better brakeing....master cylinders

malibu795

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Apr 17, 2005
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found my 79 oem MC is pretty darn small... and results in longer pedal travel for effective braking IMO
24mm/0.944" bore (power)(m1738)
7/8"0.875" bore for manual brakes.(m1737)
84 MC
diesel 1 1/16/1.061" (M1902)
gass 36mm (1.41") M1926(az)
all of them run 1/2x20 and 9/16x18 line boses
 

Doober

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Jun 2, 2003
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We kind of went over this a few days back with bu min v8.
http://maliburacing.com/forum/viewtopic.php?f=2&t=101172

What follows isn't necessarily directly at you, though if it helps you understand things more, all the better 8)

The larger master would indeed cause the calipers to clamp sooner/faster, but they won't apply as much pressure with the same amount of pedal travel, so braking wouldn't be as effective. I believe you will have the same issues he does if you swap them and don't use the proper booster... I'm not sure why they have 2 different masters because all the calipers I saw had the same sized bores, which doesn't really make sense, unless the rod is closer to the pivot on the brake pedal.

Think of a pushpin.
images


Now try pushing the blue end of that pin through your finger. You can't without a whooooooole lot of pressure, right? That's basically the same thing that's happening when you go to a larger master cylinder bore. Now flip that pin around and do the same thing... the pin goes right in, doesn't it? That's because the pressure is focused on one small area as opposed to a larger area with the blue end. That's part of hydraulics in a nutshell... the other part is the pedal travel thing, but that doesn't necessarily apply to pressure, it's just how much pedal movement is required for the same amount of caliper movement, not as much would be required with the larger bore as you mentioned, but a lot more pressure would be required.

If you want serious braking you would be better off upgrading to larger rotors as well (along with going to discs on rear imo, though there are differing opinions on that I think), with calipers to better match your new master cylinder bore.
 

malibu795

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not what im after ;)
he has/had a booster problem.

im looking more to mechanics of it.. speed of the brakes applieing and hyd forcce one can create.
if we remove hyd/vac booster(which adds addition applied force to MC piston) and say an avg man can apply 600lb of force on the MC piston and an avg stroke of the piston is 0.75" and to simplifiy things for debating purpose its a single piston MC so volume is stroke (.75")x bore= in3
so the formula for HYD force is piston area x force applied to piston. IE 10LB applied to 1sqin =10psi.
knowing that with the mechanical force and oem brake pedal and avg person can apply 600lb of force to the MC pushrod. i will keep that as a constant. and the max stroke distance of .75" constant as well though it would on refer to speed at which the brakes can be applied in realtion to the brake pedal moving.

i am leaving out HYD/VAC booster since both very drasticly based on engine vaccum/power steering pump pressure setting. all they do is supply addition regulated force to what ever your foot is appling to the MC thus allowing the operator to have to push less harder on the pedal to reach suffiecent pressure to slow the vehicle. it is much simpler to discuse a basic manual system and would like your opinion on HYD pressure one can create at the MC.

a 7/8" bore has 2.74sqin 600lb will generate 1644psi of HYD force
a 24mm bore has 2.96sqin 600lb will generate 1776psi of hyd force.
a 1 1/16 bore has 3.33sqin 600lb will generate 2000psi of hyd force.
a 36mm bore has 4.45sqin 600lb will generate 2600psi of hyd force.

like your thumb tac example i am only talking about the part you press your thumb on. i know fo fact that the rear wheel cylinders are .75" bores which is 2.35sqin this would be pin part of the tac. with the smallest bore info i posted this wheel cylinder wouldl generate 3863lb of mechanical force against the rear brake shoes. this results in the MC having to travel 85% of the distance the wheel cylinder has to travel before making contact with the drum. this transelate into long brake pedal travel.

pedal feel and travel. a smaller MC piston will be easier to push then a larger piston the downside to smaller driving piston is it have to travel farther to net same travel results from the wheel cylinder then a larger driving piston.
the weird thing is the smaller MC the operator will actually be pushing harder on the smaller driving psiton to get sufficent force to stoping force at the brakes then the larger MC.

heres an example keeping the same 3/4" dia wheel cylinder lets hypotheticly say 3800lb of mech force locks up the rear tires and 3500lb is considered a hard stop. from 2 pharagraph up we already know if an operator has a 7/8 bore MC he is goign to need appliy 541lb of force on the MC via the brake pedal with the MC traveling 85% of hte distance the wheel cylinder has to travel.
if the operator has a 1 1/16 bore the operator will only have to apply 447lb to the MC via brake pedal. this MC only has to travel 70% of the distance the wheel cylinder has to travel.

with that said it would be evident to say the bigger MC allows for quicker application of the brakes and with less pressure applied via the operator to reach the hard braking threshold.

with those examples its clear to say a bigger MC will increase braking capability if everything else remains constant in the HYD brake system...

now the booster reduce the amount of force the operator has to put to the MC via the brake pedal.
a 7" diapharm with 15inhg applied to it will generate max of 1271psi of regualted force on the MC thus drasticly reducing the amount force the operator has to applie via the brake pedal.
a HYD boost is much more the power steerin pump is set between 900-1000psi at the pressure releif valve operating is about 850psi with a 1 1/4 bore in the booster with a max applied pressure of 3336psi of regulated force that can be applied to the MC on top of what the operator applies.
 

malibu795

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Update on my old thread.. Still running the 1.41" bore MC..
Finally dawned on my why rear brakes hit faster then front... It's simple fluid dynamics.. Increase pump volume.. You need to increase line size to handle said volume increase especially going from a 24mm to 36mm bore MC.
Rear line been 1/4" for long time.. Front was 3/16 from MC to proportions valve... Swapped in a 1/4" line

Problem fixed.
Definitely help when I put big C5 caliper on and to handle extra volume they take
 

malibudave1978

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Jun 8, 2004
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Adam,

Thanks for your service.

