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Discussion Starter #1
Hey everyone, I'm looking for a little education here. I'm wondering what's more important when it comes to stopping power: Rotor diameter or No. of pistons/piston volume... I am looking into the future disc brake upgrade and have been looking at the 13" cobra upgrade using Mustang Steve brackets vs the 6 piston Wilwood set-up. Given the cost of some nice NOS cobra calipers, the total cost of the two setups seems similar. The obvious difference I see is that the Cobra brakes are 13" calipers with 2 pistons, while the Wilwood is 12.19" rotor with 6 pistons...

Ok, let the education (and arguing) begin!
 

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You must be considering some serious racing (Bigger rotors, bigger calipers), or a in need of the view aspect- Don't these look cool? or, My brakes are bigger than yours I have -----
If you want excellent brakes, do not to not install a complex, non stock, will fit made up parts--Why not install Bolt on, factory Mustang 4 Piston Disc brakes with 11 19/64" rotors.
These stopped all the Shelby's in 64 65 66 67 with superior results..
 

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It comes down to wanting between 900-1200 psi at the caliper piston. So you have to work backwards to master cylinder piston area to caliper piston area multiplied by pedal ratio. Bigger rotors and pads mean you'll displace heat better.
 

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Discussion Starter #4
You must be considering some serious racing (Bigger rotors, bigger calipers), or a in need of the view aspect- Don't these look cool? or, My brakes are bigger than yours I have -----
If you want excellent brakes, do not to not install a complex, non stock, will fit made up parts--Why not install Bolt on, factory Mustang 4 Piston Disc brakes with 11 19/64" rotors.
These stopped all the Shelby's in 64 65 66 67 with superior results..
First, let me say thank you for all you do for this forum and our classic mustangs - I have immense respect for you! And I do acknowledge that "cool factor" certainly influences some of my decisions, although my wallet has something to say about it too. I think your brake conversion kits are awesome - but am I that crazy to think there have been upgrades/improvements to braking technology in the past 50 years? I mean I'm not upgrading to headrests and 3-point seatbelts for the cool factor...These cars aren't the safest as it is, so anything I can to do improve the safety seems worth considering. If new brakes could stop me a few feet quicker than original style discs, that could make a big difference someday...

I also agree that readily available parts are a huge convenience, which is one reason I am looking at the '04 cobra brakes.
 

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First, let me say thank you for all you do for this forum and our classic mustangs - I have immense respect for you! And I do acknowledge that "cool factor" certainly influences some of my decisions, although my wallet has something to say about it too. I think your brake conversion kits are awesome - but am I that crazy to think there have been upgrades/improvements to braking technology in the past 50 years? I mean I'm not upgrading to headrests and 3-point seatbelts for the cool factor...These cars aren't the safest as it is, so anything I can to do improve the safety seems worth considering. If new brakes could stop me a few feet quicker than original style discs, that could make a big difference someday...

I also agree that readily available parts are a huge convenience, which is one reason I am looking at the '04 cobra brakes.
Again sir, it evolves back to what trips your trigger. If I can help in any why, please write, call.
 

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I'm running Kelsey Hayes style disc brakes as well, since 1998. Good stuff. Best advice I have is a dual-chamber master cylinder. No matter what your pedal ratio, bore size, power or manual, big rotor or not, piston size or count, slotted, cross-drilled or vented. None of it will work if you have a single chamber and it craps the bed.
 

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I’m interested to see the varied opinions on this topic. My thoughts are that today’s engines are making way more HP than the engines of that period. Even my mild 347 is putting out about 380 hp compared to 306 of the GT350 of the day. Seems to me that more braking force would be welcomed. Larger, slotted rotors are more for dissipating heat and are needed for road racing where the breaks are used a lot. More pistons can put greater and more even pressure on the rotor. I would think a better street set up would favor more pistons over larger rotors. But then again, I’m no engineer, so what do I know.
 

