Do I really need a residual pressure valve?

[SD455]

Just getting ready to plumb the master cylinder on my 65 GTO. Car is a stock looking restoration, I have upgraded to D52 calipers in the front, stock drums out back. The master I am using is from a 77 Malibu manual disc brake application 15/16 bore( would the residual pressure valve be built into this disc/drum master?). I'm trying to keep the install as clean as possible and do not want any visible proportioning valve, or residual pressure valve visible from the engine bay. This has me wondering, are they even really necessary in a street application considering the combination. I'm using EBC " Yellow Stuff" pads up front which I think are rated at FF so they should provide some pretty good front bias, and if I recall correctly the last time I had run the proportioning valve on this car is was set wide open.

Anyways, I am definitely not a brake expert, so would like some advise on this topic.

[F-Body International]

Are you referring to have the valve for rear drum brake applications?

[79 Camaro]

I think the only time a residual valve is used in the rear brake line is when the brake master is lower than the brake cylinder like on a lot of street rods where they are mounted under the floor.
I do think you should have a proportioning plumbed into the rear line. It can be mounted under car to keep it out of site.

[dontlifttoshift]

All drum brakes require a residual pressure valve. Period. Without pressure on the cup seals in the wheel cylinders, the system will draw air in.

Whether that valve is plumbed in line or installed in the master cylinder is up to you.

[SD455]

All drum brakes require a residual pressure valve. Period. Without pressure on the cup seals in the wheel cylinders, the system will draw air in.

Whether that valve is plumbed in line or installed in the master cylinder is up to you.

How does one go about determining if there is one already within the master cylinder? Is it safe to assume a factory replacement master cylinder for a factory disc/drum car would already have one?

[dontlifttoshift]

It's spring loaded rubber check valve behind the brass flare seat in the master cylinder. You can poke in there with a paper clip and feel it and sometimes you can even see them.

All drum brake master cylinders should have them, all disc/ drum master cylinders should have them in the rear circuit.

I always plumb them inline, it doesn't hurt to have two, and it future proofs the system.

[RobNoLimit]

I go further than Donny. Simple rules. 1) Always install check valves in front and rear. 2 lb for disc, 10 lb for drums. (yes, always) 2) Always install an adjustable proportioning valve in the rear line. 3) NEVER use a metering block. ** these rules are for custom builds. 100 point restorations do not count. ** Every car or truck, every time for the last 30+ years. Quick brakes, no headaches, life is great.