Technical Some brake questions !!!

I think what tends to happen is people use a proportioning valve to try to make mismatched components work instead of to balance vehicle dynamics, such as a pickup etc.


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that was what I was thinking also, guys have a problem and they throw another part into the equation. if it works a little, it becomes the "cure-all".

 

It's very difficult to have a balanced disc/drum system without proportioning simply because of the higher pressure requirements of discs vs drums. If you reduce the drum effectiveness too much, you overwork the front discs, along with not having enough rear brake for parking and rear-only (vertical split) stopping in the event of a partial system failure. Pickup trucks are prime examples of needed proportioning because of the very large weight bias changes from GVW to light load..
When front drive cars came along, the large front weight bias required more work of the front brakes and less from the rears, but parking and partial systems DOT requirements brought about the cross-split hydraulic systems with one front and one rear on one circuit. Now very small rear drum brakes could be used for better brake balance, and DOT requirements were met, but proportioning was still used!

 

I fully agree with you Bob, I was getting at the fact some people think they can throw any parts together and add a proportioning valve and have a perfectly functioning system. As seen by this thread, a lot of planning should go into a brake system.

 

This is going to sound crazy so bear with me......
Consider the brake fluid a solid. There's no real "flow" as this material acts as a "solid" in a closed system. Fluid is not compressible, air on the other hand is.
Since fluid is not compressible and this is a closed system, the volume of fluid pushed out of the master pushes all the brake system's pistons.

In the simplest example, the fluid is a solid link from the brake pedal to the brake cylinder or caliper pistons.
The brake lines could be 3/16.. 1/4....3/4.....even a absurd 2". If this closed system with 2" lines was purged of all compressible air, the function would be the same as if it was 3/16.

Being a fluid it can be contained in piping. This means it can be routed nearly anywhere. On the other hand, a system of rods and solid linkage cannot.
The compact hydro system is efficient in it's use of mechanical advantage as well.

 

F-ONE.......I understand your point but fail to understand why you quoted my post since your comments do not refute anything I wrote.

Yes, liquids generally are considered non-compressible and in that particular respect, they have some characteristics of ‘solids’. But liquids are not truly solids unless they are at or below there freezing point.

My comments solely addressed flow of a pressurized liquid threw a reduced orifice while at a constant pressure. The speed (velocity) of the liquid would accelerate at the restricted orifice. The fact that not much volume is moving in the average brake system when brakes are applied is not the point....the effect is the same nonetheless.

That physical characteristic isn’t especially important to the discussion of brake bias/balance. I just thought it worth mentioning while we were addressing various physical principles of fluids since they also apply to other areas of the vehicle, most conspicuously, the fuel system.

 

So then reputable companys that supply brake kits are wrong in including a proportioning valve?

 

That’s not at all what I said.... maybe it wasn’t clear, a proportioning valve does not replace properly matched components, it is used with matched components. I think to many people think they can throw mismatched parts together and the proportioning valve will magically make it work.

Also I wonder how many people understand not all proportioning valves are the same, where the split point is etc.


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seems to me that every brake conversion kit out there are set up to use GM metric calipers
and a proportioning valve , no matter what the rear drums or dual master may be !!!!
what percentage of these cars would you deem safe !!!!

 

Both 3/16" and 1/4" lines are adequate for the job, but changing from a 3/16" to a 1/4" line is a step in the wrong direction.[especially if the OP is running a single M/C]

Both those lines have a 0.028" wall thickness, so the smaller line has a higher percentage of steel to ID ratio [therefore can withstand higher working pressures]
Attached is a chart for both Steel and for comparison a chart for copper tubing! one thing is consistent , the smaller the tubing the higher the working pressures.
Steel:

Copper tubing:

A proportioning valve "proportions" by definition the same way a glovebox is only stores gloves by definition
If you put a pressure gauge on the front and rear brake circuits and measured the Fr/Rr pressures [I have]
They would be equal all the way through the pressure range UNTIL the pressure is high enough for the "proportioning valve" to limit any more pressure.
After that level the pressure in the rear circuit stays the same and the front circuit pressures keep climbing with more pedal effort applied [on most cars ,this is at extreme limit braking and weight transfer]

Go and get some gauges and learn something

manufacturers usually have the correct Fr/Rr balance so all 4 wheels brake when there is limited traction in everyday driving .
When traction is ideal , and more pedal pressure is applied [= more G's & Weight transfer] then the "proportioning valve" prevents rear wheel lock up.
If there is too much rear brake bias [due to mismatched components] on slippery surfaces the rear wheels will lock up well before the proportioning valve can limit the pressures. The solution is to proportion the clamping pressures [wheel cylinders]

Traction is what determines the brake force required [pedal pressure is reactive]

The only true non-computerized proportioning system is Twin M/Cs with a balance bar.
I stand by my statement about F**kwits who use a proportioning valve to patch up/fix badly engineered brake systems

 

Good site https://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake2.htm

 

Kerrynzi,
My statements about line size are totally correct. Normal max hydraulic brake line pressure is in the 1500-2000 psi range. I have had full power systems that could go to 3000 psi but with extreme (well over 200 lbs) pedal force. The 1/4" steel line IS perfectly safe, and is used in production as I stated earlier, period. Now, using copper tubing (NOT Cunifer) for brake line IS unsafe!
I've run countless balance tests over the 35 years I dynamically tested brakes, with gauges and light beam recorders initially and eventually a computer collecting very accurate pressure transducer data to record everything in the brake system, so I know first hand how a proportioning valve works, and it's not how you describe.
I've gone, and got some gauges, and learned plenty, thank you.
The valve "proportions" in percentage increasing master cylinder pressure to the rears when the crack point/knee/split point had been reached. That's why a prop valve is labeled with two numbers; split point and percentage.
A simple balance bar does not work like this, but believe what you want, and you probably will.

