The Stovebolt Site Forums The Shop Area The HiPo Shop Proportioning valve/Residual valve position Ques.

I am installing a 7/8" bore master cylinder with a 2 stage (pancake type) booster. The sysyem will include a proportioning valve with 2 lb. (front) and 10 lb. (rear) residual valves. Front brakes are 11 inch '85-'87 Corvette disc and rear brakes are '86 Camero drum. Ques....Can the residual valves be mounted between the master cylinder and porortioning valve or must the residual valvs always be mounted between the porortioning valve and brakes? Thanks in advance.

In most factory applications the residual valves are a component in the master cylinder. Likely the residual valves would be as close to the master as practical. If you purchased an aftermarket kit the lines from the master to the proportioning valve are already formed and everything fits nicely with the mount bracket. In that instance it might be better to locate the residual valves in the lines aft of the prop valve. I have seen them both ways and have not heard of any problems. Many of the aftermarket suppliers build the residual valves into the system specific to your application therefore separate valves are not necessary.
Fred

Thanks for the quick response. The master cylinder is a 1980 Mercury Cougar. I checked and it does not have the valves in the outlet ports. The system was purchased in pieces at several car shows.

I have to question the 7/8 bore. Most manual brake systems use a 1 inch bore, and most power systems use a larger bore... 1 1/16 or 1 1/8. I am concearned you might have too much pedal travel.

I know how tight money can be, but brakes are the most important system on any vehicle. The after market MC kits are a much safer option than a system cobbled together from finds at several car shows.

I've used residual valves between the MC and proportioning valve, that's where I think they are supposed to go.

But the real question (in my mind) is did the original brake system have a residual valve? And if not then why do we need them now?
I used them because I was told I had to, but I have yet to hear a really good reason and explanation. The MC is higher than the wheel cylinders although it is not by much.

Grigg

A residual valve was included in the M/C on all-drum systems way back when, to keep the brake lines full and prevent air from being pulled past the wheel cylinder cups when the pressure at the brake pedal went away. The brake shoe return springs were sufficient to overcome the residual pressure and allow the shoes to move away from the drums and prevent drag. Since disc brake caliper pistons have no return springs, little or no residual pressure can be allowed against the calipers. Disc pads are intended to have a slight drag on the rotors in most systems to act as a squeege after a disc is exposed to splashed water. It's also intended to prevent excessive pedal travel and to compensate for pad wear by allowing the pistons to follow the pads as they wear. Most caliper seals are square-cut, which provides a slight retraction of the pistons to prevent excessive drag as the pressure on the brake pedal is released.
Jerry

Question... with residual valves on rear drum brakes doesn't it keep a few pounds of pressure on the wheel cylinders/shoes and that gives you a "quicker" and a firmer peddle when you do apply the brakes. Right? Just curious about this.

Achipmunk...that's their stated purpose. Ten pounds for drums (return springs like "Hotrod" said, and 2 pounds for disc. I checked for residuals in the M/C body using a wood dowel (actually a wooden Q-tip). Carefully insert in the outlet ports. If it just goes a short distance(say 3/16" or less) then there are valves in the body. If it goes in 1/4" or greater, then no.
As to other questions... The 7/8" bore is due to the smaller than I would like booster (under floor setup with limited space). Residuals valves because my M/C is level/lower than the slave cylinders. And lastly, I called a supplier of performance brake part/systems to the hotrod world. They stated residuals always go after the proportioning valve. I didn't ask why.

If this is true, then on proportioning valves with the built in distribution block (normal GM type) allowing separate lines for the front brakes do they recommend you use two separate residual valves for the front brake lines?

I've installed my residual valves between MC and proportioning valve, when I researched it that is how I thought it was supposed to be, can't remember exactly why now, but it does make sense I think.

Here's some info
http://www.ecihotrodbrakes.com/brake_facts.html
They don't explain location, but in the pictures they show with adjustable proportioning valves the residuals go between the MC and the valve.

Any other thoughts or reasons on where and why?

Grigg

Grigg, I'm going to call several other suppliers like M&P Brakes and ask why this time. I'll have to buy another 2 pound residual if true. I let you know what they say. Darn it, I know it's only money, BUT it's My money!

OK, it just came to me... consider this situation:
Many stock MC's have a residual valve or two in the MC, these are quite obviously before the proportioning valve.

Now I see no reason that the residual needs to be or should be after the proportioning valve.

