Proportion Valves for Brakes

[Morris]

There seems to be a different opinion of what a Proportion Valve does in the brake system.
I've worked with Mac Tilton back in the 70's and 80's and let me explain what a Proportion Valve is suppose to do. Remember Back in those days, we didn't have the Adjustable Balance Bar on the Brake Pedal back then. We needed to reduce the pressure on the rear brakes to prevent them from locking up when we got on them real hard. I'm only going to talk to the Proportion Valve many of you use on your existing Cobras since most of them are hand built and people just don't understand what they are doing when installing a Proportion Valve.

This is the Knob of a Tilton Proportion Valve





Think of a Round Housing with a Ball Bearing and Spring inside the housing, then cap the other end of the housing and put a screw with a knob on it so that when you screw the knob in.... it compresses the spring to the point that the ball bearing plugs the orifice that is coming into the bottom of the housing. So if you run Brake fluid into the housing under the orifice it can go out the other in of the Tee Housing or up into the Orifice and push against the Ball and Spring. Turning the knob will make the spring compress against the Orifice and move it up or down in the housing, if you back the spring out, and you apply the brake pedal, the fluid will go to the brake calipers and then based on where the Proportion valve is set the pressure will back up into the orifice and the spring will give and lower the pressure applied to the calipers. If you screw the Proportion Valve all the way down .... when you step on the Brake Pedal ... the brake fluid will go to the caliper and then the spring will not give, so you will get all of the pressure the rear master cylinder is putting out to the Caliper.
So the proportion valve is just a valve with a spring and ball bearing in it and based on its spring pressure is how much rear brake you are going to get before it releases the pressure into the spring loaded proportion valve. Wewww...




As you can see in this photo.... there is only a input and output to the Proportion Valve.

So let's say you have your foot on the brake pedal and are pushing hard and you have gauges on the front calipers and the rear calipers. With the Tilton Proportion Valve screwed all the way in .... the Gauges will read 1000#lbs on the front and 1000#lbs on the rear.
Now same situation but you unscrew the Tilton Proportion Valve half way ... the reading on the gauges will read 1000#lbs on the front, but the rear will read 500#lbs on the rear because the spring in the proportion valve will retract the amount you have unscrewed the Valve so that as the caliper starts to clamp on the Rotor, it can't clamp with as much force because the spring is moving not letting the caliper get all of the pressure coming from the master cylinder.



So now you need to have the valve close to you so you can adjust the rear bias of the brakes while running the the vehicle....

There are many way to see what is going on with you brake bias.... That's a hole additional subject. That we'll get into later.

I hope this helps out the guy's that have a single Master Cylinder.... understand what is going on with their proportion valve.

Morris

[Snake2998]

Interesting post - thanks. In general Cobras with Jag suspension and brakes are way under braked at the rear and either need much bigger rear caliper pistons or a much smaller rear MC to balance the brakes. Some in South Africa put the proportioning valve on the front circuit and say it makes a huge improvement to braking on the track (Generally not advised by makers of these valves so approach with caution and much careful testing)

[Morris]

Originally Posted by Snake2998

Interesting post - thanks. In general Cobras with Jag suspension and brakes are way under braked at the rear and either need much bigger rear caliper pistons or a much smaller rear MC to balance the brakes. Some in South Africa put the proportioning valve on the front circuit and say it makes a huge improvement to braking on the track (Generally not advised by makers of these valves so approach with caution and much careful testing)

Snake

I would never put a Proportion Valve on the front Brake circuit......especially since 60% to 70% of braking is done on the front brakes......balancing the brakes on a road racing car is very important to the stopping as well as the handling of a car.....installing a Proportion Valve on the front circuit is automatically reducing the effectiveness of the front brakes.....and could effectively reduce the overall braking.....

A lot of guy’s crank in more rear brake bias to help the front of the chassis turn in faster....very common in all race cars....because you don’t transfer as much weight to the front when braking, thus, allowing better turn in the corner.....because there’s less push on the front tires......or less weight transferred to the front.

First you have to balance the Master Cylinders Front and Rear.....smaller Master Cylders provide more pressure but less volume.......larger Master Cylinders provide less pressure but more volume.....

For those with Single Master Cylinders...then you need the Proportion Valve in the Rear Circuit to assist in overall braking first ...then once they are balanced properly, you can start trying to add rear brake to help the front turn in better.

How do you know how the brakes are operating???

The easiest and most reliable method is to use temperature paint on the rotors....like paint a H pattern on the rotors starting at 900*degrees and then 1000*degrees, then 1100*degrees, then 1200* degrees.....on all of the rotors....then go out for some laps and use the brakes vigorously as normal.....when you come in and remove the tires & wheels.....look at the rotors and see what temperature the fronts are running and the rears are running....thus you will then know how hot the rotors are running .....