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In the case of these cars more braking power does not equal safer beyond a point, if that's your goal. These are comparatively light cars and it is somewhat easy to reach the friction threshold of most any tires. Same car, same tires, same road i doubt you could measure the difference in those 2 over a few episodes.
One thing for sure is that the 6 piston has a 3X chance over the other of a fault:love:

It ain't hard to skid these things and skidding is out of control and that ain't safe.
 

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The amount of horsepower or torque is what gets you to a speed and keeps you there, but has little to do with what stops you again...
306 Hp in 1965 or 400 Hp in 2019... in a 3000lb car moving in a straight line in either the right or wrong direction will take the same amount of energy to stop today as it did then. The laws of physics haven't changed. What HAS improved is tire technology, suspension that keeps those planted, and yes, some brake technology. I haven't seen anybody get front/rear ABS retro fitted on an otherwise first gen Mustang, so ya gotta plan what you're gonna do with the car, buy the parts you need to stop it in those conditions, and learn how threshold braking works. It's more of a matter of bells-and-whistles brand preference beyond that.
 

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...but am I that crazy to think there have been upgrades/improvements to braking technology in the past 50 years?
Pretty much the answer is "No, you probably aren't crazy but, then again, there really HAVEN'T been any upgrades/improvements to braking TECHNOLOGY in the past 50 years."

Disc brake systems consist of a rotor, a friction material (pads) and a caliper to apply pressure to drive the pads into the rotor. There are more different varieties of rotors, calipers and pads than there are flavors of Campbell's soup but they all do precisely the same thing.

The bigger and heavier the car, the bigger the brakes. The smaller and lighter the car, the smaller the brakes.

Properly installed, serviced and maintained, the original K-H brakes with 11.3" rotors and D-11 pads will lock the front wheels in a panic stop at just about any speed you can get to short of a racetrack. Also to note is that the K-H 4-piston setup is maybe a hair superior to the later single-piston floating units used in stopping power and those later brakes came on all the FE and 385-series cars.

FWIW, you can have a 8-piston, 15-inch rotor hydroboosted system that is the next best thing to sliced bread but if you can't put all that braking power down to the pavement (meaning you easily lock up the wheels whenever you jab at the pedal) what good is it?

Anyhow, to answer your "stopping power" question, it's all about the amount of friction you need to generate to stop the mass of rotor, tire & wheel spinning against the forces driving it.
 

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Speed limits were also 55mph back then too where as they are up to 85 here today and general cruising on the freeway now is 70mph minimum here. Many new vehicles today have big rotors front and rear and even most those really don't have enough braking ability.

A brake pad the size of a pencil eraser is enough to stop a car. The reason cars have bigger rotors and pads is to reduce fade. And with modern tires with better compounds and more footprint they can take much more braking power today than in the past. Tire and brake technology has changed allot in 50 years. Sticking with old calipers and small rotors is like sticking with a stock 289. There is a place for a stock type brake system but many want to upgrade and improve their braking right along with their engines etc.
 

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The 55 MPH law became effective in 1974, a full 10 years after the Mustang was introduced.
That was a federal overruling of all state imposed speed limits. Before that they varied from roughly 55-65. Which is even more scary driving cars with crude brake systems etc at those speeds. Luckily Nevada finally went after the law and got that changed as it was being used as a method of extortion against the states IE your people drive faster than we want them to then we take away funding. It's also the hotel and gas station lobby that wants to keep speed limits lower because it increases their business as it takes longer to travel so you need more snacks drinks and it takes more nights on the road.
When we moved to TX from Hawaii (worst trip of my life and still stuck here) we had to drive from San Diego as that's where they dropped the car off the ship. That was a really really long drive at slow speeds. San Diego was a scary place... The parking lot at the hotel was surrounded by 12' fences and concertina wire and we got stuck there for 4 days as they took the car off at the wrong port and had to trailer it to us.
 

