[31chevy]

Any one know how i can find out how big my rear caliper pistons are on the rear end i want to put under my 32

The rear is disc from a 1998 sonoma

[joe_padavano]

Originally Posted by 31chevy

Any one know how i can find out how big my rear caliper pistons are on the rear end i want to put under my 32

The rear is disc from a 1998 sonoma

Um, use a ruler? Not to be a **********, but the size of the caliper pistons is simply the piston diameter.

[31chevy]

Sorry i meant to ask how do i determine the piston area size needed for my aplication

[powerrodsmike]

You do like most of us, and could make a reasonable guess by looking at a car with similar weight, weight distribution and equipped with brakes that perform at the same speeds you expect to be going, on the same size tires you expect to use,...and get a set of those, or you could work backwards , like the brake engineers do....

Start here.http://www.stoptech.com/tech_info/te...e_papers.shtml

then this:

http://www.stoptech.com/tech_info/Th...%20Systems.pdf

Then read this:

http://www.stoptech.com/tech_info/fo...g_dynamics.pdf

Here is a link to a very good article on Pirate4X4, it has LOTs of good stuff, and is, by far the best online brake design article I've seen yet.
http://www.pirate4x4.com/tech/billavista/Brakes/

Thank Triaged for that one.

Somewhere Triaged had shown me a link to a good online calculator, in an excell spreadsheet format, to do the math once you plug in all of your values, but that was 2 computers ago and I can't find it now...

Ford explorer disc brakes work good, the GM calipers kits for rears that most sell are a PITA.

You don't need alot of rear brake on a 32.

I just noticed on your first post where you said you had disc brakes from a 98 Sonoma, check to see if these are low drag calipers, they cause alot of problems if you don't know about them.
Later, mikey

[Triaged]

I posted one here before that was made for dual master cylinders with a balance bar (like a Wilwood pedal setup).
http://www.hotrodders.com/forum/atta...achmentid=9848
this is where I got it from
http://sceep.boogerwelds.com/sob/jeep_brakes.xls

This one can be found about 2/3 of the way down in the link Mike posted and it is done for a conventional tandem master cylinder. Read the link for the explanation of how it works.
http://www.pirate4x4.com/tech/billav...BillaVista.xls
http://www.pirate4x4.com/tech/billavista/Brakes/

The easy answer is to make sure the piston area and rotor size is the same or a bit smaller on the rear than the front and to put in an adjustable prop. valve.

[powerrodsmike]

Thanks Triaged, I knew that billavista page had a calculator on it somewhere, you sent it to me before but last night I couldn't find it anywhere....

I still owe you a copy of that Ferodo brake engineering handbook from the old days....
( scanned a few pages in and then my scanner crapped out...but I haven't forgotten)

Later, mikey

[31chevy]

Originally Posted by Triaged

I posted one here before that was made for dual master cylinders with a balance bar (like a Wilwood pedal setup).
http://www.hotrodders.com/forum/atta...achmentid=9848
this is where I got it from
http://sceep.boogerwelds.com/sob/jeep_brakes.xls

This one can be found about 2/3 of the way down in the link Mike posted and it is done for a conventional tandem master cylinder. Read the link for the explanation of how it works.
http://www.pirate4x4.com/tech/billav...BillaVista.xls
http://www.pirate4x4.com/tech/billavista/Brakes/

The easy answer is to make sure the piston area and rotor size is the same or a bit smaller on the rear than the front and to put in an adjustable prop. valve.

How much smaller is acceptable for the rear caliper ..

Alot of calculations am going to guessamate the cg and weight of the car and ... make some calculations.

i figure 700 psi will be made from the ratio I plan to use and the mastercylinder 1 inch bore.

now i just need to find out if thats aprropriate for stoping the car and if the calipers can handle that

[Triaged]

I think I'll stick "a bit smaller". Either that or go through all the calculations. An adjustable prop. valve is inexpensive and able to make up for having too big of rear brakes but can't do anything about too small.

[31chevy]

Here my calcs , did i do it right.

(75lbsX6)/ .7854 = 573 max psi out MC (75 lb leg force, 6 pedal ratio, 1inch diam MC)

I know this is the psi in the rear line and front line but does only one front caliper see 573 psi or is it split amongst the two front calipers so that each sees half of 573

Proceeding with calculations

I over assume that my car weighs 2500lb with a center of gravity (found by balancing on jack and 4x4) acting 50" from the front tire. 112" wheel base

Statics problem

Sum of the Forces=0 = 2500 - ForceA - ForceB = 0

Sum Moments about point A (the front axle)= (2500)x 50 - ForceB x (112)

ForceB=1116
ForceA=1384

----------------------


TorqBrequired(for both rear brakes)= 1116X1X15 =16740

15inch radius tire , friction 1, 1116 vert force

ClampForce= 573x ( 5.939x2x2) = 13612.18

max psi x (effective caliper area) . effective caliper area is for a 2.75" diam pist and this effective area = 5.939x 2 x 2 .. theres two calipers and there floating ones thus 2 x 2

Torq brake developed= 13612.18x .3x6= 24502

Clampforcexdiskfrictionxpad arc

is it right


I did calcs for a 2.75" diam piston which is the same size thats i do have for the front . calcs for a 2 and 1/8 pistons put me shy of the needed about
but i did over estimate the total car weight.


