Here is the set up on my 1200:
280ZX front calipers, 240Z master Cylinder, 510 rear shoes w/ 13/16th wheel cylinders and 240Z alloy drums.
I want more rear brake in the car; I end up locking the fronts well before the rears
I have 7/8ths wheel cylinders on the shelf but my thought is they likely won't make that much of a difference. The only other thing I can think to do is a more aggressive rear shoes.
Thoughts? (yes I know the real solution is to fab up a brake balance bar with duel masters).
If its a 1" piston a 1 - 1/16" (1.0625") diameter piston has 13% more area.
Just square the diameters of each and divide the smaller one into the bigger one to get the percent change.
Yup. You'll get roughly 16% more braking force for a given pedal pressure.
In reply to APEowner :
That's a lot more than I thought it would be for a 7.7% larger cylinder.
Guess I'll be fitting them.
It's really come to the fore after a track day this past weekend. There is a 60 degree right sweeper leading into a tight 90 right. I can tell I'm repeatedly locking the inside front wheel................even before this happened. Note those tires are on there 21st heat cycle.
APEowner said:Yup. You'll get roughly 16% more braking force for a given pedal force.
fixed
In reply to AngryCorvair (Forum Supporter) :
So how do I calculate this I.E how did we arrive at 16%??
Like jharry3 said:
Just square the diameters of each and divide the smaller (OLD) one into the bigger (NEW) one to get the percent change.
so NEW wheel cylinders have about 16% more piston area, which in theory should result in 16% more brake output from the rears.
lunch is not free. your payment is that the brake pedal travel due to rear brakes will increase by 16%.
I use OLD and NEW instead of smaller and bigger because the math works in both directions. if you had too much rear brake and wanted to reduce output, your NEW would be smaller than your OLD and your percentage would be negative, ie a decrease in area to give a decrease in output.
In reply to AngryCorvair (Forum Supporter) :
Would the pedal travel increase by 16% or less since the fronts aren't changing? Meaning wouldn't the fronts have to go up by 16% for the travel to go up exactly 16%?
Stampie said:In reply to AngryCorvair (Forum Supporter) :
Would the pedal travel increase by 16% or less since the fronts aren't changing? Meaning wouldn't the fronts have to go up by 16% for the travel to go up exactly 16%?
perhaps my choice of wording wasn't great, but what i meant is that the pedal travel will increase, due to the rear wheel cylinders being 16% larger. ie "the amount of pedal travel that is due to the rear brakes will increase by 16%."
i said:
lunch is not free. your payment is that the brake pedal travel due to rear brakes will increase by 16%.
In reply to AngryCorvair (Forum Supporter) :
It's ok. I still love ya.
AngryCorvair (Forum Supporter) said:APEowner said:Yup. You'll get roughly 16% more braking force for a given pedal force.
fixed
You sir, are correct.
In reply to AngryCorvair (Forum Supporter) :
That's perfect; it should occurred to me that "area" was the operative word.
As for pedal travel that's not really an issue; I'm using a 240Z master and so the pedal travel would be about the same as the stock 240Z as all the parts will now be Z car.
AngryCorvair (Forum Supporter) said:Like jharry3 said:
Just square the diameters of each and divide the smaller (OLD) one into the bigger (NEW) one to get the percent change.
- OLD: (13/16) * (13/16) = 0.6601 sq in
- NEW: (7/8) * (7/8) = 0.7656 sq in
- NEW divided by OLD = 0.7656/0.6601 = 1.1599
so NEW wheel cylinders have about 16% more piston area, which in theory should result in 16% more brake output from the rears.
lunch is not free. your payment is that the brake pedal travel due to rear brakes will increase by 16%.
I use OLD and NEW instead of smaller and bigger because the math works in both directions. if you had too much rear brake and wanted to reduce output, your NEW would be smaller than your OLD and your percentage would be negative, ie a decrease in area to give a decrease in output.
For those who are trying to figure out what Angry is doing, he's eliminated pi from the equation because it's a constant and used the diameter because the math works out the same as the radius. It's a shortcut that works because you're looking at ratios. The area of the old cylinders aren't 0.6601 square inches, they're 0.51848. But that's okay, because the new one is also inaccurate in the same way so the ratio works out :)
It's really "pi R squared". That requires more math to get to the same result, but it's more complete so it might be easier to remember. At least, it is for my brain - it's easier to derive the ratio from two areas than to remember the shortcuts because I don't do it every day.
AngryCorvair (Forum Supporter) said:perhaps my choice of wording wasn't great, but what i meant is that the pedal travel will increase, due to the rear wheel cylinders being 16% larger. ie "the amount of pedal travel that is due to the rear brakes will increase by 16%"
Why wouldn't the pedal travel increase also result in more front brake pressure?
jfryjfry said:AngryCorvair (Forum Supporter) said:perhaps my choice of wording wasn't great, but what i meant is that the pedal travel will increase, due to the rear wheel cylinders being 16% larger. ie "the amount of pedal travel that is due to the rear brakes will increase by 16%"
Why wouldn't the pedal travel increase also result in more front brake pressure?
No, the pedal travel is to maintain the same pressure while the rear brakes need more volume.
porschenut said:jfryjfry said:AngryCorvair (Forum Supporter) said:perhaps my choice of wording wasn't great, but what i meant is that the pedal travel will increase, due to the rear wheel cylinders being 16% larger. ie "the amount of pedal travel that is due to the rear brakes will increase by 16%"
Why wouldn't the pedal travel increase also result in more front brake pressure?
No, the pedal travel is to maintain the same pressure while the rear brakes need more volume.
kinda this. the two pistons in the master cylinder move independently, so (as long as they are the same diameter) the resultant pressure in each circuit is the same, independent of the volume of fluid required by the downstream brake components.
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