Adding a 1/4" brake line will not change the performance of your brakes. If you didn't change anything else but the line, I am guessing you had air in front brake lines or some other issue that was corrected when you changed the line.

1. Brake line size does not matter. The amount of fluid in the line is always constant, so adding a 1" diameter line will make no difference. The amount of volume supplied to the calipers is dictated by the master cylinder only. A brake caliper or wheel cylinder will only need a certain volume of fluid to fill its bore and that volume comes from the master cylinder only.

2. Your master cylinder is a step bore master cylinder. It has a 1.41" primary bore, and a 24mm secondary bore. A step bore master cylinder was developed to be used with LOW drag calipers, which require more fluid volume to operate correctly (the larger 1.41" bore supplies the needed volume, the 24mm bore supplies the needed pressure). It has a built in bypass valve that transitions from the 1.41" bore to the 24mm bore at 100lb of line pressure. Technically, you still have a 24mm bore to supply the needed pressure in the system, but you will get less pedal travel because of the larger 1.41" diameter primary bore supplying more volume. Its the best of both worlds even with normal, NON low drag calipers, but these master cylinders are hard to bleed and have additional parts (100lb bypass valve) that can fail and cause braking grimlins. Aluminum versions of the master cylinder will be rebuilt units and the new ones will be cast iron. The cast iron ones are pretty heavy because the housing on both are so large.

3. Your C5 calipers have a 2 pistons that are 40.5mm or 1.59" in diameter. Though the caliper is physically larger, the total piston area for the C5 caliper is 3.99 sqin. The stock malibu front caliper has a one piston with a diameter of 2.38" (or 2.5" depending on where you measure). The stock malibu caliper has a piston area of 4.45 sqin ( or 4.91sqin depending on where you measure). The stock malibu caliper will require more volume of fluid that a stock C5 corvette caliper. Techically, with all things being equal, the stock malibu caliper generates more clamping force because of the larger piston area, but all things are not equal between a stock malibu caliper and a C5 caliper. The Corvette caliper is more likely a stiffer caliper and will have less deflection. The Corvette caliper is also clamping down of a significantly larger rotor which helps braking performance.

Most performance calipers are about the same piston area or smaller than a stock malibu caliper, regardless of the number of pistons. More caliper pistons do not always need more volume fluid or do they generate more clamping force.
 

malibu795

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Dave
Thank you

If you increase flow above what a said line can handle then it becomes a restriction/orfice. Simple fluid dynamics.

I have ran gallons of brake fluid through the front system. Via normal/pressurized/and vaccum methods not necessarily in that order. No air bubbles

Given piston size of stated C5 2 pistons with a size of 1.59" dia is 9.98sqin combined of piston surface with each piston has 4.99sqin
2.38" piston has 7.47sqin
2.5" piston had 7.85 sqin
Wilwood 140-12629-R drop in 6 piston c5 calipers have 6 1.25" bore pistons for combined total of 23.55sqin of piston surface. That's 235% more clamping surface then stock C5 and more then 300% bigger then either stock calipers...

In short more volume is need to move the stock C5 pistons same distance as a stock Gbody, or anything bigger for that matter..

Either one of two things happens.. Increase pedal travel to achieve volume needed and slow response time of brakes.. or increase pump volume(bigger MC) which decrease or keeps pedel travel roughly the same to move pistons the same distance..and can turn brake lines into restrictions.. Because the cant handle volume in time frame required, which would cause hard pedal application and long release times, obviously fluid has to go right back the line it just went through.. At less pressure.

Brakes are a basic simple fixed volume hydraulic system.
Change caliper, number and size, change MC size, and line diameter all will affect F/R bias, response in apply/release of brakes and feel of brake pedal when applying brakes
 

malibudave1978

Amateur Racer
Jun 8, 2004
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Adam,

Please let me know if I am incorrect.

Area of a circle (caliper piston diameter) is calculated:
radius of a circle X radius of a circle X Pi
or
r X r X Pi

radius of a circle is 1/2 the diameter of a circle
Pi = 3.14

Half of 1.59 = .795 = radius

Area of a C5 caliper piston's diameter is:
.795 x .795 x 3.14 = 1.98456

You have two pistons in a C5 caliper:
1.98456 x 1.98456 = 3.96912 sqin

area of a metric malibu front caliper with a 2.38 diameter piston is:
1.19 x 1.19 x 3.14 = 4.44655 sqin.

If my math is incorrect, please let me know.

"The volume of fluid moved through a brake system is determined by the MC piston bore and the caliper piston bores. Assuming that the fluid is incompressible, then what goes in, must come out. If we ignore line size and push a volume of 10cc of brake fluid in one end of a brake line with the MC, 10cc will come out the other end, regardless of diameter, length, or pressure. The brake line could be .06" or 6" in diameter and that would still be true as long as we assume that the tubing doesn't expand." Tobin "Apogee" from Kore3.com. He knows more about brakes than I do.
 

malibu795

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Yes math is correct I screwed up the area..

Flow wise..
moving 10cc through a 0.6" line will be easier and faster then trying to shove 10cc through a 0.06" line
 

LS6 Tommy

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May 15, 2004
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malibu795 said:
Yes math is correct I screwed up the area..

Flow wise..
moving 10cc through a 0.6" line will be easier and faster then trying to shove 10cc through a 0.06" line


Only if the end of the line is open. It doesn't work the same with hydraulics. In a closed vessel (like brake system) pressure is the same everywhere. No pressure drop, no volume change... Only master cylinder piston size & stroke dictate fluid volume. Different line sizes only affect total system fluid capacity.

Tommy
 

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