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Old 06-12-2006, 08:37 AM
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master cylinder volume vs pressure

Need a little clarification on this and I'll use my own example. My 41 pontiac has the original MC. Haven't pulled it yet, but it looks like a 7/8ths bore.
I would like to go with a dual reservoir system, if I can make it fit. A smaller diameter bore would give me more braking power, but how can I tell if it will move enough fluid? {that is, find out before I buy a new MC, plus core charge/fabricate a bracket/modify the push rod and replumb the lines?}
I understand the benefit of having residual valves in line to stop the system from draining back to the MC, but is there also an advantage to having the line full, so it takes less fluid to move the shoe? Can anyone tell me how to calculate the necessary amount, or have experience with an early GM change over? thanks, don

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Old 06-12-2006, 10:29 AM
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There is a formula that was in one of the HP books on brakes. I may have a copy of it.

Another thing to consider is the stroke of the master cylinder. They are not all the same. This will affect your pedal travel, more stoke more pedal movement.

I seem to remember the author adding the required capicity of the wheel cylinders and measuring the output of the master cylinder. From there he made sure the master cylingder could supply the demand plus some.
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Old 06-12-2006, 08:20 PM
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pressure vs volume

damn, hadn't even thought about that. smaller bore but longer stroke could give me more pressure and equal volume. hope you can find the formula.
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Old 06-13-2006, 10:13 AM
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Good general information
http://www.wilwood.com/Products/005-.../pedaltech.asp

I think this was the formula (second one down)
http://www.fortunecity.com/silversto...193/brakes.htm

I would think that if you have a working system you could calculate the volume of your existing MC and convert to a new bore to see what stroke you need to be the same volume?
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Old 06-16-2006, 10:47 AM
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volume versus pressure

That seems simple enough, if I take the whole system apart. Is there any place to look up these old specs? I went to a local parts wharehouse this week. they were very helpfull, but quite frankly, don't have what I need. No info on my existing system. Pictures of master cylinders with the bore, but not stroke. [Also could not find a single master cylinder below 1 " that they had in stock. Apparently, with power brakes they increased master cylinder bore to move more fluid to larger cylinders, especially discs. Early Bronco II cylinders are under 1", but already on the hard to find list.]
I will start pulling down the system this weekend to see exactly what I have, and look for places to improve it.
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Old 06-16-2006, 11:00 AM
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If you're converting to disc keep in mind that in '84 - '85 GM was changing their calipers to the quick takeup style, which retracted the pads away from the disc. These require the quick takeup MC to move them to the disc before the serious apply pressure came in. In effect, gave them an initial push to take up the slack. It was an economy move by GM to reduce drag while driving.

I beat myself to death using early '90's AstroVan calipers (boosted) on my fronts before I learned that. I could bleed my heart out, get pedal and as soon as I fired it up it went away (the pedal).
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Old 06-17-2006, 11:35 AM
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Also I think you will find that you shouldnt need residule valves unless your master cyl. is located below your brakes, like a frame mounted system. at least that is what i have run into.
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Old 06-22-2006, 03:39 PM
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You might look into the 79 Fox Mustang manual brake cylinder (7/8"). It is modern and the only Fox set up that has the fittings in inches dimensions. They are about $ 20.

You should consider an upgrade to better front brakes.
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Old 06-23-2006, 07:51 AM
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Try MP Brakes.com . they have alot of stuff and a great free catalog with a lot of information.
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Old 06-23-2006, 10:49 PM
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brake help

xentrix - hate to sound like a dumb a..., but what is a fox mustang?
or is that a fox brand, mustang master cylinder? there are a dozen listings for 79 mustang M/C's. I assume the non power model, but there is the Bendix D and bendix, not D, and apparently, non bendix. None of them with any specs. Can you recommend a site that gives bore and stroke with the master cylinders? thanks, don
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Old 06-25-2006, 09:19 PM
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Quote:
Originally Posted by oldguy829
xentrix - hate to sound like a dumb a..., but what is a fox mustang?
or is that a fox brand, mustang master cylinder? there are a dozen listings for 79 mustang M/C's. I assume the non power model, but there is the Bendix D and bendix, not D, and apparently, non bendix. None of them with any specs. Can you recommend a site that gives bore and stroke with the master cylinders? thanks, don

No problem, every one of us had to learn it sometime.

The 79-93 Mustangs are the "Fox" chassis and is shared with the Fairmont, Granada, and the Continental. Later cars are called the "SN95" until the new chassis that just came out.

In my experience the 79 manual brake cylinder usually only has one listing, and I think it is the only one with the line fittings in inches (not metric).

Sorry don't know a site.
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Old 06-28-2006, 11:18 AM
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For more information than you can stand, check out ECI brakes at ecihotrodbrakes.com

Generally, you don't have to knock yourself out figuring out the right combination...Detroit did that for us for free. Unless you are downright anal, you can't go wrong (for streetrods anyway) with early model Mustang MCs. They are engineered with built-in proportioning between front and back, and unless you mount the MC below the calipers and wheel cylinders, you don't need any residual valves. They have plenty of capacity for front disc and rear drum setups.

George
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Old 06-29-2006, 10:59 AM
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master cyl volume versus pressure

gdubstub. Good site with good info and some stuff I hadn't seen before. Nothing for Pontiacs, I called to disucss using Chevy stuff, but because of the "top hat" frame, it won't work on Pontiacs.
I don't try to be anal (just happens sometimes) but I don't see how detroit could have anticipated my 41 pontiac with a 350/350, chopped springs and dropped rear axel when they designed a master cylinder with built in proportioning valves? And yes, the M/C is frame mounted below the wheel cylinders (especially after the mods) so I need residual valves. I don't see any answer except to fabricate my own conversion bracket, offset the pushrod, and use a later model M/C. If i'm going to make the brakes better, I need to know bore and stroke (or volume) of the M/C, and when I ask that question I get a blank stare. Surely someone knows where this technical data is available?
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Old 06-29-2006, 05:33 PM
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Use one with the same bore size as your original. Check the bore size for sure first.
If you go smaller with more stroke, you might have too much travel in the pedal. That's the trade off for getting the same volume... more travel.
Drums don't need all that much effort, so same size should be fine. It was fine for Grandma.

A tandem master of the same bore as original should easily have sufficient volume for your drum brakes, especially provided you find one which lists for a vehicle with similar sized or larger wheel cylinders.
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Old 07-01-2006, 11:20 AM
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Quote:
Originally Posted by yesgo


If you go smaller with more stroke, you might have too much travel in the pedal. That's the trade off for getting the same volume... more travel.

especially provided you find one which lists for a vehicle
.......... or larger wheel cylinders.

Larger wheel cylinders/ smaller master cylinder..... the effect is the same.

Going from 1" to 7/8" MC adds about 1" pedal travel.
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