My Big Brakes - 14"x1.25" with viper calipers on all 4

Posted By: Uhcoog1

My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/13/13 11:41 PM

JCC asked me about my floater axle, and we got to talking brakes, and he suggested I post about my brakes.

Front:
Dr Diff kit - Gen III viper front calipers on SRT8 14.1x1.25" rotors. The rotors weigh about 27 pounds each (!), and the hubs are aluminum. The kit uses 73+ disc brake spindles and a caliper mounting bracket he makes. The brakes fit inside factory GT500 wheels (18x9.5 with 45mm offset). This wheel also fits around the tie rod end, which allows for the 7.2" of backspace. *With this combo, the tire hits the frame before lock on my duster.

Rear:
Schreiner Enterprises 9" floater using 5x4.5" hubs, Coleman 14x1.25" rotors, Gen III viper front calipers, and brackets I made. I went with a floater axle so I could run 4 piston calipers and not worry about pad knockback. The brackets consist of cut down GM Metric caliper brackets bolted to 1.25x1.25x8.5" aluminum stock. The caliper brackets run a full 360* around the axle - made for a much easier job!

Pads:
Cadillac CTS-V factory pads - they are branded "Brembo", and are a Ferodo HP1000 compound (same compound that probably all 'brembo' branded pads use, including the new Camaro, Viper, and high end exotics). The CTS-V pads are .300" taller than the viper pads, otherwise they are the same dimensions. They are the same size pad used on the Viper ACR-X, which uses these exact calipers. The pads fit height-wise on my rotors (just barely). They cost less than Viper brembo pads, though some aftermarket pads cost more in this size (vs viper size). I will probably have to stagger the pad compound to get the bias right, but I'll wait to fix it once I know I have a problem.

Master cylinder: 15/16" from Dr Diff. Manual. Should be about right, but if not, I'll change it out.

Wilwood proportioning valve - I'll probably need all 58% reduction in line pressure to get close to the right bias at threshold braking. With sticky tires, I'll end up with a more aggressive pad in the front.

The car isn't running, but I'll report back once it is, let ya'll know how this thing stops. The goal of the car is to run with a C6 Z06 and porsche GT3 on a road course.

Pics:

Posted By: 70Cuda383

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 12:03 AM

Nice!!

any reason why you went with the same size caliper in the back instead of running the Gen 3 rear viper calipers, which are also a 4-piston design that looks like the fronts, but with smaller pistons.

I put gen 2 front brakes on all 4 corners on my Dakota, with 13" rotors (same bolt pattern as Viper) but I have factory RWAL that keeps me from locking up the rears. --and it works great despite the RWAL being designed for a disc/drum system.

Posted By: Uhcoog1

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 12:41 AM

I bought a set of 4, and they ended up being two sets of fronts. Not a huge difference in volume (4.3 sq/in vs 3.9 sq/in).

Posted By: 72Swinger

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 12:45 AM

Same brakes I have in the front.

Attached picture 7587271-004.JPG

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 05:30 PM

How much room did you have on the spindles?

When I did my 8 piston calipers on the same diameter rotor it was a really tight fit. There was only one place I could mount the calipers and that spot allowed about 1/2" of wiggle room. The lower ball joint, upper control arm, and sway bar prevented stuffing it anywhere else.

I kept my TSM rear lower bracket adding spacers to bring them into position. The biggest difference being that I kept the 8-3/4" rear end.

Posted By: AlexP

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 06:05 PM

Thanks for making me have brake envy.

Posted By: Uhcoog1

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 06:59 PM

Quote:

How much room did you have on the spindles?

When I did my 8 piston calipers on the same diameter rotor it was a really tight fit. There was only one place I could mount the calipers and that spot allowed about 1/2" of wiggle room. The lower ball joint, upper control arm, and sway bar prevented stuffing it anywhere else.

There's a good bit more room between the caliper and the spindle. I'm still amazed you got those 8 piston calipers to fit! Here's a couple pics for you:

Quote:

I kept my TSM rear lower bracket adding spacers to bring them into position. The biggest difference being that I kept the 8-3/4" rear end.

Do you have any pad knock back with the 4 piston in the rears? How much endplay do you have?

Quote:

Thanks for making me have brake envy.

For those of you who don't know, Alex is no stranger to big brakes. His current 6 piston project:

Posted By: Viol8r

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 07:11 PM

We have built similar set-ups on other cars, and unfortunately with e 15/16" M/C and no help behind it, you will drive it the first time and most likely it will not stop! We learned our lesson a while back.... This type of set-up could need hydraboost and some other type of unique boosting system.

Let us know if it works out as-is.

