New to Mix-and-Match Brake Systems

[steve aleve]

I am new to creating my own mix-n-match brake system and I wanted to see if I could get help from the pro's out there. I am actually pretty new to brakes in general!!! I have an AD that is going on an S10 frame. I have the stock s10 disc setup up front, a s10 blazer rear axle with discs, and a hydroboost from a mid 90's astro. I have the hydroboost hooked up and most of the lines that run along the s10 frame are there. I just need to connect the 3 lines (rear axle line, DS front line and PS front line) to the hydroboost. My question is mainly in regards to compatibility and selection of a proportioning valve. Does it make the most sense to use the proportioning valve off of the blazer so that the 4W disc setup is fed the same as it was originally intended? Hope this makes sense.

s10 discs up front
blazer discs in rear
astro hydroboost with stock MC etc.
______ proportioning valve

Thanks!

[PurdueSD]

I hear ya, I'm looking forward to seeing some answers/advice here!

[HUSSEY]

I can tell you what I'm doing based on my research. I'm running front an rear disks. The front and rear setups are out of a 2000 Blazer. Front has the twin piston calipers. My master cylinder is out of a 1980 Corvette which has Disk/Disks.

I'm not installing a proportioning valve for now. Once I get it out I'll test it out and if the rears lock up under heavy breaking then I'll add a simple in-line proportioning valve to the rear disks.

If you want to add a proportioning valve, I would go with one from Wilwood that goes in-line and is adjustable. A fixed valve wouldn't do you much good unless it just happens to work just right.

http://www.jegs.com/i/Wilwood/950/26...FYIBaQod0AoIXA

[HUSSEY]

I read a really good article and I wanted to a paste a link to it but I can't find it so I'll just paste it below.

The pictures are the best I have but you can zoom in on them.

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Editors Note: Innovative Brake Technology by The Brake Man, Inc., has a long and distinguished history of developing leading edge technology for the automotive and racing industry. Warren Gilliland, the President and CEO, has been designing advanced brake systems since 1967, far longer than any other American aftermarket company. Mr. Gilliland's focus and commitment to technological leadership have formed the core competencies at The Brake Man, Inc. From the early days At Hurst/Airheart in the late 60's, and throughout the 80's at JFZ Engineered Products, the key technologies that are foundational to The Brake Man, Inc. have been the source of setting the trends for advancement of the industry. The Brake Man is among the most knowledgeable sources of information for improving brake systems, while supplying high quality brake components, and most importantly, a reliable source of information on how to make the system produce the best results.

UNDERSTANDING THE VALVES OF THE BRAKE SYSTEM, PART I

A few weeks ago, a friend of mine called from back east to ask about a problem he was having with the brakes on his recently purchased 40 Ford Street Rod. The front disc brakes were dragging and wearing out quickly. The stock master cylinder was also leaking. Since I have a variety of repair parts at my disposal, I had him take it off the car and send the master to me.
Just as I suspected, I found the source of his front brake drag still in place inside the master cylinder. The residual valve. This little misunderstood valve can create havoc in a brake system both when used improperly, and when it is absent.
Very simply, the residual valve found in the drum brake systems is not compatible with the disc brake conversions you install to update a vehicle?s brake system. This valve, as with all valves of the brake system, have very specific guidelines governing their usage. The purpose of this article is to explain each valve and it's proper usage. Everyone with a modified brake system should check their system valves to be sure they meet the guidelines discussed here. If they do not, corrections should be made immediately.

The street rod mentioned here has very little, if anything in common with the kind of cars most of you reading this article drive, but the idea is the same. You can?t just make changes to your brake system without putting in some thought as to making sure the system will work when you are done.

Whether you drive a Honda Civic, Acura Integra, Nissan Ultima, or any other kind of car, the brake system consists of much more than just the brakes on the wheels. The system valves are meant to control how the front and rear brakes work together to give you a safe vehicle under all stopping conditions.

