WHO'S GOT THE SCOOP ON RESIDUAL VALVES?

[Bewy]

I can tell you this: my car came with 4 wheel drum brakes, which are still on the car. I removed the single m/c & replaced it with a late model [ early 2000 model ] dual m/c. This m/c was used with 4 wheel disc cars & did NOT have RLPVs. I also have the auto brake adjusters working. My pedal moves about a 1", maybe 1.5", & I have a rock hard pedal.

 

[Mattax]

Residual pressure in drum brakes is to maintain load against the return springs on the shoes. Removing it from drum brakes causes an increase in fluid needed to apply the brake. It causes spongy brakes and for front disc cars the appearance of no rear brake at all.
Under normal driving you wouldn’t miss the rears. In a panic stop you will know they aren’t there.
Original master was 1 1/32 and are available new on rock auto and other places. Guys all over FABO discuss the right master cylinder for your car in detail. Please read them. Lots of great advice. Smaller cylinder means more travel but lower pedal effort. I’ve used the 1 1/32 master on all of my manual disc brake cars and liked the feel. Currently they cost around $60.
For your safety though don’t eliminate RPV on drum brakes. It is necessary. On the other side it causes disc brakes to drag so it shouldn’t be on a disc.

I used to think that too, but its more about keeping the seal.

1970 Chrysler Imperial Hydraulic Brake Service Guide from the Master Technicians Service Conference Session 274

If the 15 psi really helped keep the linings close to the drum surface, then we wouldn't have to keep adjusting them to compensate for wear.

 

[Killer6]

Yup, I got all that. Just trying to figure out if this new master needs one when using the wheel cylinder rebuild kits I am using. (see post 19)

I know of nobody manufacturing new wheel cylinders the 'old' way, so residual check valves are redundent, it won't hurt You to have one....but it doesn't matter to You if everything is working as designed & You've got clean fluid in the system. Put it together & gett'er bled.
I did have a new wheel cylinder that refused to bleed, I put both on a late '70's TransAm, the Passenger side would bleed...but if I waited 15-20seconds,..it would burp more air when bled. It was letting air suck back in, spreader was probably missing,......but hilariously, it belonged to the Advance Auto Parts store Manager & brought His own parts..lolololol, He had to call the store & have them send another, which bled fine..peace!