25.4mm master cylinder upgrade.

[VR6 Gar 10]

There is a thread on ED38 at the moment in which Rubjonny mentions you can use a T4 transporter 25.4mm MC as a direct replacement in our cars.

Anyone done this or even aware of it?

My brake pedal isn't the best thanks to the 6 pots so considering it as they can be had for only £39 from VW Heritage (5% discount if your an ED38 member)

Part number is 7D0611019A

[STU175 0]

i have heard this also.

i will be trying it when i fit my twin piston audi s2 calipers, hopefully works LOL

[GrahamU 5]

How many outlets do they have?

 

The old Audi 100's (and s2's IIRC) also used to have a 25.5mm MC that could be fitted to our servo's

[VR6 Gar 10]

How many outlets do they have?

 

 

4.

Edited February 22, 2014 by VR6 Gar

[GrahamU 5]

shame, was hoping you'd say 3...

 

On mine, the fourth that is not threaded I have shaved back so the cam belt cover of the 1.8t doesn't hit it.

 

Good to know though.

[VR6 Gar 10]

Just come across a thread that says the 25.4mm one is too big. Pedal too firm with next to no travel. 23.8mm one sounds a better option.

[STU175 0]

it makes a difference if you have abs or not to which you need. ive only really researched non abs

check out this link it gives some useful info and photos

http://www.myturbodiesel.com/1000q/a3b4/girling-g60-brake-caliper-swap.htm

ive allready bought the transporter one so i'll find out soon!

[J.C 10]

I'll be following this with interest as my pedals a bit low after fitting 288's,

I did read somewhere that if you have a siezed rear caliper slider then the hydraulic pressure causes flex in the carrier causing a low pedal, they say this can be checked by seeing if the rear pads are worn in a "wedge" shape

[VAG-hag 0]

Ill be watching this thread with interest!

[Dude VR6 0]

On race cars, the smaller the diameter the bore of the master cylinders, the stiffer the pedal, but the greater effort required. So if you require a stiffer pedal, get a master cylinder that's smaller that the OEM one.

[VR6 Gar 10]

On race cars, the smaller the diameter the bore of the master cylinders, the stiffer the pedal, but the greater effort required. So if you require a stiffer pedal, get a master cylinder that's smaller that the OEM one.

By reducing the MC size you are reducing the amount of fluid moved by the pedal stroke which in turn increases the amount you have to push it to have the same braking effect.

This is why you increase the MC size after fitting brakes with bigger pistons. If you decreased the size of MC you wouldn't be moving enough fluid to properly apply the brakes.

 

EDIT. I think what you are talking about is the servo, not the MC.

[GrahamU 5]

On race cars, the smaller the diameter the bore of the master cylinders, the stiffer the pedal, but the greater effort required. So if you require a stiffer pedal, get a master cylinder that's smaller that the OEM one.

 

 

I was thinking of questioning this but I see your in Banbury and are talking about race cars so I assume you work for a team?

[jezzaG60 0]

A bigger m/c will give less pedal travel to move a given amount of fluid, the trade off is that more pedal pressure will be required to give the same braking force. Pressure = force/area. People seem to have created some internet myth that bigger is better when it comes to sizing a master cylinder, you want it just big enough to give a sensible pedal travel.

I have run my corrado with both wildwood and Brembo 4 pots and mk4 rears on a standard master cylinder. With new discs and pads, braided hoses and the brakes properly bled there is no issue with excessive pedal travel.

[VR6 Gar 10]

I stand corrected on the force side of things, but obviously my point about feel/firmness stands.

I run Wilwood 6 pots with mk4 rears, braided lines, new rear pads and new front pads and disks and pedal travel isn't too bad but could be better.

However if changing the MC for a bigger one will increase how hard I have to apply the pedal I think I will just deal with it.

[fla 9]

Gar, if you change the point on the brake pedal where the mc piston rod attaches, ie nearer to the fulcrum will make it easier to press, less force required but will also need more movement. So i guess if you use a bigger mc and move the attachment point up you'd get stronger braking, less effort and good feel. But its a bit trial-and-error. It could be worked out though using turning moments.

[Dude VR6 0]

I was thinking of questioning this but I see your in Banbury and are talking about race cars so I assume you work for a team?

 

Yes I do work for a motor racing team, have been working in Motorsport for the last twenty years