gsxrken

BTW, 67Mustang302, you make a ton of sense on this thread. The knee point on the prop valve is a nice street addition.
http://docs.google.com/viewer?a=v&q=...KUx9a4dlQm0r1Q

.boB

I also have Wilwood brakes; 6 piston in front, and 4 piston in back. I'm using the same MC set up - 3/4" front and rear, with a 6:1 manual pedal. Bias is decididly to the front.

I find braking performance and balance to be outstanding. I can out brake most corvettes in my race group.

I expect your 1" MC is for the front?

If you do a web search, you can find formulas to calculate caliper pressure.

The bigger the MC is, the more volume it moves. The down side, it takes a lot more pedal pressure to create the same caliper pressure. I'm thinkning your 1" MC is too big. At most, I'd go 7/8" in the front. Since the bias needs to be to the front, Switch MC's front to rear. Put the 3/4 on the front, and you'll get a lot more pressure, but slightly more pedal throw. If you like it, buy another 3/4" MC.

gsxrken

Bob, glad to hear it you got it dialed. I do have the 1" to the rear and the 3/4 to the front. What pad compound are you running? I had Q pads (horrible) and currently have E pads).

Sorry for the hijack- I don't see a private message function on this web forum. ???

.boB

I'm using a BP-20's on th street. Good compromise with low dust, quiet, and good performance when cold. I started with BP-10's, and I like these a lot better.

For the track I switch to polymatrix A pads. Very agressive, kinda noisy, and make a fair (but not a lot) of dust. Wow, that's an awesome track pad. The car will almost stand on it's nose lap after lap. I love this pad.

moonmr

Looks like the CNC set-up uses a sleeve that is longer than any aftermarket set. The sleeve needs to be 1" or less in length in order to have the same adjustment as an aftermarket pedal such as Wilwood, Tilton or Coleman.

If you will measure the sleeve length on any of these pedals you will see that it is 1" long.

You were sold the wrong size master cylinder should be using 3/4" for front and back.

gsxrken

Thank you for your reply. Can you explain what you mean by the "sleeve"? Is it on the balance bar?
I guess CNC got it wrong then- they asked me what I was running and then spec'd these two masters. Why do you propose that the 1' is too big? I was thinking that perhaps I am encountering hydraulic resistance from the 1" MC before I am properly stroking the 3/4?" one. Is that your thought as well or did you have a different reason?
Thanks again.

moonmr

Here is a the PDF file of a Wilwood brake pedal assembly that uses a balance bar.
http://wilwood.com/PDF/DataSheets/ds252.pdf
Look at page 3 Figure 2. The part inbetween the two (2) clevis' is the sleeve; inside the sleeve there is a sherical threaded ball that holds the threaded rod, which holds the clevis.

Whoever designed the CNC setup "COPIED" something without the knowledge of the engineering involved in making a part. ANYONE can COPY a part, unless you have the engineering background, the COPY CAT will not know the whys or the hows. CNC made the sleeve to long so that limits the motion of the threaded rod. Simple math/geometry.

The Gorilla Balance Bar Assembly is made correctly.

Here is a quote for this Thread as boosted on page 2.
[QUOTE] [FONT COLOR="BLUE"]Gorilla, "The advantage of the Dual Master cylinder is with a 3/4" bore the output pressure is 1400 psi and there is no wasted energy when using a balance bar. This this the part I have trouble explaining to you, because I do not have an Engineering degree so I can not explain it in the correct Physics Terminology. I would hope you engineers can jump right in and do it for me. This is a copy of a link from a brake article on the internet and I quote,
http://www.deanoshiro.com/brakes/bra...le.html#dualmc

........."There are major advantages to using dual master cylinders: (1) Smaller diameter master cylinders can be used to increase output pressure. The design allows the application of two master cylinders being applied at the same, thereby doubling the volume output. Because of this high pressure output you will not need a vacuum booster. If you are running any type of camshaft, chances are you do not have enough vacuum to run the booster anyway. (2) The balance bar eliminates the use of a proportional valve and gives you the optional remote adjustment. (3) The remote fill applications deletes the need for residual valve normally used when the reservoirs are lower than the calipers.

When calculating the output pressure of each master cylinder you can not say that applied pressure is “shared” equally between the two (2) master cylinders. If the two master cylinders did not have a balance bar between them and the application of force was always equally distributed this statement would be true. The balance bar allows the applied pressure to be distributed unequally.

Example:

6:1 ratio pedal assembly
¾" master cylinders
Applied force of 100 pounds with your foot

The formula shows that this combination produces 1359 psi, however if you apply the 100 pounds of force to both of them equally it will only produce 50 percent or 679.5 psi.

What the balance bar allows you to do is apply 65% of the force to the front and 35% to the rear so the actual output pressures would be 883 & 475 psi.

This is how you are able to obtain maximum braking with the same amount of applied force. When you are using a tandem master cylinder (OEM type inline bore) the output pressure is equal in both ports and the only way to reduce the pressure to the rear braking system is through metering (distribution block, combination valve or engineering in the master cylinder) or proportional valve. This works fine when you have more than enough pressure with a power booster but when you are using a manual master cylinder this energy is “wasted”.

The easiest way to test this "wasted energy" is to apply 100 uniform pounds of pressure to a 6:1 pedal ratio and measure the pressure at the front calipers and the rear calipers with a pressure gauge. You will find that you will not have 763 psi you will have a reduced amount directly related to your proportioning or reduced pressure in the rear. If you reduce the pressure in the rear by 15% the out pressure in the front system will only have 648 psi at the gauge. The 648 psi is not taking into account "Friction Lost". Friction Lost is the amount of pressure lost from length of travel and the size of the piping.

