Master Cylinder with 256mm front disk upgrade

[juan27]

I've decided to do the brake upgrade Teflon Tom describes here:

http://www.briskoda.net/forums/topic/189146-felicia-256mm-vented-brakes-upgrade/

In short 60mm cylinder calipers with 256mm Hyundai/Kia vented disks

The rear drums will be left as standard, but I believe as my Felicia is an estate (kombi) it has the biggest 22.2mm rear wheel cylinders.

I've now sourced Granada calipers/carriers, 14" wheels and some new disks......but I'm pondering if I need to change the master cylinder. I've searched through the various threads here and the answer doesn't seem to be cut and dried.

I think Tom mentioned that the VW Sharan master cylinder was a direct fit upgrade, anyone had any experience with using this?

On the other hand maybe I just need to try it with the standard one if this still results in acceptable pedal travel.

Any thoughts?

[KenONeill]

The volume of a cylinder is given by pi()*R^2*H, or PI()*D^2/4*H.

R is the radius of the cylinder, in this case keep it in millimeters. H will be the stroke of the wheel cylinder, also im mm.

D is the diameter of the cylinder, which is what you have, so you need to move (2827mm^2*H*number of wheel cylinders) mm^3 of fluid to apply your brakes. Ih have no idea what H is, or what the piston size of your master cylinder or standard wheel cylinders are, so I've given you the theory, and will butt out.

[nu99et18]

I have a 23.8mm master cylinder in my felicia, its from an audi and fits with no modification. However its only has 2 outlets where as the felicia one is 4 ports so you will need 2 T pieces and some brake pipe.

Il try and find the part number for ya

[TeflonTom]

i use the standard non abs cylinder on mine and it works fine, just gives a slightly long pedal which i prefer, some people dont like the way it feels though.. all i'll say is that the relationship between master cylinder and caliper piston is very important so dont mess with it unless you fully understand the consequences of mismatched components

[juan27]

The volume of a cylinder is given by pi()*R^2*H, or PI()*D^2/4*H.

R is the radius of the cylinder, in this case keep it in millimeters. H will be the stroke of the wheel cylinder, also im mm.

D is the diameter of the cylinder, which is what you have, so you need to move (2827mm^2*H*number of wheel cylinders) mm^3 of fluid to apply your brakes. Ih have no idea what H is, or what the piston size of your master cylinder or standard wheel cylinders are, so I've given you the theory, and will butt out.

I think its fair to say pedal travel will increase....

Edited 27 March, 2013 by juan27

[juan27]

i use the standard non abs cylinder on mine and it works fine, just gives a slightly long pedal which i prefer, some people dont like the way it feels though.. all i'll say is that the relationship between master cylinder and caliper piston is very important so dont mess with it unless you fully understand the consequences of mismatched components

Point taken. I certainly won't be experimenting lightly with anything someone else hasn't tried and tested.

I guess I should have said at the top that you previously suggested the VW Sharan might provide an upgrade alternative before anyone does anything too daft.

Edited 27 March, 2013 by juan27

[nu99et18]

4A0611021D the part number for 23.8mm audi master cylinder.

I only upgraded mine as i did rear disc conversion aswell as the 256mm front upgrade

[juan27]

I have a 23.8mm master cylinder in my felicia, its from an audi and fits with no modification. However its only has 2 outlets where as the felicia one is 4 ports so you will need 2 T pieces and some brake pipe.

Il try and find the part number for ya

Thanks I appreciate that.

[TeflonTom]

the other improvement you can make to the braking system is taking the rear axle bias valve out (if you have one) and changing the rear brake pipes to suit, then use the screw in proportioning valves in master cylinder like you get on the abs models.. i found that on a lowered wagon it would have strange effects to the rear brake bias coming on and off load when cornering hard

[TeflonTom]

4A0611021D the part number for 23.8mm audi master cylinder.

I only upgraded mine as i did rear disc conversion aswell as the 256mm front upgrade

on my 1,8T car i'm running with the standard oem non abs master cylinder and servo using ford mondeo v6 60mm piston calipers on the front on 280mm discs, and using mk3 golf vr6 rear calipers with 38mm pistons on 232mm discs on the back and it works perfectly, like i said before the brake pedal travel is a little bit on the long side but i like it that way, i've removed the rear bias valve and used the abs type load sensing valves on the master cylinder for the rear brake circuits, having longer brake pedal travel gives awesome stopping power because there is much more clamping force on the discs, the rear brakes barely do anything at all

[nu99et18]

on my 1,8T car i'm running with the standard oem non abs master cylinder and servo using ford mondeo v6 60mm piston calipers on the front on 280mm discs, and using mk3 golf vr6 rear calipers with 38mm pistons on 232mm discs on the back and it works perfectly, like i said before the brake pedal travel is a little bit on the long side but i like it that way, i've removed the rear bias valve and used the abs type load sensing valves on the master cylinder for the rear brake circuits, having longer brake pedal travel gives awesome stopping power because there is much more clamping force on the discs, the rear brakes barely do anything at all

Yeah i have piped past the rear bias valve and fitted an adjustable valve up front by the master cylinder and im really pleased with how they turned out, great brakes and a with a strong pedal.

