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Re: Brake bias and caliper BORE size.
[Re: Kern Dog]
#1233108
05/17/12 04:58 PM
05/17/12 04:58 PM
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Joined: Jan 2003
Posts: 28,067
Irving, TX
feets
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Senior Management
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Posts: 28,067
Irving, TX
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The piston movement is easy to figure. You look at the bore of the master cylinder and the bore of the caliper pistons. Divide the master cylinder bore by the caliper piston bore. Take that total and divide by two since you have calipers on the left and right. Figuring one inch of movement is easy. Multiply the area by 1. Can't get much easier than that.  At one inches of depth your master cylinder holds .6901 cubic inches of fluid. The calipers have 5.94 square inches of surface area. You have two of them for a total of 11.88 square inches. Take a pan with an area of 11.88 square inches and drop in .69 cubic inches of water. How deep do you think it's going to be?
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Brake bias and caliper BORE size.
[Re: feets]
#1233109
05/17/12 05:33 PM
05/17/12 05:33 PM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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yup.
When calculating pressure or force generated at the caliper, that's a 2 dimensional calculation. area of master cylinder vs area of caliper pistons.
when calculating pad movement, that's a 3 dimensional calculation, master cylinder piston area times height (or stroke) vs caliper piston area times height/stroke.
as an example, I just had a rotor that was .030 out of round. that means as it rotated, it would push the pad and pistons back into the caliper. .030 of movement ends up being .060 of total displacement, because both the outter pistons would push in .030, and the inner pistons would also push in .030.
the guy I got the rotor from tried to tell me that my soft pedal that would pump up solid was not because of his out of round rotor, and that I had other problems (but agreed to send me another rotor anyway) I then pointed out to him that with a combined piston area of 7.76 in just one caliper, that I needed several inches of stroke out of the master with just 1" of area just to push the pads back out a combined distance of .060.
yes, when calculating pressures, you only use 2 pistons of the 4, because they offset and push against each other, but when you're talking about piston movement to take up the distance from them being pushed back into the caliper by the wobbly rotor, you have to account for ALL of the pistons.
anyway, despite him trying to tell me that I had 'other problems causing my soft pedal" a new rotor with nearly zero runnout fixed my issue.
**Photobucket sucks**
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Re: Brake bias and caliper BORE size.
[Re: DynoDave]
#1233111
05/17/12 08:37 PM
05/17/12 08:37 PM
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Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog
OP
Striving for excellence
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OP
Striving for excellence
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
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Quote:
This stuff leaves me in a fog.
I wish some of feets' math could be put into a spreadsheet with formulas...put in the value, get the ratio/value out. But I guess it's not that simple.
I thought that I was pretty decent at math. I should clarify... I am pretty decent at ARITHMETIC. The stuff Feets put up is over my head!
I finished the RETURN to power brakes. The car has brake DIVE once again! WOW! All the cussing and frustration.... GONE.
I had another couple of posts in the standard Q&A forum. In one of them, a helpful member listed a link to a vacuum can from Summit racing equipment. It was suggested to me a while back. I should have listened.
Its sad that I didn't figure it out. I looked at the distribution block that I had with the manual setup. I couldn't find anything wrong with it. All this speculation about pedal ratios and caliper force is good diagnostic efforts, but at this point, the problem remains a mystery!
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Re: Brake bias and caliper BORE size.
[Re: DynoDave]
#1233112
05/17/12 11:04 PM
05/17/12 11:04 PM
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Joined: Jan 2003
Posts: 28,067
Irving, TX
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Senior Management
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Irving, TX
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Quote:
This is a good read. I'm sorry it's at Frankenduster's expense, but I'm learning quite a bit. And some o fit, honestly, leaves me in a fog.
I wish some of feets' math could be put into a spreadsheet with formulas...put in the value, get the ratio/value out. But I guess it's not that simple.
It's really simple math. I've pretty good with numbers but when they started putting letters in there I got lost.
The most difficult thing to do is find the area of a circle. It's the radius of the circle multiplied by the radius of the circle then multiplied by 3.14.
If the circle is 3 inches across, the radius is 1.5 inches.
1.5 inches times 1.5 inches times 3.14
2.25 inches times 3.14
7.065 square inches.
Other than that, you're simply playing with numbers.
I really thought about putting them into a spreadsheet just to play with later.
To be perfectly honest, getting too hard core into the numbers can leave you chasing a perfection that you will never find.
As for Frankenberry, I'm glad he got the brakes worked out. 
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Brake bias and caliper BORE size.
[Re: feets]
#1233113
05/18/12 08:48 AM
05/18/12 08:48 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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Quote:
To be perfectly honest, getting too hard core into the numbers can leave you chasing a perfection that you will never find.
