Brake Sizing Advice

[Handy Man]

On my '66 Mustang I have the stock Kelsey Hayes style disc brakes in front. I'm trying to find a rear disk brake setup that will be well balanced. The two best options I've found seem to be Wilwood or 94-98 Cobra brakes. Looking at piston area and caliper size the Wilwoods appear to be too strong, and the Cobra's appear to be way too weak (due to being single piston). Am I missing something here? Can a proportioning valve cut down the pressure enough to balance out the Wilwoods?

Current Front:
Kelsey Hayes - 4 x 1.625" piston calipers with 8.3 in^2 total piston area and 11" rotors

Rear Options:
Wilwood 140-7143 - 4 x 1.38" piston calipers with 6 in^2 total piston area and 12.2" rotors (if my calcs are right, this will result in front/rear brake torque split of 58/42)
94-04 Cobra brakes - 1 x 1.5" piston calipers with 1.76in^2 total piston area and 11.65" rotors (if my calcs are right, this will result in front/rear brake torque split of 83/17)

[a67]

With calipers that have pistons on both sides, only one side counts. So the Kelsey Hayes front calipers are 4.14 sq/in of piston area.

If the 94-04 Cobra calipers are floating and the Wilwood are fixed, I'd go with the floating Cobra calipers.

Bob.

[Apogee]

X2...the Cobra brakes should match up nicely with the stock KH fronts assuming a typical front/rear weight bias on your '66 Mustang.

If you were to look at Wilwood kits, they offer their FNSL4R kits with a 1.98 square inch effective piston area that would be a good choice. You should be working with a Ford 8 or 9 inch rear end, so fixed versus floating isn't as much of a concern in your application IMHO, especially if you're running power brakes, not manual.

Tobin
KORE3

[Handy Man]

Thanks guys. I must have had a brain fart for the calipers with pistons on both sides. Apparently I've forgotten everything I learned in engineering school.



Whats the advantage/disadvantage of floating vs. fixed? From what I've read it sounds like fixed has better pedal feel but floating is less prone to knock back. I have manual brakes now, and plan on staying that way to at least test out the pedal effort with manual 4 wheel disks. If effort is still higher than I like, I'll add a booster later. And yes, I'm running an 8" rear.

That FNSL4R caliper looks awesome, but it doesn't look like it will fit under my 16" wheels.

[a67]

Whats the advantage/disadvantage of floating vs. fixed? From what I've read it sounds like fixed has better pedal feel but floating is less prone to knock back.

It is the pad knock back issue with fixed calipers that I recommended the floating calipers. There are quite a few posts here from folks that have had knock back issues. Even with non-c-clip rears.

The other way to go with fixed Wilwood calipers (or others) is to float the rotors.

Bob.