We may find it works either place, I'm not sure, but duplicating a factory system is likely the right answer, so it goes between MC and proportioning valve.
Unless you've seen a factory system with them after the proportioning valve??

Grigg

I have asked these same questions many time and conducted an exhaustive amount of research and I believe my system to be correct as it is currently plumbed. In researching I did find some sites that showed the plumbing different, but the configuration I used is the one most generally used.

Here is a picture of my MC plumbing. The front residual valve is behind the MC, so it is not visible in this picture. MC Plumbing

...IF I can find it I have a full page diagram of where they go for drum/disc or drum/drum...... it came with the M/C, booster,pedal and brackets, along with the residual valves. It has some interesteing reading. I know you guys can find plenty to read without it so I won't look to hard right now...but will when I put them on!!

Alvin, here's what I found at the Master Power brakes site.
M/C and brake plumbing

In short it shows the residual valves after the proportioning valve.
Now that we have trusted sources (factory applications and MP brakes) showing both ways I wonder what the reasoning is for each, or does it even matter?

Grigg

Grigg, AFAIK the residual valves are there purely to stop fluid drain back due to the M/C being lower than the calipers/brake cylinders on under floor applications,so would a firewall M/C even need them??
Whereas the proportioning valve is to provide balance between front and rears.

I've been led to believe the residual valves should be placed as close to their respective ends as possible.
I wonder if there's any definitive answers out there?

It's getting to the point who do we believe? I don't know.....
Someone out there must know.

Even with the MC higher than the wheel cylinders supposedly residual valves provide for a firmer pedal feel on drum brakes, or rear drums if you have front disc. Because the brake shoe return springs have a lot more force than the wheel cylinder at 10 psi they do retract and don't drag, so no harm that I can see.

I think some proportioning valves "combination valves" have the 10 lb residual built in for rear drums..

Thinking about how they work I really am beginning to wonder if it makes any difference where they go, but like you, suspect that closest to the MC is still best.

Grigg

Jock, that is basically what I remember having. Now that my memory has been jogged the sheet I have also list the residuals AFTER the master cylinder. All in all I think it depends on what kind of m/c you use?? There I go "thinking" again. That usually gets me in trouble!!

Wow!!! I had no idea that the position of the residual valves would bring up so much discussion. I called "MP Brakes" over in North Carolina. They said that "anywhere down stream of the M/C is OK". To be more specific, I asked. "So, one can put the residuals valves either before or after the protortioning valve, correct"? Their answer was, "yes". I believe Grigg has it right. My old M/C setup has the residual valves before the proportioning valve and I'm going to keep it that way with the new one. It will save me time and effort re-plumbing. Thanks

Glad you got it cleared up beltfed......

I think much of the confusion is coming from the lack of distinction between "distribution blocks", "proportion valves" and "combination valves".

THEY ARE NOT THE SAME THING.

A "combination valve" is usually a distribution block that includes a "proportion valve" and sometimes a "residual valve". The "combination valve" also includes a "brake light switch" and a "metering valve".
If you have drum/drum after about 1967 with dual MC it will have a "distribution block" with a "brake light switch" and NOTHING else inside of it. It separates the front and back system and turns the brake light ON if either fails. Nothing else.

A combination valve does a pressure dance as the pressure rises from 0 psi up to 1000-1500 psi. The "metering valve" restricts pressure to the front disc until the rear sees 50 psi. From 50 psi up to about 200 psi the front and rear see the same pressure. After 200 psi the 'proportion valve" reduces the rear pressure below the front pressure. The higher the total pressure, the greater the difference between front and rear.

A "proportion valve" doesn't care about the "residual valve's" 10 psi, because it operates above 200 psi. The "metering valve" operates from 0 psi to 50 psi, so the 10 psi "residual valve" can upset the way the "metering valve" was intended to operate on the car THAT "combination valve" was intended to be installed into. I've always understood the "residual valve" should be in the "combo valve or after a stand-alone "metering valve" if that is used and one is needed on the front side.
The 50 psi and 200 psi numbers I used are different for every car/truck.

Aftermarket "proportion valves" are adjustable. Many of the aftermarket brake guys also sell separate "metering valves".
The purpose of the "metering valve" is to push the rear shoes against the drum to create some rear drag, before the front brakes begin to work. That is done for stability and to prevent nose dive on your street car/truck. Race cars have stiff suspensions and usually don't need them.