disk brake master cylinder

[flyinlow]

I installed rear disk brakes on my 73. The kit uses 11 inch vented rotors and Cadillac single piston rear calipers. Used the stock master cylinder and remover the perportioning /metering valve. The brakes stop well, but the petal is lower than it was with the rear drums. Do four wheel disk require a different master cylinder?

Have bled repeatedly , even tilted the rear calipers to make sure there was no air trapped as we bled them.

[John_Kunkel]

The larger pistons in the rear calipers will require more fluid volume so you'll need a MC with a larger diameter.

[flyinlow]

The car has the 4 bolt 1.032 inch mastercylinder.  I have seen 1.25 inch late model aluminum and plastic ones ,but they are 2 hole mastercylinders.

[Mefirst]

Changing out the MC to a larger displacement one may give you a really rock hard pedal.. There is a "band aid" you could try before changing out the MC, try mounting a Residual Pressure valve on the rear brake line..

http://www.summitracing.com/parts/WIL-260-1874/

Also try different Proportioning valve settings...

/Tom