The whole purpose of installing any valve in a brake system is for one simple purpose. That is, to make the braking power being generated from the front and rear systems, consistent with each other throughout the pressure ranges encountered under all stopping conditions. If you graphed the brake torque from the front and rear brakes and they were in the proper distribution under all varying line pressures, there would be no need to install any additional valves. Take a look at the graphs included in this article and see how disc and drum brakes differ in their torque output, and how torque generated from each becomes unbalanced at certain extremes.
We may as well start with the residual valve, because it is the first one that should be determined whether or not it is needed. This valve does exactly as its name suggests. It keeps a pre-determined amount of residual pressure in the line after you remove your foot from the brake pedal. This aids in preventing excessive pedal travel as well as insuring consistent height to the pedal. In a drum brake, heavy return springs are present to pull the shoes away from the drums. When not in use, the shoes are pulled back until they rest on a centering pin, usually located at the 12:00, or top position, on the backing plate also holding the wheel cylinder. In order to avoid the excessive pedal travel to move enough fluid from the master to activate the shoes, a 10-12 pound residual valve is installed in the line. Sine the return springs are stronger than the 12 pound valve, the shoes are pulled away from the drum in spite of the resistance so no brake drag results.
A disc brake system, however, cannot tolerate this kind of pressure, as it would cause the pad to rub the rotor even when your foot was off the brake pedal. 10-12 pounds of line pressure on a disc brake will cause detrimental drag and a tremendous decrease in pad life. Worse yet, if the vehicle is driven at a consistent speed, the temperature will climb, due to this drag. This will cause the pads, rotors and brake fluid to swell causing lockup. At that point, the only way the brake system will release is for everything to cool back down.

In a stock system, the master cylinder is mounted high on the firewall. The gravity of the fluid in the master will cause 1-2 pounds of natural residual pressure, which is sufficient to maintain constant pedal height in a disc brake. It is for this reason, in most cases, a residual valve is not used with a disc brake. There is one very notable exception. This is when the master cylinder is installed lower than the caliper or drum wheel cylinder. In this case, the fluid would want to return to the master cylinder by flowing downhill like a river. The result would be a low pedal or even no pedal at all! To stop fluid rollback, we would want a 2 pound residual valve, which is just sufficient to stop rollback, but not enough to cause harmful brake application.
If you are running disc brakes with a master cylinder mounted below the floorboard without a residual valve, such as you might see on a highly customized car that would be trying to hide the ugly master on the firewall, excessive pedal travel and brake loss could result. Correct this condition immediately, even if you have not had a problem yet.
To really get the most practical benefit from this information, you first need to know what valves are in your system, and where they are located. The residual valve, for example, could be found in a variety of locations. On most American cars and trucks up to the mid 1960's, the valve will probably be found inside the master cylinder. In a single master cylinder, it will be located at the bottom of the bore and look like a little brimmed hat. In a tandem master, it will be in one or both outlet ports and look like a brass seat. On most all American and foreign newer cars, the residual valve is usually incorporated with other valves in a "combination" valve. (More about the other valves later). This combination valve can be located on a stock vehicle by simply following the line out of the master cylinder until you arrive at a junction block. This block usually has two lines going in from the master and two lines going out, one to the front brakes and one to the rear brakes. Most commonly, the combination valve is found on the firewall, within a foot of the master, just beneath the master, or on the left frame rail near the lower "A" arm.
If you have removed the combination valve, usually found under the master cylinder, then you have removed all of the valves on your system. It is important that you contact someone knowledgeable on your vehicle to put it back to a safe condition, and read the rest of this article to find out the problems you have created.

It is also possible that a line valve may have been installed pretty much anywhere in the lines to either the front or rear, or both. Since the valve is only slightly larger than a standard connector fitting, use care in looking for this valve. After market valves can be installed backwards, even though most valves are clearly marked with some kind of an indication as to which end of the valve should point to the master or the brakes. If a valve is installed backwards, it is like not having one installed at all. Be sure a line valve is installed correctly.

