Thread: Residual Pressure Valve

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Ok I'm starting on the brake system on my 40 ford p/u and would like to know is it wise or necessary to use residual pressure valves ? I do have and plan on installing a adjustable proportioning valve. This is with power brakes, disc on front and drums on the rear.
Also is it best to do the inverted double Flare on the lines ?
Thanks again for the inputs !

floor or firewall ?

Originally Posted by shine

floor or firewall ?

Master cyl. in mounted in the frame along with the brake pedal assy. I don't see what difference that would make. Please educate me. Thanks.

When running a disc/drum setup, you want to use a 2lb residual valve for the front and a 10lb for the rear. You also want to run them inline as close to the MC as you can. The proportioning valve should be on the frame at the back so it's accessible from underneath to adjust.
The residual valves keeps brake fluid from draining back to the MC. That way the pedal does not get mushy. The proportioning valve will help you regulate pressure from front the rear.

Correct me if I'm wrong - you don't need it for firewall mount

Originally Posted by firebird77clone

Correct me if I'm wrong - you don't need it for firewall mount

As a general rule, but drum brakes might be helped by one. The return springs on drums can force the shoes back away from the drums. This can cause additional pumping to get the shoes out where they need to be. Doesn't always happen, but it can. Disc/drum master cylinders usually come with residual valves in the rear circuit under the brass seat in the rear fitting. Disc brakes don't have return springs so it's not an issue.

As to the OP question about double flares. Yes, never use single flares on brake lines, unless you're using the 37* AN fittings. The double flare is intended to reinforce the flare, the AN fitting uses a machined sleeve to do this.

I have a firewall mounted MC with 4 wheel disc brakes. I have two inline 2lb residual valves that are inline and close to the MC. You need two 2 lb for 4 wheel discs. And my adjustable proportioning valve is on the side of the frame near the front of the rear tire.
You can get away with not running the residual valves, but when you hit the pedal the first time it will be soft. Then when youhit it agian it will get alittle harder. The valves keeps fluid from draining back.

If the Master is firewall mounted, (above the brake cylinders / calipers) then gravity will force the fluid to remain in them (cylinders/calipers)

If the master is under the floor then the fluid has a chance to actually flow back to the master and this will cause a low pedal and that first press on the pedal will be needed to refill the cylinders/calipers.

The residual valves hold the fluid back keeping the fluid where it's needed.

Seems to me, if the drum springs pull the shoes far enough to cause excessive pedal movement, then the self adjusters have an issue.

There is a second reason for having residual valves on drum brakes. The small amount of residual pressure keeps the cups in the wheel cylinders expanded. This prevents air from being drawn into the system. Some later drums have expanders on the internal wheel cylinder springs that eliminate this problem.

Here are some links:

Typical Brake System Configurations

Camaro Brake Valves

Classic Chevy, Chevrolet, GMC, Ford technical articles

Hot Rodder's Bible : The Ultimate Guide to Building Your Dream Machine - Steve Hendrickson Gerry Burger - Google Books

Brake Systems: OEM & Racing Brake Technology - Mike Mavrigian, Larry W. Carley - Google Books

Designing Your Brake System