# Wilwood pedal assembly and 3/4" master cylinders for brakes/clutch?



## G60Driver (Mar 6, 2002)

I've been thinking about putting a Wilwood pedal assembly in my rabbit project and was wondering what the brake gurus thought about it. I'd like to use the small, 3/4" master cylinders for front/rear brakes and clutch slave cyl. My rabbit has manual steering and I'll probably be keeping the small brakes 9.4" but at the most upgrading to 10.1" brakes. Can I get away with running these small, totally manual brake master cylinders reliably and without killing myself? What would the pros/cons be of this setup? The main reason I want to run it is to get rid of the huge brake booster and clean up the engine bay, but I want decent brakes too. I don't mind spending the time to get them adjusted correctly (front to rear bias) but I want them to be safe.
Opinions?
These are master cylinders I'm talking about:








This is the pedal assembly:


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## G60Driver (Mar 6, 2002)

*Re: Wilwood pedal assembly and 3/4" master cylinders for brakes/clutch? (G60Driver)*

One more question, how would I rig up brake lights to this setup? Just fabricate a bracket to hold a brake light switch in front of the pedal?


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## Mortal_Wombat (Jan 29, 2004)

*FV-QR*

you could do what the older american cars did and run a brake pressure switch for the brake lights


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## GTijoejoe (Oct 6, 2001)

*Re: Wilwood pedal assembly and 3/4" master cylinders for brakes/clutch? (G60Driver)*

Of course with no booster, there is no boost asisst, so the only way to countermeasure pedal effort is pedal ratio and balancing MC size with stroke. 
The larger the pedal ratio the larger the stroke
The smaller the MC the more brake pressure with same or less effort.
The smaller the MC, the smaller the fluid displacement, the longer the stroke.
The larger the MC, less brake pressure with same effort, the shorter the stroke.
This is what you will generally balance with sizing a brake system pedal/MC combo. 
0.75" = 19mm
10.1" brake spec uses 22mm MC (i think)
My point: You need to also compare the piston sizes vs the two brake specs to understand MC size and fluid displacement.
Worst case, you undersize your MC and have large pedal ratio and you do not have enough stroke before you reach the floor/firewall before full brake apply.
In this case it maybe best to use a larger MC, but it all depends on all the specs of all the components. Perhaps you can consult with Willwood directly to help you sort your setup.
It sounds like a good idea to me, in addition to ^^^ you can use a inline pressure sender for brake lights, no need for a stroke switch. http://****************.com/smile/emthup.gif 
Hope that helps


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## G60Driver (Mar 6, 2002)

*Re: Wilwood pedal assembly and 3/4" master cylinders for brakes/clutch? (GTijoejoe)*

Now THIS is the kind of info I was hoping to get! Thanks GTijoejoe! http://****************.com/smile/emthup.gif
I can also buy Wilwood 1" master cylinders which equate to approx. 25mm. BUT, since the stock 10.1 brakes use a single master cyl (22mm) for all four brakes would I need to divide that by two to keep stock proportion? Also, how much extra help is the brake booster adding? I'll be using two separate masters (one front and one rear) and that's why I figured the 3/4" would be fine, or even overkill. In my calculation that would equal 19mm x2 (or equal to 38mm divided between all four brakes.) The math may not work that way when it comes to braking. I have no idea. That's why I'm asking here!


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## G60Driver (Mar 6, 2002)

*Re: Wilwood pedal assembly and 3/4" master cylinders for brakes/clutch? (G60Driver)*

Just got this response to an IM from Wackywabbitracer. I'm including it here so I don't loose the info:
"I ran dual Tilton master cylinders, 5/8 inch diameter, in the old WackyWabbit SCCA racer. I spent about two weeks engineering a "single Wilwood brake pedal" assembly into the car due to the conflicts under the dash area. I kept the clutch cable but had to use the original factory brake pedal for a clutch pedal with a lot of fabrication. The firewall area had to be reinforced due to the stress of manual brakes. I also used a Wilwood rear brake proportional valve to set the rear brake bias to keep the rear wheels from locking under braking. Cheers, Ryan."


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## GTijoejoe (Oct 6, 2001)

*Re: Wilwood pedal assembly and 3/4" master cylinders for brakes/clutch? (G60Driver)*

With respect to Wacky... you should understand the size of the brakes he was using, (piston diameters FR and RR), 5/8" sounds like good experience. Of course he's right about the firewall stiffness. Because of different pedals and placement there is different loading, over the structure. The shape of the firewall adds stiffness and support as needed for the original layout and input levels.
A booster's affect can be of ratios 2-4ish:1 (i think, there could be higher), normal is around 3ish, but either way you see my point, the can basically serverly decrease your pedal effort, along with a pedal ratio. 
I don't totally understand your mathematical logic...but....
Normaly now a days for OEM applications MC's have 2 bores in one unit (Tandem)) so if it is 19mm for both bores (they can be different sizes), you'll match 2 seperate 19mm MC's for the new pedal assy', or what ever the difference.



_Modified by GTijoejoe at 12:22 AM 5-23-2009_


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