N i only did the rear disc swap as a little project and the fact they look better than drums lol

Edited 27 March, 2013 by nu99et18

[uma1998]

i have all the parts to do this mondeo calipers golf mk3 rear disk set up so can i just bolt them on or do i need to change master cylinder... and i have the hole abs set up as donnor car i used had abs and i really want to get car back on road as mot run out and rear breaks are gone...

[juan27]

i have all the parts to do this mondeo calipers golf mk3 rear disk set up so can i just bolt them on or do i need to change master cylinder... and i have the hole abs set up as donnor car i used had abs and i really want to get car back on road as mot run out and rear breaks are gone...

From past threads I thought the front brake upgrade was incompatible with ABS, but I could be wrong. Would be interested if it can be made to work with ABS?

[KenONeill]

the other improvement you can make to the braking system is taking the rear axle bias valve out (if you have one) and changing the rear brake pipes to suit, then use the screw in proportioning valves in master cylinder like you get on the abs models.. i found that on a lowered wagon it would have strange effects to the rear brake bias coming on and off load when cornering hard

It would do; here's the science (well engineering) bit.

The load proportioning function on the standard pickup (and van) works on ride level, and assumes that the lower the ride height the higher the payload, and hence the more force can be applied to the rear brakes before they lock. Reset the ride height (either deliberately with lowering springs or accidentally with weak ones) and it assumes you've got a load on and puts more effort to the rear brakes. You might be able to reset this by modifying the bell crank, but engineering around it like Tom describes is more certain.

Edited 8 April, 2013 by KenONeill

[TeflonTom]

that's dead right ken, it does in fact have an adjustable crank lever, it's done by slackening a nut and bolt and sliding it up or down then re-tightening it in a different position so that is the same relative to the original ride height, hope that makes sense.. i dont think i have any pictures of the rear bias valve that will be of any use to show on here sadly.

what i will say to anybody attempting it is this, if you do decide to take it out of the braking circuit like i did please make sure you are 100% sure you know what you are doing, and also bear in mind that a 15 year old brake pipe often snaps off when you try to undo the unions so make sure you either have a replacement pipe to hand or at least the equipment to make a new one otherwise you could get stranded with an unusable vehicle, brakes are safety critical folks

[KenONeill]

Ok, from what Tom says, you can reset the stock proportioning valve to suit a lowered ride height as follows:-

1. With the empty vehicle on its wheels, measure the angle the bellcrank makes to the horizontal carefully using a real protractor.
   
2. Note this number down and don't lose it.
   
3. Fit your new suspension.
   
4. Go for a gentle run to settle everything.
   
5. Loosen the bellcrank bolt and adjust the angle back to the value you got in (1).
   

[rolo]

Found that just doing the conversions to 256 & 300mm discs (ford calipers) front and vw mk2 discs/mk3 calipers rear works good without making it complicated

Edited 17 April, 2013 by rolo

[juan27]

Found that just doing the conversions to 256 & 300mm discs (ford calipers) front and vw mk2 discs/mk3 calipers rear works good without making it complicated

So are you saying that setup works well with the standard master cylinder? If so I should be fine just doing the fronts I think from a pedal travel point of view.

Also what's the this about 300mm discs? What caliper fits those and what car are the discs from? Presumably they need huge wheels?

[TeflonTom]

Yeah there is a Renault disc that is 300mm I believe, but you need to get the centre bore machine to 62mm to suit the skoda hub, and it will be mk3 mondeo calipers. You would probably need 16" wheels.

yes it does work fine using the standard master cylinder with the 260mm mondeo or sierra setups (using 256mm discs), like I said earlier I've used the standard master cylinder on my 20v engined car and it's fine even with a rear disc brake conversion too, I can pretty much guarantee mine is faster than pretty much any other felicia in the uk, I don't understand all this talk of it not being adequate for people??

[juan27]

Yeah there is a Renault disc that is 300mm I believe, but you need to get the centre bore machine to 62mm to suit the skoda hub, and it will be mk3 mondeo calipers. You would probably need 16" wheels.

yes it does work fine using the standard master cylinder with the 260mm mondeo or sierra setups (using 256mm discs), like I said earlier I've used the standard master cylinder on my 20v engined car and it's fine even with a rear disc brake conversion too, I can pretty much guarantee mine is faster than pretty much any other felicia in the uk, I don't understand all this talk of it not being adequate for people??

Standard master cyl for me Tom all the way. I am fully convinced.