakes from an audi car; they require more flow of fluid to move the same distance as a single piston? will that help bring the pedal " feel" to the original 22MC set-up?


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## denongt (Jun 20, 2009)

i did the some in my corrado and i have the some problem..... what to do ?


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## diagnosticator (Aug 27, 2005)

16valvulasturbo said:


> to diagnosticator:
> 
> if i put a 25.4 MC in a originally equipped 22MC car; that creates the closer ratio of pedal effort. i understand that part.
> but now if i also fit dual piston caliper front brakes from an audi car; they require more flow of fluid to move the same distance as a single piston? will that help bring the pedal " feel" to the original 22MC set-up?


 
I typed up an answer twice only to back page by mistake, and lost the text. I will re type the reply when I am not so angry.


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## franciscomk3 (Feb 27, 2012)

16valvulasturbo said:


> to diagnosticator:
> 
> if i put a 25.4 MC in a originally equipped 22MC car; that creates the closer ratio of pedal effort. i understand that part.
> but now if i also fit dual piston caliper front brakes from an audi car; they require more flow of fluid to move the same distance as a single piston? will that help bring the pedal " feel" to the original 22MC set-up?



it dependss... lol

theres a lot of math involved and lots of needed info if you want an exact answer like...

piston sizes, booster type, force etc etc 

but for an estimate...
did the 25.4 mc come from the same car as the dual piston calipers you speak of? if yes. then the answer to your question is yes lol


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