# Brake System Design



## 20valveDriver (May 30, 2003)

Okay, all you closet engineers out there...
I'm designing a braking system for a car. It doesn't matter what car, really, but it's an '84 Scirocco. What I want are absolutely huge (okay, maybe just large) brakes to fit on this 2000 pound car. I was hoping to get 11" front and rear.
My question relates to the relationship between brake booster size, master cylinder size, and stopping power. Is bigger always better?
If I have a large master cylinder and smallish calipers, can the master cylinder be too big to the point where I lose braking feel?
Constructive comments, please!
-Tom


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## machschnelGTI (Jun 28, 2004)

*Re: Brake System Design (20valveDriver)*

If the master is too big for the system, you will experience an extremely hard pedal with absolutely no stopping power. You should use the same size master from the car with which the calipers came from. The booster doesn't matter so long as the booster pushrod mates correctly with the master cylinder piston.


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## 20valveDriver (May 30, 2003)

*Re: Brake System Design (machschnelGTI)*

Thanks for the info, Machschnel. Now let's get specific...
Is there a parts list out there for swapping big brakes onto an A1? So far I have the following:
Master Cylinder: Audi 4000, Coupe, or VW Quantum
Poportioning Valve: Any 4-disc VW/Audi, or same as above
Front Brake Carriers: Scirocco 16V, Audi 4000, VW Quantum, etc.
Front Brake Calipers: Girling "G54" Dual Piston from Audi 
Front Brake Rotors: 11" from G60 or 10.9" from Audi Quattro
Rear Brake Spindles: Mk2 Golf
Rear Brake Calipers: Girling "G60" single piston from VW G60, Audi 5000 on custom brakets
Rear Brake Rotors: ??? 11", baby!
Lines: ??? Stainless something or other... w/ Tilton adjustable prop valve for rears.
Help a brother out by completing the list!
-Tom


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## EUROROC (Mar 30, 2002)

*Re: Brake System Design (20valveDriver)*


_Quote, originally posted by *20valveDriver* »_Master Cylinder: Audi 4000, Coupe, or VW Quantum

What size MC are you planning on using... different audi's have different MC... 21mm, 22mm, 23.5mm, etc? Some Audi's only have 3 spigots on the MC so beware.


_Quote, originally posted by *20valveDriver* »_Front Brake Carriers: Scirocco 16V, Audi 4000, VW Quantum, etc. 

Not all audi and VW parts are interchangable... just a note.

_Quote, originally posted by *20valveDriver* »_Front Brake Calipers: Girling "G54" Dual Piston from Audi 

Dual Piston calipers were "Girling 60"

_Quote, originally posted by *20valveDriver* »_Rear Brake Spindles: Mk2 Golf 

What's the reason for this??? mkI spindles are the same...


_Quote, originally posted by *20valveDriver* »_Rear Brake Calipers: Girling "G60" single piston from VW G60, Audi 5000 on custom brakets


I have no idea what you are saying here... Girling "G60"??? do you mean corrodo G60 calipers? Remember Girling 60's (not Girling G60) are dual piston calipers. Don't bother with audi calipers in back... you can use mkIII calipers... much lighter than the first gen calipers used on the scirocco and GTI.

_Quote, originally posted by *20valveDriver* »_Rear Brake Rotors: ??? 11", baby! 

How much do you know about machining and metal... making a strong, lite and safe bracket is important. Also 11" rotors on the back require a great deal of work and parts from germany, etc. remember we're 4 lug 4x100 so larger rotors are not easy to come by.

_Quote, originally posted by *20valveDriver* »_Lines: ??? Stainless something or other... w/ Tilton adjustable prop valve for rears.

Wilwood also has an adjutable prop.. check it out. 
This is a huge undertaking... trust me I've been working on somthing similar for about 6-8 months and am only now ready to start spending $$$... Most of the parts I need for the rear have already been modeled and the front is still on paper but will get modeled as soon as I make the final decision on the calipers but recently I think I found a few new ways to make the system safer and cheaper. To me brakes are too important to take chances on... 
I'm not going to go into the specifications for the brake system I'm planning but I do have a couple of sets of Girling 60's laying around so if your interested let me know.
-Raffi



_Modified by EUROROC at 12:39 AM 9-2-2004_


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## rocco_luvr (Jun 12, 2004)

*Re: Brake System Design (20valveDriver)*

Why would you need 11" brakes in a 2000lb car? Wouldn't the friction between the brake pads and the rotors frequently overcome the friction between the tires and the road causing you to skid?


