Another Disk brake conversion question

[Dave22443]

1968 Dodge Charger - 4 wheel drum, non power brakes.  Purchased a disk brake setup off ebay (brand unknown - but looks like stock brakes would).  Also purchase disk/drum proportioning valve.  All parts installed and fit well (no clearance issues or line problems).  Have been bleeding and bleeding and can get pedal pressure, but only after many pumps.  Rest a minute, pedal goes straight to the floor again.  I've run about 4 small bottles of brake fluid through the lines but get no immediate pedal pressure.  Have to pump many times to get brake pressure.


Question: Do I need to also change the master cylendar to a disk/drum type?  Or will my original drum/drum work?  I've read stuff here and online but it doesn't seem clear to me.  Looking for a difiniative answer from those in the know.   Thanks!

[Troy]

So now you have front disks and rear drums?

Troy

[Dave22443]

Yes.

[bull]

Yes, you need a disc/drum master and either a 10 psi residual pressure valve or newer rear wheel cylinders with cup expanders. Disc brakes and drums brakes operate off different pressures and you need to regulate that somehow.

http://wilwood.com/Products/006-MasterCylinders/010-RPV/index.asp

[BrianShaughnessy]

If getting new rear wheel cylinders...  consider the smaller 7/8" bore versus the stock 15/16" to change the proportioning.    Old Mopes have too much rear brake bias if you're running a stock type prop valve.   I just recently did this because I totally forgot about it and I was fighting a low pedal problem.
37236 was the interchange number - they came on 70's/80's trucks and 60's C bodies.   Yeah, they cost more.  Whatever.