Residual pressure valve on drum/drum boosted car?

[Fabulous50s]

Finding all kinds of conflicting information regarding the use of residual pressure valves on cars with the master cylinder in a stock (higher than the wheel cylinders) location. Some say the valves are needed, some say only if master is below brakes, blah blah blah!

I've got all new brakes, lines, wheel cylinders etc. An aftermarket 1-1/8" dual master with 8" dual booster. Are the 10psi valves needed to "take up slack" or "to keep the wheel cylinder cups inflated"?

I was a mechanic for 10 years and all we ever worried about was proportioning valves! Supposedly residual pressure valves are built into factor proportioning valves?

Also, I assume for a drum/drum car no proportioning valve is needed.... there certainly wasn't one from the factory, but we are now over 60 years later and I'd like it to be better than factory.

Thanks for the first hand experience this site offers, with our classics.

[RICH MUISE]

I may be wrong, but I believe the residual valves are needed on a disc/drum setup, and the proportioning valve (what I've got) is for disc/disc.

[hiball3985]

Residual valve is needed on drum/drum. Residual valve only on rear if front is disc. If you changed to a dual master and be sure it is from a drum/drum car. Or add them inline front and rear.

[Ford Blue blood]

I'm going to have to be a little contrary here.  Many new master cylinders have a residual valve built in them.  Adding one in line would be just a source for future leaks and problems.  Wheel cylinders that don't have springs inside them need the 10 lb valve.  That is to keep the cups up tight against the cylinder walls.  As long as the master is above the wheels no additional valves should be required. 

The metering block serves two purposes, controlling rear brake pressure and preventing a complete loss of brakes if either a front or rear line should fail.  There are very few "true dual" master cylinders out there.  The modern master is co-dependent on each half to seal and build pressure.  Pull one apart and you will see only three seals in there, a true dual will have four with a spring between the rear and front portions.

Given all the various myths/rumors/urban legion's out there about brake systems I use the complete system from the donor car and do not "re-engineer" any part of it.  I also only purchase complete after market systems designed for a specific application.  Never had one that didn't stop like it was supposed to.....

[hiball3985]

Yes, many of the early masters have built in residual valves, but I have run across later model ones that don't, thats when you need to add them inline. I agree not the best method..

[Fabulous50s]

My master does not have the valves built in. I was just thinking I'd rather plumb them in now rather than get brake fluid all over stuff by adding them later if they are actually needed.

I have no metering block, was planning on running the rear line (closest to the firewall) just to the rear brakes. The front line out of master to a T to each front wheel cylinder. Also have a T with brake light switch in there somewhere.

Considering all stock is a bunch of Ts from the master to all the wheels.

Does a metering block add any advantage to a stock drun/drum system. If I am not happy with the front drums, I'll convert to disc at a later time.

[Fabulous50s]

So I should get two residual pressure valves, 10psi for drum brakes? What do you guys run? Or are most of you using a stock master cylinder for a drum/drum car? Mine is 1-1/8", but it is an aftermarket kit.

[gasman826]

Since I've had my c-19 medication (Southern Comfort), I'll step into this **** storm.  If aftermarket means Wilwood or Baer, these master cylinders have no check valve.  Most high end masters will list whether they have a check valve or not or what size if the do.  If aftermarket means some OEM knockout kit off eBay, it will likely mimick the OEM that is knocked off from.  Some later model OEM masters have no check valves but are in the proportioning valve.  You have to know where your system is coming from!  If using a Wilwood master, check valves could be required.  Wilwood says that if you are having problems, add check valves even if your master cylinder is higher than your wheel cylinders.

[KULTULZ]

Finding all kinds of conflicting information regarding the use of residual pressure valves on cars with the master cylinder in a stock (higher than the wheel cylinders) location. Some say the valves are needed, some say only if master is below brakes, blah blah blah!

Not unusual as many have different ideas and theories (even kit suppliers). Yes a residual valve(s) (#10lb) is needed on older drum brake applications. On the single reservoir MC, the valve was in the MC. Later two reservoir had the valve(s) in the outlet port(s). Some designs had them on the proportioning/combination valve (GM mainly). Modern designs do not use one at all (different design MC) (FORD stopped using a RPV at he 1971/72 model run and used wheel cylinder cup expanders in the drum brake wheel cylinders).

If you have a new aftermarket MC, it will not usually have an RPV(s).

I've got all new brakes, lines, wheel cylinders etc. An aftermarket 1-1/8" dual master with 8" dual booster. Are the 10psi valves needed to "take up slack" or "to keep the wheel cylinder cups inflated"?

Correct. Without the valve (or cup expanders), you will have a soft brake pedal as on brake release, the wheel cylinder cups will flutter causing either air ingestion and/or fluid leakage. Over time the pedal will get soft and the pedal height will be low. Low pedal can also be as a result of the rear drums not being adjusted correctly also).

I was a mechanic for 10 years and all we ever worried about was proportioning valves!

Supposedly residual pressure valves are built into factor proportioning valves?

Also, I assume for a drum/drum car no proportioning valve is needed.... there certainly wasn't one from the factory, but we are now over 60 years later and I'd like itsing brake shoe size to be better than factory.

GM did use a PPV (pro-portioning valve) on some drum/drum applications. It all depends on brake design/bias. A car brake system is designed to perform correctly as assembled with specific MC bore size, brake tubing size, wheel cylinder size and brake shoe size. When you begin to modify is where you will encounter problems.

You have a 59 FORD with all OEM braking except for an aftermarket MC?

[KULTULZ]

In MC RESIDUAL VALVES shown in DUAL RESERVOIR MC (DRUM-DRUM) and FREE-STANDING -

A DISC-DRUM MC will have the valve only in the SECONDARY OUTLET (Drum Brake Outlet).

[59meteor]

Although the OE manufacturers may have had things like RPVs, or springs inside the wheel cylinders, I have to wonder if all of the cheap offshore parts flooding the market have 100% OE specs and features. You would think that they SHOULD, but.....

[KULTULZ]

Although the OE manufacturers may have had things like RPVs, or springs inside the wheel cylinders, I have to wonder if all of the cheap offshore parts flooding the market have 100% OE specs and features. You would think that they SHOULD, but.....

EXACTLY and GOOD POST.

I just recently went through my ESCAPE with CENTRIC brake parts and was amazed at the quality. It was better than MOTORCRAFT.

With all of this CHINA one-offs one has to be very careful. Even some of these kit vendors are using it.