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## 20valveDriver (May 30, 2003)

*Re: Brake System Design (EUROROC)*

Raffi-
Thanks for the feedback! What are you going to mount your system on? This is a new idea, so please excuse the rough sketch posted above. I'll try to answer all questions.
It sounds like most of the parts I"m looking for (MC, calipers front and rear) can be sourced from an Audi 5000QT or Quattro Coupe. The Girling 60 calipers are preferred. I had the 54 and 60 confused earlier. The Audi also has the 23.2mm MC if I'm not mistaken.
The carriers from the Scirocco 16V, Audi 4000, and VW Quantum were all the same.
I'm using Mk2 rear spindles because my stock 8V brake setup was drum and I had the Mk2's laying around.
Thanks for the tip on the Mk3 rear calipers... Should be much easier to find and lightness is good! Also lets me retain a cable e-brake, but more on that later.
Rear rotors are still up in the air, too. I'd like to get the biggest rotor I can get. The car will be a rally/rallycross/street car, so the rear brakes are important. I may settle for a Mk3 or Quattro Coupe or other 4-lug rear rotor.
The design and machine work for custom brackets is no problem. I work in the automotive industry.
I was also checking out prop valves. In order to use any manually adjustable valve I would have to replumb the brake lines. This is a long way from interesting to me, but probably not so much as trying to get a self-adjusting valve retrofitted to the Mk1 rear beam. I'm up in the air on this one.
To be honest, if I'm going to replumb the system I may just suck it up and stick Wilwoods on all four corners. I wonder if the Audi 3-spigot MC you speak of is 2 front channels and 1 rear... That would help the plumbing for a manually adjustable prop valve.
Anyway, looks like the list has become this:
Master Cylinder: 23.2mm from Audi 5000QT or Quattro Coupe
Poportioning Valve: Any 4-disc VW/Audi w/ 23.2mm MC, or same as above
Front Brake Carriers: Scirocco 16V, Audi 4000, VW Quantum, etc.
Front Brake Calipers: Girling 60 Dual Piston from, well, whatever.
Front Brake Rotors: 11" from G60 
Rear Brake Spindles: Mk2 Golf
Rear Brake Calipers: Golf Mk3 on custom brackets
Rear Brake Rotors: ??? bigger is always better...
Lines: ??? Stainless something or other... w/ adjustable prop valve for rears.

More comments? Anyone?
-T


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## 20valveDriver (May 30, 2003)

*Re: Brake System Design (rocco_luvr)*

Raffi-
Nevermind my question in the earlier post. I just saw your "16 project" under your username... Not too bright sometimes.








Rocco_Luvr-
You'd be surprised how much traction you can find on gravel with rally tires! http://****************.com/smile/emthup.gif 
-T


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## Jetta2dr (Feb 19, 2001)

*Re: Brake System Design (20valveDriver)*

Heres a few things for you to think about. Where are you going to find 11" _rear_ rotors with an integrated hub in 4x100? The R32 and 20th AE have 10" rear discs, but those are both 5x100 lug pattern. Also if you use mk3 rear calipers you're not going to get any more swept area than you would if you used the mk3 calipers on the 8.9" rotors they're supposed to go on. You could use bigger pads maybe, but the gains would still be minimal. Also concerning the brake lines; putting in new brake lines is going to be _minimal_ compaired to the rest of the work you're going to need to do to get this to work. And with equal size front and rear rotors the brake bias is going to be different than the stock proportioning valves are set at. Plus do you want some crusty old lines feeding whatever expensive calipers you get?
And as for gravel tires' traction, I can lock up my gti's just fine with the stock 9.4" front and 8.9" rear discs. And with decent pads and fluid they stand up just fine to real stage rallies. So heat dissipation isnt much of an issue either, especially for a rallycross/street car. 
VWR used 13.9" front and 10.4" rear discs with 6 piston front and 2 piston rear calipers and a 0.75" master cylinder in the mk3 kit car for tarmac rallies. For gravel (which you say you'll be running on) they used 11.6" front and 10.4" rear with 4 piston front calipers and 2 piston rear calipers along with a 0.75" master clyinder. 0.75" is 19mm, if my conversion is right. I dont have the mk2 vwms manual handy, but the brakes were smaller than that I'm sure. And in an a1 chassis the brake requirements would be smaller yet.
I'm sure you know of all the other drawbacks that large discs/calipers will cause too. Its more mass to turn so you'll accelerate slower. Plus you'll need to run larger wheels (15" at least) so the cost of gravel tires will go up vs a 14" or 13" wheel/tire combo. Also your gear ratios will be lengthened (due to larger wheel/tire diameter) so you'll effectively give yourself longer gearing. Which is bad especially for rally/rallycross where the proper gearing is one of the best things you can do for your car. You could take the money you would spend on these brakes and buy a 4.6 final drive and be loads faster than another similar car with a 3.6 (or whatever is stock) final drive and huge brakes.
Its up to you though. Hopefully I gave you a few things to think about. http://****************.com/smile/emthup.gif 


