master cylinder bore question
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master cylinder bore question
I am in the process of collecting all the parts I need to build the entire front of my project 88 bird. I know bore sizes differed from some years, what is the best master cylinder to get?? I assume the bigger the bore the better??
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No.
The bore size is like a lever.
Imagine if you had the MC bore and the caliper bore the same size, let's say 1 sq in of area, and you had to push it 1" to move the slave cylinder the correct amount to do its thing; then, if you put let's say a hundred pounds on the MC, you'd get a 100 psi in the system, and the slave would exert the same hundred pounds on its load, and would move 1".
Now imagine that you made the MC bore 2" in area. And, imagine that you put the same 100 lbs of force on it. Now, instead of what it did before, it would produce only 50 psi in the system (100 lbs divided by 2 sq in); and would only move half as far to displace the same amount of fluid. That is, to get the same results of 100 psi in the slave moving it 1", you'd have to put 200 lbs of force on the MC, and only move it half an inch. If you did that, you'd end up with a pedal that felt very hard and high, that you'd about have to get up out of your seat and stand on, to get the desired braking action.
Now imagine that you reduce the size of the MC, to 1/2" area. Now, to get that same action at the slave, you'd use 50 lbs of force, but it would have to move 2". Now you'd have a pedal that felt soft and low, but would nose the car over with just a toe being applied to it.
The sizes of all the hydraulic parts are designed as a SYSTEM. That is, they calculated how much clamping force was needed at the brake pads, how hard the average person could push the pedal, how far the pedal could travel, etc.; and selected bore sizes, the location of the stud on the pedal, etc. accordingly.
There is little or nothing to be gained by just arbitrarily changing ONE part of the SYSTEM.
On the other hand, if you were to put different calipers in, with different sized pistons, then you would HAVE TO change the MC diameter; or its throw; or something, to make up for the altered hydraulic characteristics of the slave.
The best MC to get, asuming you have the stock calipers and slave cylinders, is a stock replacement one. Obviously a high-quality, well-made one, if possible; but a stock replacement just the same.
The main difference in bore size from one year to another, involved the cast-iron (82-88) Saginaw calipers. The drum brakes and the PBR calipers have similar hydraulic requirements and so use the same MCs.
Just get the right cyl for the brake system you have.
The bore size is like a lever.
Imagine if you had the MC bore and the caliper bore the same size, let's say 1 sq in of area, and you had to push it 1" to move the slave cylinder the correct amount to do its thing; then, if you put let's say a hundred pounds on the MC, you'd get a 100 psi in the system, and the slave would exert the same hundred pounds on its load, and would move 1".
Now imagine that you made the MC bore 2" in area. And, imagine that you put the same 100 lbs of force on it. Now, instead of what it did before, it would produce only 50 psi in the system (100 lbs divided by 2 sq in); and would only move half as far to displace the same amount of fluid. That is, to get the same results of 100 psi in the slave moving it 1", you'd have to put 200 lbs of force on the MC, and only move it half an inch. If you did that, you'd end up with a pedal that felt very hard and high, that you'd about have to get up out of your seat and stand on, to get the desired braking action.
Now imagine that you reduce the size of the MC, to 1/2" area. Now, to get that same action at the slave, you'd use 50 lbs of force, but it would have to move 2". Now you'd have a pedal that felt soft and low, but would nose the car over with just a toe being applied to it.
The sizes of all the hydraulic parts are designed as a SYSTEM. That is, they calculated how much clamping force was needed at the brake pads, how hard the average person could push the pedal, how far the pedal could travel, etc.; and selected bore sizes, the location of the stud on the pedal, etc. accordingly.
There is little or nothing to be gained by just arbitrarily changing ONE part of the SYSTEM.
On the other hand, if you were to put different calipers in, with different sized pistons, then you would HAVE TO change the MC diameter; or its throw; or something, to make up for the altered hydraulic characteristics of the slave.
The best MC to get, asuming you have the stock calipers and slave cylinders, is a stock replacement one. Obviously a high-quality, well-made one, if possible; but a stock replacement just the same.
The main difference in bore size from one year to another, involved the cast-iron (82-88) Saginaw calipers. The drum brakes and the PBR calipers have similar hydraulic requirements and so use the same MCs.
Just get the right cyl for the brake system you have.
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