[Healeys] Brakes -rear wheel cylinders

[Bob Haskell]

Listers,

The rear wheel brake cylinders are 1" diameter on the 100 and 100-6. 
When the disc brakes were introduced on the 3000 MkI, the  wheel 
cylinder diameter changed to 3/4".  So if one is fitting a 3000 disc 
brake set up to an earlier car, should the rear cylinders be swapped out 
too?

If I'm doing the math correctly, the force on the brake shoes with the 
smaller cylinders will be 56% of the force with the large cylinders, for 
the same hydraulic pressure.

force = pressure * area
area = PI * (dia / 2)^2

1" cylinder -> area of 0.785 sq. in.
3/4" cylinder -> area of 0.442 sq. in.

0.442 / 0.785 -> 0.562 or 56%.

Cheers,

Bob Haskell
Austin Healey 3000 MkI registrar
http://www.ciahc.org/registry_3000mk1.php