Or, in my case, you could run all the numbers, calculate that you need a 7/8" bore master cylinder for that perfect pedal effort on a manual setup, only to have the "expert" at the brake store tell you that you're wrong, and that every manual disc combo really needs a minimum of a 1" bore for fluid volume.
I had a pedal that was too stiff, and I never could lock up the fronts, although I was able to make it stop very hard, so I wasn't too concerned about it.
just annoyed that I allowed myself to be talked out of what I wanted because the guy posed himself as an expert who deals with this all the time
**Photobucket sucks**
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Re: Brake bias and caliper BORE size.
[Re: Kern Dog]
#1233115
05/18/12 06:54 PM
05/18/12 06:54 PM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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You realize that with the power setup you lessen leverage and increase stroke for a given amount of pedal movement.
Your fluid volume was too little with the manual setup, ergo my recommendation to upsize the MC. You get more volume one of two ways, longer stroke, or larger bore.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: Brake bias and caliper BORE size.
[Re: 70Cuda383]
#1233116
05/18/12 07:08 PM
05/18/12 07:08 PM
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Joined: Jan 2003
Posts: 28,067
Irving, TX
feets
Senior Management
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Posts: 28,067
Irving, TX
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Quote:
Quote:
To be perfectly honest, getting too hard core into the numbers can leave you chasing a perfection that you will never find.
Or, in my case, you could run all the numbers, calculate that you need a 7/8" bore master cylinder for that perfect pedal effort on a manual setup, only to have the "expert" at the brake store tell you that you're wrong, and that every manual disc combo really needs a minimum of a 1" bore for fluid volume.
I had a pedal that was too stiff, and I never could lock up the fronts, although I was able to make it stop very hard, so I wasn't too concerned about it.
just annoyed that I allowed myself to be talked out of what I wanted because the guy posed himself as an expert who deals with this all the time
It's kinda funny. As your master cylinder size goes up your pedal effort goes up but the brake pressure goes down.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Brake bias and caliper BORE size.
[Re: feets]
#1233117
05/18/12 07:11 PM
05/18/12 07:11 PM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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Quote:
Quote:
Quote:
To be perfectly honest, getting too hard core into the numbers can leave you chasing a perfection that you will never find.
Or, in my case, you could run all the numbers, calculate that you need a 7/8" bore master cylinder for that perfect pedal effort on a manual setup, only to have the "expert" at the brake store tell you that you're wrong, and that every manual disc combo really needs a minimum of a 1" bore for fluid volume.
I had a pedal that was too stiff, and I never could lock up the fronts, although I was able to make it stop very hard, so I wasn't too concerned about it.
just annoyed that I allowed myself to be talked out of what I wanted because the guy posed himself as an expert who deals with this all the time
It's kinda funny. As your master cylinder size goes up your pedal effort goes up but the brake pressure goes down.
Yup! which is why I was so hesitant after doing my own calculations and decided a 7/8" was what I needed, but started to doubt myself when the "expert" told me I needed a 1" bore.
then once I started driving it, I was annoyed that my pedal effort was harder than I wanted, but not annoyed to the point of wanting to change it
**Photobucket sucks**
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Re: Brake bias & caliper BORE size. Problem found?
[Re: Kern Dog]
#1233123
05/19/12 02:55 AM
05/19/12 02:55 AM
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Joined: Jan 2003
Posts: 28,067
Irving, TX
feets
Senior Management
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Posts: 28,067
Irving, TX
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Many master cylinders use larger fittings on one line. However, the lines themselves are the same size. It keeps people from installing the lines incorrectly.
If the adapter you used did not reduce the fluid passage below the size of the line I don't see where it would have been a problem.
We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon
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Re: Brake bias & caliper BORE size. Problem found?
[Re: ahy]
#1233126
01/26/14 05:56 PM
01/26/14 05:56 PM
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Joined: Feb 2010
Posts: 18,493
Granite Bay CA
Kern Dog
OP
Striving for excellence
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OP
Striving for excellence
Joined: Feb 2010
Posts: 18,493
Granite Bay CA
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Quote:
Also vacuum. Sounds like you have a bigger cam and lower vacuum. PB work best with 18+ vacuum. Anything over 10 or 12 is usually enough for putting around but max assist needs more vacuum. One test would be to get up to speed and downshift so the engine is spinning>2000 RPM with throttle closed. At that point it should be making good vacuum. Are the brakes noticeably better?
At speed, the brakes work fantastic. While rolling along at parking lot speeds, they are not good. I'm sure is related to engine vacuum. It is exactly because of this that I am still curious as to how I could make a manual brake combination work.
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