If you purchased the vehicle and the system was installed by the previous owner, make sure you check it. You must now be sure it is working. Since a residual valve may incorporate a diaphragm, the use of a sharp object such as a pin could puncture the diaphragm make the valve useless. In the case of the brake seat type in the outlet port of a tandem master cylinder, it may have been removed entirely, as they are only pressed in.
There is a simple though not foolproof method of checking to see if your system has residual pressure. With the brake system at rest, open a bleed screw on a wheel cylinder or caliper. If even a few drops of fluid come out, residual pressure is probably present. If the wheels are off the ground on a disc brake car, depress the brake pedal firmly and lift off. Attempt to turn the wheel just slightly to feel the amount of drag. Open the caliper bleed screw and close. If the wheel now turns more freely, residual pressure is probably present.

Occasionally, another problem in the brake system will be mistaken for a residual valve. This is when the master cylinder pushrod length has been improperly adjusted in such a way, as to not allow the piston to return all the way to the back of the bore. If the piston does not return all the way, the cup in front of the piston will not move back far enough to open the bleed hole. When the bleed hole is not open, residual line pressure is the result. Unfortunately, this type of residual pressure is not controllable and gets worse the harder the brakes are applied. Master cylinder pushrods always should have "free play" to insure that the piston can return all the way back when pressure is released.
As you can see, there is more information about valves than we can cover in one article. So, in order to do a thorough job, we will complete this article next issue. Between now and then, if this article made you squirm and you identify with any of the conditions we discussed, check your system and find out how your system is plumbed immediately. If your car has a pedal that goes close to the floor after sitting for some time, and then is fine after the first application, you definitely have some of the problems we discussed. If your pedal height never seems to be quite the same, or if it is always low and spongy, you need to correct it. I've driven a car that had the pedal go to the floor. Believe me, it is a feeling that you never want to experience yourself. I was lucky. I'm still here to help you fix yours.

Brake Valves, Part II

The tech line at "The Brake Man" gives us a great opportunity to find out many of the misconceptions that exist in the real world. It seems ironic that in both the oval track racing industry, and the street performance industry, a new disease among the owners and drivers has sprung up. This disease is called "proportioningvalveitis", (owners overwhelming desire to install a proportioning valve for no particular reason, other than he thought he ought to have one because he thought everyone else did). The only characteristic of this disease is that a valve is purchased and installed without bothering to find out if it is needed. In street performance cars, where consistent braking is often the key to a fast performance car, they are NEVER a good idea, because there are better, more consistent ways to modify brake pressure on a car. For example, on most vehicles I checked, about 4 out of 5 now in use are causing more problems and system imbalance than they fixed.
The proportioning valve is the most often misused valve in the brake system. The most important thing to understand about the proportioning valve, is that is was never intended to be used in every brake system, in fact, NO VALVE WAS MEANT TO BE IN EVERY BRAKE SYSTEM. Just like a hammer in your tool chest, you only should use it when you need it. In fact, the chances are far greater that you don't need one, than you do. As with all valves of the brake system, the proportioning valve performs one function for one specific situation, and that's all. You must first see if your system has a problem that a proportioning valve will correct. That problem is imbalance, and even then, the proportioning valve is only one way to fix it. The best way to understand what a proportioning valve does is to look at a graph of pressure output of a brake system over the entire pressure range. Please note the graph in figure one shows a disc front, drum rear combination. This is really the only combination that can best benefit from a proportioning valve, and even then, only if certain conditions exist.

As you can see, in a system without valves on a stock vehicle, the front brake torque is simply represented by a straight line. This straight line represents the increase in torque that is produced by a disc brake. That is to say, pressure in is a linear function when compared to torque output. The curve representing torque from a self-energizing drum brake is represented by the curved line, which indicates two interesting characteristics of a drum brake. First, you can see that the disc brake started creating brake torque as soon as applied. In comparison, however, the drum brake does not begin to produce torque until the system pressure is over 100 pounds. Why? Because the rear drums have strong return springs to hold the shoes away from contact with the drum. Until the line pressure overcomes the spring tension, the shoes will not even move into contact with the drum. Once that does happen, the torque rises dramatically, even faster than the input of line pressure. This is because, on a drum brake, there is a characteristic known as self-energizing, which means the shoe is actually pulled into the drum surface. This causes the pressure to rise much faster than the increase in the disc brake torque and the lines actually cross at about 1000 pounds per square inch.

