Residual pressure requirements are different for discs and drums (I believe 10psi for discs and 2psi for drums). Residual valves can be purchased to install in your brake system. If you plan to run drums in front for a while, be careful when you get your dual master. If it comes from a vehicle with front discs, it may have a 10psi valve built in (and maybe a 2psi one as well).
Also, if you are worried about interaction between fronts and rears from different eras, get a proportioning valve to fit in the rear brake line. You will be able to reduce the pressure to the rear brakes and make sure they won't lock up before the fronts.
Current fleet (subject to change w/o notice) \'49 GMC 3/4-Ton , 60 Austin Healey Frog-eye Sprite (some assembly required), 2011 Dodge Avenger, 2015 Jeep Cherokee. No, they don't all run. My other ride is a (B737)no, (B767)no, A320.... Update... was Embraer E190, now Boeing B787. Knowledge is a wonderful thing, but ignorance means you don't know you can't do something.
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