Matching rear brakes to the front

[fordsbyjay]

I have a 13" Brembo kit from Vintage Venom on my 64 Falcon and I am looking for some rear brakes now. They make a rear kit using the Cobra Mustang rear setup as well but I don't understand why they use such a small caliper in the rear. Did Ford use the same rear setup on all the Mustangs or just the Cobra's? I understand that the rear brakes only do 30% of your braking but it doesn't make sense to me to put 13" 4 piston Brembos on the front then a single piston deal on the rear. Is there a better recommended setup to match my fronts?

vintage venom link here (http://vintagevenom.com/)

[a67]

Yes it makes sense. As you mentioned the rears do a smaller portion of the overall braking.

As an example, use 13" diameter rotors front & rear, and the same pad compound front & rear. This negates any differences from pad coefficient of friction and the lever arm length on the rotor.

Use front calipers with 3.53 sq-inches of piston area (two 1.5" dia pistons).

And rear calipers with 1.18 sq-inch of piston area (one 1.2" dia piston).

Note that 1.18 sq-in is 1/3rd or 33.3% of 3.52 sq-in. And the above values are rounded.

Applying the same line pressure to the front & rear and the rears have 33% of the braking force as the fronts.

And the rear calipers are much smaller then the fronts with 1/3 of the piston area.

Before deciding on which rear brakes to get calculate the piston area of your front calipers. Then calculate what range of piston area is required for the rear brakes. Note that items such as vehicle front/rear weight bias also affects the amount of rear braking.

These should be sized more then 33% of the fronts as you can back down the pressure some with a proportioning valve. That will allow you to tune the front to back brake bias.

For more information on this and other aspects of braking systems check out stop tech's web site. They have a lot of good information on how this all works.

Bob.

[xpsled]

I am going through this issue at the moment on my 1965 Falcon Coupe. Be very careful running a multi piston style caliper on the rears without a full floater diff. As the flanged axle moves under hard cornering it knocks the pads back into the caliper and then when you push the pedal your first couple of inches of travel there are no brakes, not even fronts as all that fluid is just moving the pads back towards the rotor.
Just something to think about!!!!

[Bryce]

Great point xpsled.

Also decide what kind of parking brake you want. Wilwood has a single floating aluminum caliper with an integral parking brake in the caliper. Otherwise you need the drum stye inside the rotor.

[fordsbyjay]

Yes it makes sense. As you mentioned the rears do a smaller portion of the overall braking.

As an example, use 13" diameter rotors front & rear, and the same pad compound front & rear. This negates any differences from pad coefficient of friction and the lever arm length on the rotor.

Use front calipers with 3.53 sq-inches of piston area (two 1.5" dia pistons).

And rear calipers with 1.18 sq-inch of piston area (one 1.2" dia piston).

Note that 1.18 sq-in is 1/3rd or 33.3% of 3.52 sq-in. And the above values are rounded.

Applying the same line pressure to the front & rear and the rears have 33% of the braking force as the fronts.

And the rear calipers are much smaller then the fronts with 1/3 of the piston area.

Before deciding on which rear brakes to get calculate the piston area of your front calipers. Then calculate what range of piston area is required for the rear brakes. Note that items such as vehicle front/rear weight bias also affects the amount of rear braking.

These should be sized more then 33% of the fronts as you can back down the pressure some with a proportioning valve. That will allow you to tune the front to back brake bias.

For more information on this and other aspects of braking systems check out stop tech's web site. They have a lot of good information on how this all works.

Bob.

I have 4 piston Brembo's with 36/40 mm pistons.

By my calcs in sq in's it would be 1.4173 / 1.5748 for a total of 3.16in² and 3.90in².

[a67]

I have 4 piston Brembo's with 36/40 mm pistons.

By my calcs in sq in's it would be 1.4173 / 1.5748 for a total of 3.16in² and 3.90in².

OK, if there is a 36 mm and a 40 mm piston on each side, then the effective area of the pistons is:

(36 / 2) ^ 2 * Pi = 1017 sq-mm
(40 / 2) ^ 2 * Pi = 1256 sq-mm

Convert to sq-in:

1017 * 0.00155 = 1.58 sq-in
1256 * 0.00155 = 1.95 sq-in

Only one side is used as the pistons oppose each other. Keep this in mind when doing the calcs, only one side of the caliper is used for clamping force.

Total of 3.53 sq-in of piston area contributing to the clamping force.

Which matches the example I gave (surprisingly, as those numbers are from a PBR caliper). Now just need to match up a rear caliper. Can use a dual piston (opposing) Brembo with a 1.2 to 1.4" pistons. Or a floating single piston caliper with the same (1.2 - 1.4").

If you use a rotor that is different from 13" in diameter, then that will need to be taken into account on caliper piston area.

I checked out your car, nice. And since there are dual master cylinders this gives another level of adjust-ability. Can change the M/C bore for more or less pressure and more or less available fluid.

Bob.

[fordsbyjay]

Only one side is used as the pistons oppose each other. Keep this in mind when doing the calcs, only one side of the caliper is used for clamping force.

Total of 3.53 sq-in of piston area contributing to the clamping force.

This makes a lot more sense. I was coming up with double that.


I checked out your car, nice.Bob.

Thanks,

I will see if I can find out what size the rear cobra calipers are. I am kind of leaning towards a Wilwood setup in the rear but I would kind of like a matching system.

[Bryce]

Jason,

What did you decide?