A stock vehicle, in most cases has more of the weight on the front wheels. When you combine this with the fact that there is an approximate weight shift of another 10% of the vehicle weight to the front during braking, you can see the rear brake will lock up first if this condition is not corrected. When the rear brakes lock up on a vehicle, the rear wheels are now traveling faster than the front wheels, which are still in full contact with the road. The result is a car that has the back end pass the front end, better known as "spinning out".

Now before you panic and go buy a proportioning valve for your car, you need to know one additional piece of information. You may not need it. Why? Because the height, (not the width), of the tire on the back of the car must be compared to the front tires first. Take a measurement from the center of the tire, (where the spindle is located), to the ground, both front and rear. This will tell you the "rolling radius" of the wheel. If the rear is greater than the front, then you will need to leave the line pressure higher on the rear because, the larger the tire, the more brake required to stop it from turning. If the tire on the rear is substantially larger than the tire on the front, then major increases in rear brake pressure are required.
When a vehicle is built at the factory, the brake system is balanced by the size of the caliper and rotors chosen for both the front and rear. Unless you are removing rear drum brakes and upgrading to disc brakes, the valves will most likely not require changing. However, if you do remove drum rears in favor of discs, take note of two important items.
You must locate and remove the 10 pound residual valve. It will ruin the rear disc brakes. Make sure you do not improve rear brake performance when making this change, because if you install better rear brakes, the front brakes must be improved too.
If you study the graph in figure 1(below) closely, it will alert you to another important and potentially damaging problem. Under low pressure stops, (those normally encountered under 30 mph, cruising situations), the front brakes are doing all the work in stopping the car because the rear drum brakes have not yet received sufficient pressure to overcome the return springs. This will result in extremely premature front pad wear. In a stock passenger car, imbalance is corrected by a metering valve. The metering valve stops the first 100 pounds of pressure from reaching the front brakes thus allowing the rear brakes to overcome the return springs and apply at approximately the same time as the front. This is the valve that is truly needed to balance the system.

Figure 2 illustrates how torque output from the front and rear brakes compare when a metering valve and proportioning valve are installed on a stock system. Don't forget that large tires on the rear would require more, and that the proportioning valve would be robbing the vehicle of available brake it really needs.
A proportioning valve NEVER gives you more brake, it only takes away available brake effort. You should be sure that your situation benefits from a less brake condition.
Since many of the most important factors in balancing the brake system are never the same from one vehicle to the next, (weight ratio, tire size etc), the only proper way to determine whether you have developed a well balanced system is to first plan what you need. Then, based on your system components, test it when you feel you have it correct. Take the car to an isolated location so you can perform several hard decelerations. Start at low speeds, 20 mph, and perform a fast stop, similar to one you may do if a light turned red and you were very close to the intersection. Then try the same stop at 30 mph, then 40 mph, allowing the brakes to cool for 5-7 minutes in between. Continue this up to 60 mph, or any speed you expect to encounter during the vehicle's actual usage. If at any time you encounter premature rear wheel lockup, or front wheel lockup, then the system is not yet properly balanced. If the rear wheels lock up, then you will need a proportioning valve to reduce rear pressure. Most of you will find this is not the case and no proportioning valve will be needed. The biggest problem I am seeing right now in getting safe brake systems on any vehicle, is the approach of the car owner. It is not enough just to get the car to stop. It must be balanced throughout the range of speeds and pressures. There is also a misconception that taking a complete system off a stock car will give the owner everything they need to set up a safe system on their vehicle. Nothing could be further from the truth. Unless your car has exactly the same weight ratio, tire size, wheel base, center of gravity, etc. etc. the system will have to be modified, maybe excessively, to work on the new machine.
In stock production cars, the proportioning valve and metering valve are usually combined into what is referred to as a combination valve. Different manufacturers combine different valves into the combination valve. In some cases they're combined with a failure warning light switch. In other cases, they are combined with the residual valve. The two most normal stock locations for finding these valves are: 1) on the firewall towards the center of the car from the master cylinder, 2) On the left frame rail usually about even with the front tire.

In both cases the valves can be located by tracing the brake lines from the master cylinder. These valves should not be used unless you are positive that all system components in that combination valve fit your needs, exactly.
Figure 3 and Figure 4 have been included to show you the relative torque outputs of an all disc system and an all drum system. As you can see, since in both cases, the lines already follow each other closely, a proportioning valve would do more harm than good.