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Frist, as others have said, the original front disc brakes can lockup the tires no matter what speed you’re doing short of the track. So, for street driving the K-H or later single piston brakes with a good pad are all you really need. The back of these cars is so light that the drums are sufficient for the street - but you can get the bigger 11" drums if you can.

Second, the larger diameter discs can handle more abuse, i.e., racing. The modern car must meet safety standards that include multiple stops from highway speeds. Unless you envision having this situation it is over-kill.

Third, to answer your question “what's more important when it comes to stopping power: Rotor diameter or No. of pistons/piston volume” the answer is both. Consider that the pistons push on the pads a certain distance from the axle center line causing a braking torque. The further from the center line the greater the torque for the same “push.” The area of the pistons determines the amount of “push.” Whether one piston on a sliding caliper or four/six pistons on a fixed caliper, simply determine the total area of the pistons on one side. The more area the more push and thus the more braking torque. Also, thicker/wider discs will be able to absorb more heat before you notice fade from multiple stops.

Lastly, you might consider aluminum calipers to save weight (and un-sprung weight at that). I’ve toyed with the options from Street or Track. http://www.streetortrack.com/Brake-System-Quick-Guide-p-11.html
 

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My 70 has front disc and rear drum.
When I was looking into upgrades for front and rear disc it was recommended that I just go with improved friction materials and keep the stock setups.
And if you can, go with slotted rotors, don’t bother with cross drilled. All the drilled rotors do is reduce some weight.
 

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I drive my car hard, and the best thing about the big brakes is improved resistance to fade (as many others have mentioned)

I picked up the 13” x 1.25” front discs from SoT. Four piston calipers. Very happy with them over the last two years.




Sent from my iPhone using Tapatalk
 

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A brake pad the size of a pencil eraser is enough to stop a car.
This is EXACTLY CORRECT. A pad this size will not stop it very many times though. They are much larger to provide service life.

The reason cars have bigger rotors and pads is to reduce fade.
Repetitive braking without exceeding the thermal limitations of the system (i.e.: that friction compound's specifications when used with the heat
dissipation capabilities of the rotor).

For the OP..... caliper clamping force and friction material capabilities are the main things that determine stopping power. (tires are right up there too)
If you want to stop at the limit repeatedly, rotor mass is also critical.

ex-Global West GM
1991-1995
 

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Speed limits were also 55mph back then too where as they are up to 85 here today and general cruising on the freeway now is 70mph minimum here. Many new vehicles today have big rotors front and rear and even most those really don't have enough braking ability.

A brake pad the size of a pencil eraser is enough to stop a car. The reason cars have bigger rotors and pads is to reduce fade. And with modern tires with better compounds and more footprint they can take much more braking power today than in the past. Tire and brake technology has changed allot in 50 years. Sticking with old calipers and small rotors is like sticking with a stock 289. There is a place for a stock type brake system but many want to upgrade and improve their braking right along with their engines etc.
The speed limit on the Atlantic City Expressway in the fifties and sixties was 70 mph, as were many other freeways and in many Western states there was NO speed limit. The vast majority of the cars at the time were running 4 wheel drum brakes. The reason for BIGGER rotors and calipers is that the cars are HEAVIER. The original Mustang tipped the scales at around 2950 lbs. The 2019 GT weighs 3,750 lbs. That's over 20% more weight for which the braking power requirement is exponential the faster you go. That said, there's no reason to NOT upgrade your braking system IF you need to do so.
 

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KH discs and quality D11 pads were an upgrade on my 66. Still happy with them 22 years later. Made a huge difference in my safety and of those around me over the drums when it was raining. Also, a whole hellofalot easier to change a set of pads than rebuild a set of drum brakes with shoes.
 

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I used the Mustang Steve 2008 GT brackets with 12.4” EBC rotors and red stuff pads. It has a little bling but the main goal was to not use Chinese parts.
737594
 
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