1968 4 piston front disc brakes

[pnandy]

how much should i be paying for a complete set of these that are in working condtion? found some on craigslist right next to me came off a 1968 mustang gt fastback, i have 14 inch torq thrust in the front to so these have the right size discs for me

[Waffles]

$700 sounds fair to me, though it's always easy to spend someone else's money.

[pnandy]

hmm then 350 should be just fine  ~h2

[Waffles]

Sure, especially if its all in good condition. What all is he including???

[Fast68back]

Yeah, even if they are shot you can use them for cores as rebuilt ones are around 100 a piece, IIRC

[pnandy]

I've talked with him for about an hour he is getting his 68 painted needs money he upgraded to bigger brakes and doesn't need these  he said it comes with everything that i will need for the conversion short of brake lines they are what he was using a couple months back on his.    called him and plan to pick them up this sunday

[Waffles]

Congrats. You just made out like a bandit. Post pics on sunday

[Starfury]

Interesting.  To my knowledge, 68's didn't come with 4-piston calipers.  KH-style 4-piston calipers were only used from 65-67.  68+'s got single-piston floating calipers.

[pnandy]

even if it was a early production 68?   maybe they were taken off a 67 prior to his?

[Starfury]

I suppose it's possible.  I don't know enough to claim that it's not.  I don't believe you can swap 67 to 68 brake parts like that, though, as I believe the spindles are different.

Either way, I think you got a deal.  If it's for a 67 and won't work on yours, you can clean them up and sell them for twice what you paid.  If it's for a 68, you've got a new set of brakes:)

[cmayna]

yes, I believe 4 pistons ended with 67.

[shbrandt]

I bought 4 piston disc brakes from a 68 Fairlane for about $400, plus shipping. They came with the spindles. However, they required a booster unit as they were for a power brake car. They work just fine.

[Laurie S.]

1968 Mustangs did not have 4-piston front disc brakes, only 2-piston.  I got a set of the 67s for my fastback.

[pnandy]

ya i went to take alook at them and they weren't in good shape so i decided ot go with the csrp 4 piston front disc brakes for a 68 and ima do the crown vic disc's in the rear on my 9 inch rear

[cmayna]

Laurie,
Are the 4 pistons better than 2 piston?   Is this why you changed over?

[Laurie S.]

Well, we figured that since there was twice as much gripping surface, it wouldn't hurt.  My fastback didn't have disc brakes at all originally.  Probably why it was in at least three accidents before being torched.

[monkeystash]

Craig and Laurie,

The '68 calipers are 1 piston, not 2.  They just have 1 piston on the back side, which is called a floating caliper.  I have these on my Fairlane and they seem to work just fine.  Here's a picture of mine.

[Starfury]

The pad area isn't actually any greater on the KH 4-pistons.  The advantage is that the calipers are heavier and static mounted, and therefore will absorb more heat.  I believe they also have a larger piston surface area, which means more pressure on the pads.

[gt289]

Pad area really doesn't affect anything other that brake pad longevity itself. (Bigger the pad the
cooler it runs. Cooler it runs the longer it lasts)
Caliper clamping force determines who's gonna stop first (provided you've got the tire to do it).
Rotor size determines how many repetitive times you're going to stop effectively before heat
becomes an issue for the brake pad formulation.

[Starfury]

Not true.  Stopping power is a function of friction area, pressure applied, and the coefficient of friction.  Increase any one of those things and you'll increase stopping power.  That's why drum brakes have equal stopping power to most disc brake systems.  Applied pressure is low, but swept area is much greater than in most disc brake systems.

You can make up for less swept area with more pressure, although (as you stated), the pads will tend to run hotter.  That's the advantage of the KH 4-piston calipers, which run cooler because they have more mass and are mounted to the spindle, which allows for better heat transfer.  Floating calipers do not directly contact the spindle and don't transfer heat well, especially on the outside pad where there isn't much caliper mass.  The larger swept area makes up for the reduction in applied pressure and helps keep pad temperatures manageable with the floating caliper design.

I have OE-style KH calipers on my '67 and I love them.  Although something in the r/f is leaking now.  I hope it's not a caliper seal:(  One downside of 4-piston calipers is that there's more stuff to go wrong.

[gt289]

Stopping power is a function of pressure applied, and the coefficient of friction.  Increase either one of those things and you'll increase stopping power. 

Now it's a correct statement. Swept area, contrary to popular opinion, does not have a bearing
on stopping power. (period, end of sentence)

Brake pad geometry (height, width, surface area) does not influence the gain in a brake system.
(gain relates brake system force input to brake system force output)
Bigger pads do not stop any better than smaller pads.


Don't believe it? As Randall Shafer (StopTech) likes to say "pad material coefficient of friction
is independent of the size of the pad itself. Installing larger pads may increase the life of the
friction material, but there will be no difference in brake system gain." (page 91, "High Performance
Brake Systems" by James Walker Jr.)

The reason why drum brake systems stop so well is not a function of their large swept area
(when compared to most disc setups), it's mainly because most drum systems are self-
energizing, so you actually get mechanical assist that is not present in a manual disc setup.
The drum system's downfall is in hard, back-to-back repetitive stop situations, where thermal
issues become a really big problem, really fast.

Before I worked in the brake industry, I used to think swept area was king, myself. I got
schooled pretty quickly, much to my chagrin (and embarrassment).

[AtlantaSteve]

gt289, thank you for explaining that.

I have heard time and again about changing pad sizes to affect stopping force and could never figure out the math of how that would work.  In my physics classes we always calculated friction as being a function the coefficient of friction and the force applied, but surface contact area never was part of the equation.

It was a law of the universe.

And then I got into cars and would hear of people cutting down pads to make them stop better and was like "Is physics wrong?  Or does it take a break in a braking system?"

But it was such common knowledge that I assumed there were additional variables that I didn't understand.

That said, I'm sure there will be disagreement. I believe this might be as tightly held a belief as the notion that .99999... Does not equal 1....Mathematically, they are identical, but people refuse to accept this, and will fight you over it.

[Laurie S.]

While we're on this subject, I just removed the 1968 spindles and 1967 4-piston disc brakes from Trouble and replaced them with Baer brakes.  I want to sell these but am wondering what they are worth?  They come with stainless brake hoses, also, and there is probably less than 5 miles of use on them.

[Starfury]

Hrm.  Interesting.

[SAC69]

So, if sweep area is irrelevant, (if I am understanding the logic here), it does not make sense for someone to upgrade the rear drumns from 1 3/4" to 2 1/2" size?