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 07:21 PM

I use a manual 1-1/8" MC from a D150 and it works great. The pedal feels great. It's a bit lighter than the factory manual drums but not as soft as a typical power brake system.

My caliper volume is different than the Viper setup but it still demonstrates the ability to use a common manual MC on a big brake system.

When fitting my calipers, I mounted a rotor, wired it to prevent movement, and wedged a caliper in place using the brake pads and wood shims. Running the suspension through the full range of motion including steering angles put the caliper in it's place. I have about 1/4" of clearance to the upper control arm and about that much between the lower inner edge of the caliper and the ball joint arm.

I got lucky. Fitting those things had not even crossed my mind when I dropped the cash for them.

Posted By: Uhcoog1

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 07:52 PM

Quote:

We have built similar set-ups on other cars, and unfortunately with e 15/16" M/C and no help behind it, you will drive it the first time and most likely it will not stop! We learned our lesson a while back.... This type of set-up could need hydraboost and some other type of unique boosting system.

Let us know if it works out as-is.

Have you had success keeping any of those cars with manual brakes, just with a larger master cylinder?

I don't imagine I'll need a booster, but I haven't ruled out a different size master cylinder. Something I haven't found a way to calculate is what is too small of a master cylinder. The formulas will tell you what is too big (i.e. you'll know when you don't have enough pressure), but nothing really indicates when it gets too small (and you don't have enough pad movement). Any thoughts on this?

Feets - your brake worksheet shows pad movement of .0056 with my application assuming 6:1 pedal ratio and 5" of pedal movement. The formula doesn't make sense to me, so doing it my way, I got .0334" per caliper of clamping movement with the above numbers.
Here are my numbers:
4.3 sq/in area per caliper (one side only, 44mm/40mm - all 4 are this)
0.69 sq/in - master cylinder volume given the above movement (15/16 mc)
= 25:1 total caliper to master cylinder area *This might be a good measurement to compare different brake set-ups for going too small of a master cylinder - might tell us when a M/C is too small*

*What I don't know is how much the pads retract when released, how much pad knockback occurs, and how much fluid compression occurs. That's what really matters in determining when you've gone with too small of a master cylinder, yes?

Feets- what size master do you have? What is the area of your front calipers and rear calipers? You are running manual brakes, yes?

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 08:17 PM

My front calipers have two 28mm and two 32mm pistons per side. The total volume is less than you'd think.
The rears use 28mm and 30mm pistons. Again, fairly low volume.

The manual master has a 1-1/8" bore.

If you're getting more than .010" pad movement then something is wrong. Brake pads normally ride a couple thousandths of an inch off the rotor. Anything more will lead to a squishy pedal.

Posted By: Uhcoog1

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 08:56 PM

Quote:

Are you using square inches?

square inches = area

cubic inches = volume

My front calipers have two 28mm and two 32mm pistons per side. The total volume is less than you'd think.
The rears use 28mm and 30mm pistons. Again, fairly low volume.

The manual master has a 1-1/8" bore.

If you're getting that much pad movement then something is wrong. Brake pads normally ride a couple thousandths of an inch off the rotor. Anything more will lead to a squishy pedal.

I just didn't understand your formula for brake pad movement in the spreadsheet that is here:
http://3gduster.com/brakes.html

Instead, I calculated the volume displaced by the master cylinder:
((.9375/2)^2)*3.1416*.8333 = .5752 ci (MC displacement)

and then calculated the movement of a single piston with that volume with an area of 17.2 (4.3 sq in per caliper * 4 calipers).
.5752 / 17.2168 = .0334" of movement

Note: I then checked the math in excel, calculating the volume of a cylinder for four 44mm cylinders and four 40mm cylinders:
((44/25.4/2)^2)*3.14*.0334 = .0787
((40/25.4/2)^2)*3.14*.0334 = .0651

BTW- your total piston area in the front is ~4.4 sq in.

**I'm not arguing the brake pads actually move this much. All of this is just an exercise in determining when you have too small of a master cylinder.

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 09:26 PM

Quote:

and then calculated the movement of a single piston with that volume with an area of 17.2 (4.3 sq in per caliper * 4 calipers).
.5752 / 17.2168 = .0334" of movement

There's the hitch in your getalong. You should only look at one pair of calipers.
The master cylinder has a single bore but it is divided into two sections. One for the front and one for the rear.
In effect, it's a separate master for the front and another for the rear.

Quote:

Note: I then checked the math in excel, calculating the volume of a cylinder for four 44mm cylinders and four 40mm cylinders:
((44/25.4/2)^2)*3.14*.0334 = .0787
((40/25.4/2)^2)*3.14*.0334 = .0651

There's hitch number two. You do not use both side of a multipiston caliper. You only do one side.