There is an old saying, "when you are up to your butt in alligators, it is difficult to remind yourself that your initial objective was to drain the swamp". If you apply that logic to your brake system, remember that your objective is to balance the brake torque to each wheel, based on the weight on that wheel during deceleration. In other words, you want each wheel to do its proportionate share of stopping the vehicle without locking up prematurely. If you don't have the ability to consider these factors, then get someone knowledgeable to help.

I think we all share the concern of wanting our car to stop safely, especially our own and those immediately behind us. If you have built a project car, and are proud as can be of how it looks and runs, add one requirement to your goals. Make sure it will stop under any, and all conditions. Sometimes it only means a little more work and attention to detail to make that happen. The proper combination of valves will make this happen. Do not install parts you are not sure you need. When an owner calls and asks my advice on which components to use, I must look at that car and its individual merits before answering. In order to achieve the best results, you must do the same. A doctor must treat their individual patient's particular needs. If you attempt to grab a generic remedy, you will probably not be happy with the results. Your car is most likely one of a kind. The brake system must fit its needs.
Editor's Note: The modified brake system constitutes one of the most misunderstood portions of the car. Because of this, there are many unsafe cars on the road. Please understand that this article is for information only, and there is no responsibility of the magazine or of Gilliland/The Brake Man for reader use of the information. We are attempting to inform the reader of concerns they should have for their safety. In vehicle braking, as with everything to do with performance automotive, and racing, there will be a wide variety of factors affecting outcome. This article was intended to help you see how these factors can affect your finished product. If you would like to learn more, contact this magazine.




FIG. 1. THIS GRAPH ILLUSTRATES WHAT KIND OF TORQUE OUTPUT WOULD BE CREATED BY A TANDEM MASTER CYLINDER PRODUCING THE SAME PRESSURE TO A FRONT DISC, REAR DRUM TYPICAL BRAKE SYSTEM WITHOUT ANY TYPES OF VALVES PRESENT. AS YOU CAN SEE, THE DISC BRAKE FRONT WOULD IMMEDIATELY BEGIN TO GENERATE TORQUE, WHILE THE REAR DRUMS WOULD BE CONSISTENTLY LOWER UNTIL THE PRESSURE REACHES ABOUT 1000 POUNDS LINE PRESSURE. AT THAT POINT, IT WOULD ACTUALLY BE PRODUCING MORE TORQUE THAN THE FRONT BRAKES. SINCE 1000 POUNDS LINE PRESSURE IS ONLY SEEN IN SEVERE PANIC STOPS, THIS WOULD RESULT IN REAR WHEEL BRAKE LOCKUP SINCE THE WEIGHT HAS SHIFTED TO THE FRONT WHEELS. THIS IS CLEARLY AN UNSAFE SYSTEM!



FIG. 2 THIS GRAPH ILLUSTRATES THE SAME CONDITIONS AS FIGURE ONE, ONLY NOW WE HAVE ADDED A METERING VALVE AND PROPORTIONING VALVE. AS YOU CAN SEE, THE METERING VALVE DELAYED THE FRONT BRAKES UNTIL THE REARS HAD A CHANCE TO JOIN IN THE JOB AT ABOUT THE SAME TIME. ALSO, SINCE A PROPORTIONING VALVE HAS REDUCED THE AMOUNT OF PRESSURE THAT THE REAR BRAKES RECEIVE, THE TORQUE OUTPUT HAS RISEN MUCH MORE GRADUALLY, REMAINING LOWER THAN THE FRONT THROUGHOUT THE CRUCIAL RANGE.