So if i did this all right I would purcase metric gm calipers and buy or fabricat this mounts and weld or bolt them to the rear while using the original 3/4" this rotors that are 12 inch in Diam. why because they are the hat style ebrake type.

[Triaged]

See answers in red.

Originally Posted by 31chevy

Here my calcs , did i do it right.

(75lbsX6)/ .7854 = 573 max psi out MC (75 lb leg force, 6 pedal ratio, 1inch diam MC) Yes

I know this is the psi in the rear line and front line but does only one front caliper see 573 psi or is it split amongst the two front calipers so that each sees half of 573 Both front wheels will get 573psi because of Pascal's law that "a change in the pressure of an enclosed incompressible fluid is conveyed undiminished to every part of the fluid and to the surfaces of its container."

Proceeding with calculations

I over assume that my car weighs 2500lb with a center of gravity (found by balancing on jack and 4x4) acting 50" from the front tire. 112" wheel base Ah...the fun way to find the CG

Statics problem

Sum of the Forces=0 = 2500 - ForceA - ForceB = 0

Sum Moments about point A (the front axle)= (2500)x 50 - ForceB x (112)

ForceB=1116
ForceA=1384That is the static load on the tires. You will need to find the weight transfer from the back wheels to the front during braking. In order to do that you need to know the vertical location of the CG. Many people guess'timate it as the height of the top bell housing bolt from the ground.

----------------------


TorqBrequired(for both rear brakes)= 1116X1X15 =16740

15inch radius tire , friction 1, 1116 vert force Friction=1 is for warmed up sticky tires. Friction=0.8 would be better for normal street tires on dry pavement

ClampForce= 573x ( 5.939x2x2) = 13612.18

max psi x (effective caliper area) . effective caliper area is for a 2.75" diam pist and this effective area = 5.939x 2 x 2 .. theres two calipers and there floating ones thus 2 x 2 Clamp force doesn't need the 2nd "x2". However because there are 2 pads I would put it below. Doesn't change your answer

Torq brake developed= 13612.18x .3x6= 24502

Clampforcexdiskfrictionxpad arc


is it right Pad arc should be from the spindle axis to the center of the pad, not half of the rotor diameter (I'm just guessing you are using 12" rotors up front). See what BillaVista has to say about DOT edge codes to find the coefficient of friction of your pads. 0.3 looks a bit low to me if you are using performance pads. My Hawk HPS pads are FF so 0.35-0.45 hot or cold if I recall correctly. http://www.pirate4x4.com/tech/billavista/Brakes/#Pads


I did calcs for a 2.75" diam piston which is the same size thats i do have for the front . calcs for a 2 and 1/8 pistons put me shy of the needed about
but i did over estimate the total car weight. When you include the weight transfer chances are those metric calipers would be a bit big and need a prop. valve (exactly what you want).



So if i did this all right I would purcase metric gm calipers and buy or fabricat this mounts and weld or bolt them to the rear while using the original 3/4" this rotors that are 12 inch in Diam. why because they are the hat style ebrake type.

So you have full size GM brakes in the front with 12" rotors?

[31chevy]

Thanks... I plan on welding caliper brakets on the rear axle or making bolt on one to fit big gm metric calipers. Is it safe to use the original type rotors they are 3/4 inch thick oppesed to the inch thick one in the front. Using there type rotors to keep the stock reares e brak system.

speedway has brackets but they look thin

[Triaged]

Didn't GM make "metric" calipers that were for a 0.84"ish rotor? I don't know how much piston stick-out is ok. You want to be sure the piston won't pop out when the rotors are at discard thickness and the pads worn down to steel. You might also want to read up on the low-drag calipers. There have been a few threads recently about not being able to get the older non-low drag calipers. You might need to run a residual pressure valve and/or a manual brake S10 master cylinder if you can only find low-drag calipers.

[powerrodsmike]

Great stuff
I wished I could figure out how to do the math part..Oh well.
IIRC, some of the circle track supply places like coleman racing and speedway motors (in the race catalog) sell pad spacers to make a metric caliper run on the thinner rotor....

Later, mikey

[31chevy]

How do you guys feel about piston spacers or brack pad shims. Im looking a running a caliper meant for 1 " thich rotor on a 3/4" thick rotor

[powerrodsmike]

A friend of mine has 1/8" spacers tack welded to the back of the pads on the front of his 46 Ford PU, his MII kit from Fatman came like that, he's been running them for years with no problems.

Later, mikey