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FFCobra Craftsman
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Jim let's step back and talk about brake hydraulics. There is no such thing as one MC kicking in first and no such thing as one MC dominating. When the brakes are pressed, even if one pushrod were to hit it's MC first, there will be no pressure built in that MC. The balance shaft will just cock somewhat. Pressure will only start to build when both pushrods are in contact w/ the MC pistons. The length of the pushrods, MC to balance bar, is adjustable so that at max pedal pressure the balance shaft is roughly perpendicular to the pushrods. The reason this is needed is that w/ varying MC sizes, as well as varying caliper sizes, the MCs typically do not travel the same amount. So the pushrod lengths can be adjusted so that at rest, the balance shaft may not be perpendicular to the pushrods, but when pedal pressure is applied and the MCs move, the balance shaft will move toward being perpendicular.
Wilwood balance 3 by craig stuard, on Flickr
In the pic the green arrows point to the thread on the ends of the balance shaft. The amount of thread showing tells you which MC will get the most pressure from the pedal. More thread = more pressure.
Balance bar 2 by craig stuard, on Flickr
This shows what is inside the top of the pedal. The bearing is locked into position on the shaft by a jam nut on each side. The brass clevises are threaded. So, as the shaft is turned, it moves left or right through the clevises, and pulls the bearing with it. The bearing is free to slide within the top of the pedal. So the pedal pressure is applied more to the MC that the bearing has moved closer to. Since we can't see inside the pedal, we use the amount of threads exposed on the ends of the shaft to indicate where the bearing is.
There is a caution that needs to be checked. Think of the balance shaft in the pedal but not connected to any MCs. There is a limit to how much angle the shaft can be moved to before it binds against the inside bore of the pedal. We need to make sure this limit is not exceeded when the brakes are pushed. This is also why there is a spec for the amount of clearance needed at the red arrows in the first picture. This is also why many people bleed one front and one rear caliper at a time. Because if MC #1 has all the air removed it will only move so far. If MC #2 has a lot of air, when the pedal is pushed, MC #1 stops moving while the other keeps going UNTIL the angle binds the shaft and now both MCs stop. But the one w/ the excess air usually has not gone to it's full travel so all the air will not be pushed out of it.
 

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"Getting back to the shop I again looked over the stock balance bar setup. There is the issue of adjusting the length of the rod going from the master cylinder to the mount on the regular balance bar that controls which brakes kick in first."

If the balance bar is not bound up (un-free to rotate) it will automatically "balance" the pressure applied. Both master cylinders will experience the effort at the same time, subject to their link's distance from the pivot point.

" On mine the rod for the front brakes has more threads showing (makes the rod longer) indicating this master cylinder will be dominate in the braking. This setting may be strong enough that the bias dial can't make much of a difference."

The reason the rod to the front master is longer is the front brakes typically take more fluid volume. Unless the difference is too radical, front and rear systems will get the pressurized brake fluid at the same time. See the Wilwood link.

"I was sure there were instructions on how to setup the master cylinders but I can't find it on the factory five, ffcars or other websites. "
 

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Discussion Starter #23
Thanks for all the info. As I looked at the balance bar setup on the Wilwood link old memories came rolling back. I thought I had all that figured out during the build. It is almost impossible to get a good picture of my master cylinder/balance bar setup because 1/2 is under the fender lip. I started to draw a picture but the measurements below applied to the Wilwood correct setup match up with mine.

I did a comparison on the Wilwood example and my setup and they are almost identical. I pulled the Wilwood cockpit adjustor so I could see all the treads. About 3/8" of treads are showing for the front brakes and about 7/8" (both without nuts) for the back brakes. To me that would put emphasis on the rear brakes. At rest the balance bar is slightly angled as the rod from the back master cylinder is 1/4" shorter. When the brake pedal is depressed the balance bar is on an even plane.
 

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with the balance adjuster sheet you saw that indicated which way to turn it was front/rear, did that include the installation diagram? As far as I can tell the adjuster cable could possibly be installed on either side of the balance bar, making a "rear" adjustment actually go toward the front if installed on the opposite side of the balance bar.
 

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Discussion Starter #25
I don't remember about the installation instructions, too long ago. My connection was on the engine side because it could not have easily been made to the other side. The theory is that the side that has the most threads showing is getting the emphasis. Probably worth trying the opposite to see what the results are. I'll post the results of my experiment.
 

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FFCobra Craftsman
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Yes you can install the adjuster cable on either end. That would also change the knob turn direction. But either way, the balance shaft end displaying the most threads will have the bias adjusted toward that MC.
 
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Discussion Starter #27
The effort on working on my brakes is drawing to a close. The 2008 MK3.1 build has PBR dual piston calipers on the front and a single PBR GT piston on the rear. It has Wilwood .75 master cylinders. I've played around with the balance bar between the master cylinders for years now. I can't seem to get much of a change made. Recently I reset everything so the thread length on the rod through the proportioning unit are the same. This should be putting equal pressure on front and back. I also reset length of the master cylinder push rod threads so they are the same. From 40 mph I can do a panic stop and get pretty good stopping results with black marks from the front tires only. No pull right of left. Good.

I would not be against using different brake pads (now carbotech are pretty new) and/or maybe switching the back calipers from the single piston GT units provided by F5 on the kit to a dual caliper if the price was right. Other than that I think I'll call it good and focus on electric power steering. The line pressure at all calipers remains at 600 psi.

I appreciate all the comments and suggestions. I don't plan on ever racing the Cobra or doing any serious driving so I'm hoping it will stay with me as is. If anyone has any parting comments for me on this subject I'll all ears. Jim
 
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