 

^^^^^^Excellent response V8 Bob. Some people could benefit from being fitted with a 'proportioning valve'.....the function of which would be keeping one's self regard in balance with reality.

 

I never said to use Copper tubing [only a f**kwit would do that] I put it there to show two scenarios where smaller diameter has higher working pressures.
Copper lines which I've seen on trailers will split [I've seen that happen too]

I originally wrote "But a 3/16 line can run higher pressures than 1/4 so for safety run the 3/16"

Why would you change that and step backwards [and stop trying to twist what I said]
It was in response to this [post number 43]

You are wrong about conventional proportioning valves, so don't give out dangerous advice claiming it as gospel

Taken from a brake website
"Conventional proportioning valves should really be referred to as “braking force regulators” or “brake pressure regulating valves.” While their name might imply true proportional control, in reality they provide a combination of the control found in Figures A and B.

Up to certain pressures, these valves allow equal pressure to both the front and rear brakes (à la Figure A). However, once a preset pressure point is reached (600 psi in the example), the rear brake pressure continues to build, but at a slower rate (or slope) than the front brake pressure. Figure C displays this for us quite clearly."

I would suggest you should get a Wilwood proportioning valve [the most common inline type] and dismantle it and see how it works.
Wilwoods only advantage is they have a very wide adjustment range

 

The way Kerrynzl describes a proportioning valve is my understanding of how it works as well.

Modern disk/disk systems have no need for one as we can control brake bias with caliper piston size, the reason we need them with drums in the rear is the fact that they are servo acting and will lock up.

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You can put different size wheel cylinders in for the same effect. or alter the co-efficient of friction by trimming the shoes .
But the easiest way is larger callipers instead of reducing the rear brake torque.
The best way is two M/C's with a balance bar.

A Wilwood proportioning valve will get some "creeping up" when the pressure goes over the adjusted limit. But old British Girlings don't do this at all.
I have converted old Austin Girling proportioning valves to fully adjustable years ago [a simple process once you've been inside them]

As I am writing this, I am in the process of re-routing the brake lines and adding a rear proportioning valve to my Race-Car.[ FR500C Mustang]
The brake bias is perfect in my race-car already AND we always brake "on the conservative side of having an accident"
My car is getting prepped for endurance racing , so what we are doing is dialing in more rear bias for Wet conditions ,then using the proportioning valve to limit rear braking fro Dry conditions.
If there is rain mid race, I can open up the proportioning valve to have more rear bias for wet conditions.
In the wet ,there is always the risk of front brake lock up [well before maximum G's]

Now the reason I'm telling you all this.....Is because I've seen many a Car guy put the biggest rotors and callipers on their car to improve it.
But what they end up with is 2 wheel brakes only when driving in slippery conditions [when you need the most traction]

It is the tyres that stop the car.........so we need to think from the tyre footprint back to the drivers foot [which is opposite to what most brake threads are about.... "too much pedal travel, or brakes too hard"]

 

Some disc/disc systems did use a proportioning valve, along with ABS. The '89 T-Bird Super Coupe is just one example, and one I spent much time in during brake development. Proportioning valves themselves became obsolete in the '90s when ABS matured enough to fully assume that function.

 

Yes, I made a general statement.


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Please explain how my advice is wrong and dangerous. My explanation, although maybe not worded the best, is very close to the above. The "slower rate" is in fact a percentage (hence a definition of proportioning). Common percentages were, If I remember correctly, .27, .43, .59. So the valve would be labeled by split pressure, then percentage: 500/43, 400/27 and so on. I think the Wilwoods, and KH valves I use are .27.

 

I am now thinking my 1927 model T, capable of 50 mph with less than 1 sq ft of tire contact with the road , yes all 4 tires is less than 1 sq ft , us now over engeneered LOL
GREAT info here though !!!!

 

I'm glad I read this thread ...kinda

 

yep and add the fact it is a standard shift and it comes back to the question: how does it stop now?

 

Most cars here that are rear drum are going to have Bendix style brakes most manufactures went to them because they required less force to apply. When car makers went to front disk they used proportioning valves. More than likely so the could run the same rear brakes as the front drum cars. Adjustable proportioning are the best fix we have. Even if you ran a complete copy of a factory brake system the weight distribution of you car can mess it all up.

 

Whelp, gonna' "stop" here and clicky my finger, to not miss anymore of this thread. Careening over the cliff of braking system education. Great seats !!!

 

There are a few vehicles that have OEM adjustable proportion valves.
No knobs but with linkage to rear suspension and react with different rideheight bases on the payload or cargo. When that mini van has 7 passengers it needs a different rear bias than when it's empty.
These valves alter the brake system proportionately to the variable loads. The also react to front end dive and weight transfer when the rear unloads.

 

For the application in question, I would keep it very simple and use a distribution block instead of a proportioning valve. I use an aftermarket one in my car, discs up front and drums out back. It has a rear-bias adjuster in it, which I have not had to touch.

 

This my opinion.
If you run front disks, use a double master with all the valves, blocks and doo dads......(like the master's donor car)
If you run 1940s drums all the way around use the 1940s master.
Do not run disks on the 40's master.
Go one way or the other.

One concern I have is the OP stated the '40s master was firewall mounted. It may be fine but these were mounted under the floor. Is the pedal throw and leverage correct?