FIG. 3 THIS GRAPH COMPARES AN IDEALLY BALANCED BRAKE SYSTEM THAT HAS 4 WHEEL DISC BRAKES. A METERING VALVE IS NOT NEEDED TO STOP PRESSURE TO THE FRONTS, SO IT IS NOT PRESENT. THE RESULT IS A BRAKE SYSTEM THAN BEGINS TOGETHER AND CLIMBS APPROPRIATELY. THE REAR DISC BRAKES HAVE SMALLER PISTONS, WHICH RESULTS IN A LINEAR REDUCTION IN BRAKE TORQUE. THIS IS EXCELLENT, BECAUSE AS THE STOP BECOMES MORE SEVERE, PRODUCING HIGHER LINE PRESSURES ALSO MEANS THAT THE WEIGHT ON THE REAR IS SHIFTING TO THE FRONT. AS THE REAR GETS LIGHTER, LESS BRAKING FORCE IS REQUIRED TO STOP THE WHEEL FROM TURNING. SINCE THE SMALLER PISTONS ON THE REAR CALIPERS PRODUCE LESS TORQUE, NO PROPORTIONING VALVE IS NEEDED FOR BALANCE.



FIG. 4. FIGURE 4 ILLUSTRATES A FOUR WHEEL DRUM BRAKE VEHICLE PROPERLY BALANCED. SINCE BOTH THE FRONT AND REAR WHEELS HAVE RETURN SPRINGS, NO METERING VALVE IS REQUIRED TO DELAY EITHER END. ALSO, SINCE BOTH HAVE A SELF ENERGIZING DRUM BRAKE CHARACTERISTIC INCREASE IN TORQUE, ONLY A SMALLER WHEEL CYLINDER IS NEEDED ON THE REAR TO PROPERLY BALANCE THE SYSTEM. HENCE, NO PROPORTIONING VALVE IS NEED HERE EITHER.

[steve aleve]

PurdueSD, thanks for the support! Glad I am not alone in this one and thanks HUSSEY!!!! That is killer info and I think I will plan on going a similar route as you. Probably get things running and install an adjustable in line valve to control it.

[OrrieG]

If you lowered the truck and the MC is down on the frame you might need residual check valves it the MC does not have them.

[tmoble]

if you're running the S-10 brakes front and rear just use the S-10 master and valve. The hydra-boost is a power assist unit like a the big diaphragm style, don't really impact the hydraulics.

There's no good reason to open a can of worms with adding un-needed aftermarket stuff into a good system. My 2001 4WD Blazer has truly excellent brakes, hard to improve on. Of course, no vendor selling brake parts is going to admit that.

[HUSSEY]

Originally Posted by tmoble

if you're running the S-10 brakes front and rear just use the S-10 master and valve. The hydra-boost is a power assist unit like a the big diaphragm style, don't really impact the hydraulics.

There's no good reason to open a can of worms with adding un-needed aftermarket stuff into a good system. My 2001 4WD Blazer has truly excellent brakes, hard to improve on. Of course, no vendor selling brake parts is going to admit that.

I don't think a 2001 Blazer has a standalone proportioning valve. Check under the hood, I could be wrong, but would like to know.

[PurdueSD]

So lets just say (for arguments sake of course) ...you aren't running s10 brakes front and rear. -Your system is a little more mix and match like say: you have granada 11" discs up front on your ifs, 99 explorer rear axle discs and 87 suburban vacuum booster.

My suburban master is disc/ drum and had a proportioning valve/ metering block in the suburban. I was planning on using the disc drum master and running a inline adjustable proportioning valve for the rear would this be a good starting point. What about line sizes front and rear? Thanks fellas!

[HUSSEY]

^^^^^
For GM the master cylinder uses a 3/16 in. line and 1/2-20 nut for the front and a 1/4 in. line and 9/16-18 nut. I don't now what size the Ford lines are but you can use adapters or change out the tube nut at the end.

I just finished plumbing up my brakes and bought all my lines and fittings at Advance Auto.

The master cylinder is a harder question to answer. I would make sure there is no residual valve for the rear drum brakes in the your master cylinder. I've been told that after a certain year GM quit installing them but I don't know what year that was. From there, trying to match up the master cylinder bore to your system may be a bit experimental.

[dwcsr]

We used a 11" universal booster, MC2912H 1-1/8" corvette style master, PV4K-2 Disc/Disc prop valve 3/16" lines. You can substitute a Hydro-Boost for the 11" Booster. This truck stops very well, no rear wheel lockup.

[PurdueSD]

Thanks @Hussy and @dwcsr !!