rear disc brake line pressure?

Ok i'm getting a rear disc conversion for my 65 mustang.
It has front disc already w/ the factory prop. valve. Can I still use this or do I need to get a adjustable prop valve? I believe disc's require more line pressure so I was not sure if my factory valve will be enough. Also anyone having any brake line issues when doing a conversion?

Drums require more pressure. Discs require more volume, not necessarily more pressure. Most Ford master cylinders have a 2 step bore, one large bore for the front discs and a smaller rear bore for drums....but the smaller bore makes a spongy pedal and the calipers won't work as they're intended to.

I use a '79-'93 Dodge 1/2 ton pickup master cylinder. Had to cut/shorten the pushrod and drill the 5/16" mounting holes out to 3/8"...and make new fittings. Works way better than anything else I've used, including a high $$$ Wilwood M/C that was "supposed" to be the "one" for my setup...guy was wrong. The bias valve should be fine. I am still using my stock one that was set up for drum/drum.
[addsig]

You did not mention were your getting the conversion from?
the propotioning valve is very important...
I'm swapping the discs from a 70 lincoln into my
77 Ranchero...a stright swap with the axles, rotor,calibers,
and change out the proportioning valve...
this is a 9 inch Ford rearend...
so one answer is no you can not use the stock valve..
Best

Thanks, I got the SSBC rear conversion for the 8" rear, also got their
adjustable prop valve. I hope this will work nicely......