_Modified by Jetta2dr at 11:29 PM 9-1-2004_


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## talx (Apr 4, 2003)

*Re: Brake System Design (Jetta2dr)*

Can you get any better/bigger than this?








I think I have al the answers








and I think you could call this absolutely huge
























Ok this is a brembo 4 piston caliper with 12" discs kit for a seat Ibiza 1.8T it originally came as a standard set up on the Ibiza CUPRA R and can be purchased threw VW dealership comes with 2 a set of calipers discs caliper mounts and brake hoses 
I have a set of mounts that are originally to fit G60 calipers on 16V scirocco bearing housing now a Ibiza has the exact same wheel bearing housing as a golf mk2 and the regular 1.8T Ibiza modal comes with 280 discs and the same calipers as the golf G60 now the brembo kit comes with mounts to mount on to the Ibiza/mk2 wheel bearing housing which means all that is needed to be don is attach the BREMBO calipers with the two mounts and it all fit together very nicely this is what I did it al fits perfectly

































And this is my rear brakes they are to from an IBIZA CUPRA complete with calipers mounts discs wheel hub axel guards oil lines and mounting accessories 
The Ibiza has a 4 whole setup in the discs like the scirocco, the axle mounting holes are the same and it comes with mk4 aluminum calipers but the big advantage is it uses a wheel hub with the bearing mounted in theme and not the usual discs that act as a wheel hub as well 
this has two advantages first you do not need to take the bearings apart when you replace the discs and adjust the spacing when you mount theme and The axle looks much stronger as well secondly I was considering getting the BBM 9.4 or 11 disc conversion but I do not need to do this now since it uses wheel hubs you can just mount the front discs in the rear all I need to do is trim the caliper career to fit the width of the disc and fabricate mounts to mount the caliper farther away 
The fact that they have a hall sensor is grate as well and will help me a lot when I get my standalone management DTA that will have traction control as well 








My wheels are Lenso RS5 16" 7"J 38 ET I just love theme they are exactly what I wanted for my car








to clear the brembo caliper they will need a 2 c"m spacer that’s no problem for me i had all the fenders trimmed when I got the body job dun and test fitted the rim with a 225/16/40 tire and had theme do the clearance sow there would be 1- 2 c"m of space and stiff suspension should do the job
















My set up 
Master cylinder: 25mm AUDI
Front calipers: BREMBO 4 piston kit 
Rear calipers: IBIZA CUPRA
Mounting: g60 caliper upgrade mounts + BREMBO mounts
Proportioning Valve: g60
Lines front: BREMBO 
Lines rear: CUPRA+16v scirocco Stainless


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## 20valveDriver (May 30, 2003)

*Re: Brake System Design (Jetta2dr)*

Jetta2dr-
Thanks for the "real world" data. You're right, I should probably just draw the line at 9" rear discs and be done with it.
Talx-
Stop making me drool! The picture with the wheel mounted is tasty.
Where on Earth did you get that rear disc setup from the SEAT? What year, and is anyone out there who has them willing to ship to the US? Those are perfect because they separate the bearing from the rotor, a design I never understood in the first place. Excellent!
This is great feedback, guys. Keep it coming!
-Tom


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## 1.9..16vTurbo (Jan 25, 2004)

*Re: Brake System Design (20valveDriver)*

Here's what i just bought!!!








http://forums.vwvortex.com/zerothread?id=1391875
http://forums.vwvortex.com/zerothread?id=1391864


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