Quote:

Quote:

He's probably close - The thing is, and what each hot rodder needs to figure out for their specific situation, is how much the brake system's balance has been altered. This is when it's worth getting a good book (like Carrol Smith or Fred Puhn's Brake Handbook) and going over scenario on paper.

For example, lets look at someone swapping front calipers. Lets ignore the disk diameter and just look at hydraulics. A stock '69 B-body would have come with Bendix calipers that had a total of 4, two inch diameter pistons. This equals 12.59 quare inches. Now how does that compare to the area of the calipers being changes too? How much difference in force applied from the stock system? This is the type of pencil and paper work that will reveal whether more or less master cylinder pressure may be needed to get the pad forces needed.

Back to the OP's Master Cylinder.
Hydraulic pressure = Force on piston from pushrod / Area of piston
1" piston, Area = .7854 sq inches
1 1/32 piston, Are = .8353 sq inches
1 1/8" piston, Area = .9949 sq inches

Therefore, for the same pedal force, we can see the effect of each of these on system pressure.
Lets say a gentle pedal puts 100 pounds force on all three piston sizes. The 100 pounds force in this example is at the pushrod, the foot is applying a lot less than that to the pedal. How much less depends on the pedal ratio - a number I don't have off-hand.

1" piston => 127 psi
1 1/32 piston => 120 psi
1 1/8" piston => 100 psi

You can see that changing to a 1" master cylinder from the 1 1/32 master that the OP already has, will make only a slight difference in pressure in the system for the any given foot pressure. Even if he stands on the brake pedal and puts 500 pounds into the pushrod, the difference in hydraulic pressure will be 600 vs 635 psi.



The later model calipers all have pistons that are about 2.75" diameter ('76 Cordoba), the area being roughly 6 inches ... half of the stock '69's !!

That said, using the same system but with the later calipers it would take less pedal to compress the piston BUT with less area it requires more pressure. Therefore, you'd want a smaller bore m/c which would take more pedal but be applying more pressure for the same effort.

This is all fine and dandy for disc to disc conversion but drum to disc conversions are a whole different ball of wax.



That's a misconception, the 4 smaller pistons aren't 2x the single big piston.

You only use 2 of the pistons, they are pushing on each other.
4 piston Area = Pi*R^2 = 2*(3.14 x 1^2)= 6.28
Single piston = 3.14 x (2.75/2)^2 = 5.94

Less, but not 1/2 as much