Quote:

BTW- your total piston area in the front is ~4.4 sq in.

The original 2.75" calipers on my Imperial (and several other cars) measure 5.9 sq inches.

To determine if the MC is too small, look at the pressure generated vs the pad movement.
High pressure at low movement = too small.
Low pressure at high movement = too large.

Posted By: Uhcoog1

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 09:45 PM

Thanks for pointing out the MC error!

Quote:

To determine if the MC is too small, look at the pressure generated vs the pad movement.
High pressure at low movement = too small.
Low pressure at high movement = too large.

Any rule of thumb for the above rule?

Posted By: Uhcoog1

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 10:12 PM

I found an interesting point of reference offered by Mark Williams:
http://www.markwilliams.com/braketech.aspx

Rule of thumb from their website:
9.6 sq in = 7/8 MC
14.4 sq in = 1" MC
19.2 sq in = 1 1/8 MC

Posted By: 72Swinger

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 10:26 PM

From what Feets is describing I need a larger master than my 15/16". I need to push pretty damn hard on the pedal to get a hard stop.

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 10:38 PM

Rule of thumb?

Well, who's thumb are you using? My thumb is likely different than yours.

The feel is a personal thing.
As a general rule you want about 1000 psi of pressure at the caliper.
Now to put a wrench in things...

When you have a longer lever arm (read larger diameter rotor) you won't need quite as much pressure. It's like having a longer wrench. You don't need to pull as hard to get the same torque.

That means you can use a bit less pressure with larger diameter rotors. What doesn't change is pad movement.
To get an idea how far your pads move, run the numbers on your stock stuff. Try to work out similar pad movement at a reasonable pedal travel and pressure.

Clear as mud?

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/14/13 10:44 PM

Quote:

From what Feets is describing I need a larger master than my 15/16". I need to push pretty damn hard on the pedal to get a hard stop.

That generally means your MC is too big.
It works a little backwards.

Big MC + small calipers = hard pressure
Small MC + big calipers = low pressure

You have to fiddle with it a bit to get the numbers you want. That was one reason for the spreadsheet. It's easier to play with numbers than it is to swap parts.

Posted By: Winchester 73

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/15/13 06:23 AM

i think the book was "driving to win by jackie stewart?"

research concluded that a driver could mentally modulate leg power better if it dident have movement in the equation so cars were setup with as solid a brake peddle as possible.a driver could "hit" the peddle with a more accurate amount of force without movement in the brain as well.

does this aply to our cars or gocarts on steroids where mechanicle advantage may not be nessesary i have no idea.i have however puty a big bore aluminum mas cyl on a 4 wheel drum 69 dodge truck,the peddle felt like it bent more than it moved

it seemed like i could stop perfectly on a mark with it stopping.it was just an experiment, i changed it back before i sold it.

i wonder how much leg power factors into this,8 months ago i was leg pressing 1000 lbs.i had to stop leg training due to hitting my knee REALLY hard on the asphalt and after that all lifts felt really spooky.i kept waiting for it to go away but it wouldent.about three weeks ago i just said o well and started leg work again.after a couple leg workouts it feels fine but the presses have been kept under 800lbs.leg feels fine so ill be strong again in no time

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/15/13 02:56 PM

Do whatever you want on your car but I'm not going to live with a solid brake pedal.

Pressing 300 lbs on your brake pedal to stop the car at every red light and stop sign would get old VERY quickly. Think about it. How many one leg 300 lb presses can you do? Now, how many times do you hit the brakes on your way to work? No matter how He Man you think you are I bet the brake pedal would still win.
It would also be hard on the seat frame and floor.

Some people forget that we drive these cars for pleasure.

Posted By: Uhcoog1

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/15/13 06:03 PM

I did some playing around with a bathroom scale and the brake pedal in my truck one day. If I recall, 40-50 pound required very little effort, and 70-80 pounds of pressure was fairly easy. Effort was required around 120 pounds, and 150 pound was starting to lift me out of the seat. Kind of told me I'd prefer threshold braking to be below ~120 for road course work. A lower seat to brake pedal angle would have helped.

That being said, F1 drivers use approximately 190-200 pounds of force at threshold braking.

Posted By: AlexP

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/15/13 06:57 PM

I learned that it's hard to go from stock brakes to big brakes...and then back to stock brakes. Once you've had the confidence of a BBK, all stock brakes seem scary.

I had a 355mm Brembo GT1 caliper with a 2 piece rotor on on my GTI. They were amazing. It's the F40/F50/Aston/Viper etc 4 piston caliper.