The only way to know the effective actual output pressure of your system with a proportional valve or distribution block installed is to measure it with a pressure gauge when using a Tandem MC setup. You get 100% when you do not have this restriction on dual master cylinders. So how many pounds are you actually pushing with your foot when you use a Tandem MC?[/FONT]

Norm Peterson

On just a quick scan,
"Friction Lost" only acts when the fluid is actually moving, and will also depend on the fluid velocity. Once your pads come up hard against the rotors, brake fluid velocity drops to essentially zero. Also dropping to almost zero is the flow resistance (your "friction lost").

What it does affect (slightly) would be the pressure in the wheel cylinders during the brief time that the pads are actually being moved to take up whatever running clearances exist.


Norm

moonmr

Yes, Norm you would be 100% correct. The lost in pressure would only apply briefly while the fluid is in motion. No lost once the motion is stopped.

SomeHumanBeing@Aol.com

Hello Vintage Mustang Brake guys, after reading this thread I'm almost afraid to jump into the water. What a long and scary debate. Okay, I'm running Dual Master Cylinders, on my wife's car to boot. I do ALL of my homework, and yes math, before making a decision. Especially on a subject like brakes, before handing the keys to a very fast vintage muscle car over to my wife or sister.
But, I selected dual master cylinders for one simple reason. Adjustability. The problem 67mustang302 mentioned, bias under low braking loads, is technically true. But, in point, somewhat secondary to the more important primary goal, STOPPING THE CAR AS QUICKLY AS POSSIBLE! When did we forget that that was the purpose of upgrading the brakes in the first place?
Gross front/rear bias is best accomplished by properly selecting of hydraulic components based on total weight and distribution. But, a balance bar system is pretty much the only way to FINE TUNE front/rear bias WITHOUT electronics. If you have a speed sensor behind each wheel, a fast microprocessor, a bunch of bypass solenoids and an accumulator then setting brake bias becomes a non-issue. Simply have the computer add or remove pressure as the variations in wheel speed indicate. In which case, the tandem vs balance bar debate is moot. Hence the continued use of tandem master cylinders in modern cars. But, unless someone feels like doing a HUGE amount of work, this isn't possible for us vintage car fans. So, we gotta work for it. Which shouldn't be a surprise to any of us.
Before the flaming begins, for those who care, after doing my homework, I settled on CNC dual master cylinders, with cable adjustable balance bar for my wife's 1967 Mustang. Using a 1971 Mustang disc brake spindles, I installed Wilwood 4-piston calipers all around. Differential bores in the front (1.88 1.75 for 5.18 total sqin) and but not the rear. The rear calipers use 4 identical 1.38 pistons. (4 x 1.38 = 3.00 sqin) The car has, 12.90 x 1.25 Coleman floating rotors all around. (The rear rotors being the same size as the front was done for convenience of repair, as that is the size I selected for the front. Factually speaking, it was unnecessary.)
The CNC mount really ended up being a starting point for dual
master cylinder on a collapsable steering column equipped car like my wife's.
Everything else was up to me. The caliper selection, rotor sizing and master cylinder sizing was selected by me based on my calculations. I factored weight of the car, it's distribution, it's spring rates, what conditions it's going to be used in, AND the advice of people who've done it before. (CNC's advice changed based on who I was talking too.) While I am fairly confident in my engineering abilities, it's nice to ask someone whose actually done it before, and listens. Anybody whose honest with themselves should be willing to admit, physics matter, more then anything else in point of fact, but don't ever assume YOU know best. Most of the advise and help that ended up working, came from Dean and HotRodsUsa, Yo Shigmasa of Contemporary Auto Machine, Craig Railsback of BDS, and Nick Christmen of Brake Hoses Unlimited.
Once I got the CNC made setup, it was immediately apparent that the balance bar tube was made wrong, and would not accept either pushrod I had. The stock Ford clip retained manual brake pushrod, or the SSBC's adjustable one I ordered. So, I was very frustrated by the fact that I just dropped $350 big ones and I still was forced to make a new tube just to hook up the brake pedal. Come on guys/gals, how hard is it to tap the damn tube for 3/8-24? While I was at it, for adjustability, I did shorten that tube to 1.600 from 2.125 as well. I also hard-anodized the bracket, as they should have, and hard-chromed my hand-made sleeve. (Basic common sense things engineers do for durability.) CNC inc, has a nice bracket, nice pinned threaded spherical rod ends, and a nice selection of master cylinders. But that's it, your on your own for the rest. Their attention to detail, and customer service frankly suck and conversations with them are unproductive at best. At any rate, my instincts told me I didn't need residual pressure valves, but they insisted I did. So, I bought them anyway, because I thought for sure they couldn't CAUSE trouble. But, I was under the impression from the photos they sent me that the residual pressure valves were an option that were installed INSIDE the damn master cylinders when you ordered them. I didn't realize they are a needlessly long sloppy addition to the front, making the already a bit unwieldy CNC setup, even bigger. So, I removed them with no change in pedal feel whatsoever. The car's pedal feel is similar to a "hard" modern power brake tandem master cylinder equipped car. Bias is of course adjustable from the cabin, so after a very short bit of instruction, my wife learned to change it based on traction conditions. And she does. When it rains, she takes about 20% out of the rear and adds it to the front.

BTW, for the record, dual, non-adjustable, master cylinders HAVE been used on street cars at one time or another by Lotus, Masarati, Triumph, Rolls Royce, BMW, Mercedes, Ferrari, Alfa Romeo, and I believe even Lincoln. All before microprocessor controlled ABS era of course. Additionally, for what it's worth: A balance bar system's pressure bias curve isn't static as was stated earlier, but is a fairly simple and predictable curve based on a ratio of load applied to the bar by the operator, and each of the master cylinder's piston area to caliper piston area ratios.