Now for a 6 piston Cayenne Brembo on a 330mm rotor to fit under 17 inch wheels.

Wade's got me convinced to get AndyF's Viper 4 piston (same caliper as my Brembos) for my 11.75's withn a really good pad.

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/15/13 07:42 PM

I don't have any Cayenne calipers but I've got a 6 pot unit off a Maserati.
Oh yeah, I've got a spare pair of 8 pot AMG calipers for the Imp.

Posted By: Winchester 73

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/16/13 02:40 AM

Quote:

Do whatever you want on your car but I'm not going to live with a solid brake pedal.

Pressing 300 lbs on your brake pedal to stop the car at every red light and stop sign would get old VERY quickly. Think about it. How many one leg 300 lb presses can you do? Now, how many times do you hit the brakes on your way to work? No matter how He Man you think you are I bet the brake pedal would still win.
It would also be hard on the seat frame and floor.

Some people forget that we drive these cars for pleasure.

the numbers are confusing you i think.a leg press is different than pressing a brake peddle.stand on on foot and see ho many times you can lift your body ONE INCH.i am 210 lbs and can do it 20 times fast before it starts to get tiring and thats one rep after another.so if i lived in peru i could drive and not get leg fatige-no body stops that often or repeatedly.in traffic how much of the peddle do you think you need?you wouldent use the whole 300 lbs and on a roadcourse the 300 would likely not thru the whole braking.

f1 drivers use 190lbs?those guys are all the size of jockeys-cept for Dannica patrick -shes got a little meat on her bones.

Posted By: feets

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/16/13 06:52 AM

Once again, you do what you want with your car.

I do not want a solid brake pedal.

Since you like the idea so much, why don't you run the numbers and tell us what kind of pedal arrangement and master cylinder it would take to get a 200 lb (since it doesn't have to be 300 lb) push on the pedal that generates no appreciable movement but still gives you 1000 psi at the calipers and between .003" and .008" of pad movement.

Posted By: Winchester 73

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/16/13 10:17 PM

Quote:

Once again, you do what you want with your car.

I do not want a solid brake pedal.

Since you like the idea so much, why don't you run the numbers and tell us what kind of pedal arrangement and master cylinder it would take to get a 200 lb (since it doesn't have to be 300 lb) push on the pedal that generates no appreciable movement but still gives you 1000 psi at the calipers and between .003" and .008" of pad movement.

ok ,im not great at math so ill have to start easy.if i use a caliper as a mas cyl so the the volume is the same or four pumping into four if you like,a two hundred pound press should net 200 psi with no peddle leverage built in(push right on the mas cyl)

so if the peddle is one 14 long with two inches above the mas cyl that would be a force and distance multiplication of 6x so
1200 psi caliper press
.018 to.014 pad movement

thats about the closest i could come to putting it on paper i have no idea what cal volumes are and dont feel like doing pie.from my micky mouse setup it doesnt seem like 1000 psi and 1 inch of peddle travel is unreasonable,the problem is nobody in fifty years has put 200 psi in a brake peddle and most peaple are acostomed to tickling the peddle with thier foot and having thier modern brakes stop thier car for them.modulation to threshold is the job of abs so they dont need a hard peddle feel for modulation.

i like a soft peddle,heated seats,stereo,carpet,brakes that are bigger than my tires can justify- just like the next guy.

im also willing to push all that junk into a dumpster to go a little bit faster.ill even bother to listen to peaple like you who act arrogant toward me in hopes i learn something.

remember in the 80s when "pro street" cars were all over the place and thats what evryone was building.peaple saw cars like the silver bullit-ran tens in 1970 and was a street car and were inspired for the next twenty years to build cars that LOOKED like it.

fast foreward twenty years later and RJ GOTTLIEBs camaro catches the attention of the world outrunning evrything italy germany and japan could thro at it by a huge margin and set the car world on fire and for the next twenty years "pro touring" has done its best job to produce cars with the same "feel,vibe,penache,LOOK,ect,ect."

alot of these cars (like yours)remind me of the parade ground twelve second cars driving around with blowers sticking thru the hood back in the 1980s

Posted By: OzHemi

Re: My Big Brakes - 14"x1.25" with viper calipers on all 4 - 02/16/13 11:47 PM

Quote:

I don't have any Cayenne calipers but I've got a 6 pot unit off a Maserati.
Oh yeah, I've got a spare pair of 8 pot AMG calipers for the Imp.

You are welcome.

And my Torana combo works really well also (to me).... 8 piston Brembo front/360mm rotor, 4 piston Brembo rear/330mm rotor, and '00 Corvette master cylinder.