You shoot for about a 200* degree difference front to rear....like 1000* degrees on the front & 800* degrees on the rear.....in our racing on tracks we would run about 1150*-1200* degrees on front......and 900*-1000* degrees on the rears.....then if I needed to get more turnin on certain corners I’d crank in a couple turns on my brake balance bar.....none of you well reach these high numbers ...so maybe you should start with some lower numbers....and use the same ideas.....

Sorry for the long post ...but there is no short way to say all of this kind of info.....

Morris

[hauss]

Originally Posted by Morris

Snake

I would never put a Proportion Valve on the front Brake circuit......especially since 60% to 70% of braking is done on the front brakes......balancing the brakes on a road racing car is very important to the stopping as well as the handling of a car.....installing a Proportion Valve on the front circuit is automatically reducing the effectiveness of the front brakes.....and could effectively reduce the overall braking.....

A lot of guy’s crank in more rear brake bias to help the front of the chassis turn in faster....very common in all race cars....because you don’t transfer as much weight to the front when braking, thus, allowing better turn in the corner.....because there’s less push on the front tires......or less weight transferred to the front.

First you have to balance the Master Cylinders Front and Rear.....smaller Master Cylders provide more pressure but less volume.......larger Master Cylinders provide less pressure but more volume.....

For those with Single Master Cylinders...then you need the Proportion Valve in the Rear Circuit to assist in overall braking first ...then once they are balanced properly, you can start trying to add rear brake to help the front turn in better.

How do you know how the brakes are operating???

The easiest and most reliable method is to use temperature paint on the rotors....like paint a H pattern on the rotors starting at 900*degrees and then 1000*degrees, then 1100*degrees, then 1200* degrees.....on all of the rotors....then go out for some laps and use the brakes vigorously as normal.....when you come in and remove the tires & wheels.....look at the rotors and see what temperature the fronts are running and the rears are running....thus you will then know how hot the rotors are running .....

You shoot for about a 200* degree difference front to rear....like 1000* degrees on the front & 800* degrees on the rear.....in our racing on tracks we would run about 1150*-1200* degrees on front......and 900*-1000* degrees on the rears.....then if I needed to get more turnin on certain corners I’d crank in a couple turns on my brake balance bar.....none of you well reach these high numbers ...so maybe you should start with some lower numbers....and use the same ideas.....

Sorry for the long post ...but there is no short way to say all of this kind of info.....

Morris

I think they are referring to a line lock

[Ron61]

Morris,

That is a very informative post and many who really don't understand what those valves do should read it and look at the pictures.

Ron

[t walgamuth]

On my old Lotus 7 replica there was proportioning valves one for the front and one for the rear. In autocross you find much different track conditions and need to be able to do whatever is needed to balance the brakes the way you want them.

What works perfectly on dry hot concrete will make the rear loose on cold asphalt and you'll have a problem.

It is easy to forget about the adjustment and blame the driver too. I have had days where I never figured it out until after the event was over.

[patrickt]

Good write up. I've never owned a car with an adjustable proportioning valve, that I know of at least. ERAs use dual master cylinders with an adjustable bias linkage which, when properly set up, supposedly gives you true linear proportioning, or so I'm told. I can't say I've ever measured them. I would think Kirkhams use a similar set up. Even with cars that do not have an undercarriage brake box, a dual MC bias linkage wouldn't be all that hard to fabricate in. If you were doing any sort of serious racing in your car, why wouldn't you want that? Or if you're manufacturing a Cobra that's approaching six figures as a turnkey, why would you even think about using a proportioning valve instead of a dual MC bias linkage? Tilton MCs are less than a hundred bucks a pop, and linkage is just linkage....

[Morris]

Originally Posted by hauss

I think they are referring to a line lock

Line Lock is used in Drag Racing.... we are discussing Road Racing.

And I believe he said that Some in South Africa use Proportion Valves on the Front Circuit..... and that is bad as it reduces the braking on the Front where it is needed most.

Or they are not going fast enough to know the difference.

[patrickt]

Here's a pic of my dual MC bias linkage setup and, as all true race car type guys like us know, the more grease you use on anything the better it works.

[cycleguy55]

Assuming I understand this correctly, a bias bar setup will maintain the same F/R bias throughout the range of braking pressures (Figure B in linked article).


A proportioning valve, OTOH, 'caps' or limits the pressure applied to the rear brakes. IOW, if the pressure bias built in to the braking system with a proportioning valve was 60/40 F/R, that bias would be maintained until the 'kneepoint' of the proportioning valve is reached, at which point the front brake pressures continue to rise with pedal pressure, but rear pressures level off (Figure C in linked article) to prevent rear wheel lock-up.


There's more in this article from StopTech - certainly worth a few minutes to read: Proportioning Valves

Thoughts?

[Morris]

The Thread was started because many folks had inline Master Cylinders and Proportion Valves and didn't really understand how it works .... I just explained how it works for the people that use them....

The more advanced Group will go with the Balance Bar in the Brake Pedal and use a Knob to adjust Front to Rear Bias of the Brakes.... and that is done by moving the Pivot point in the Brake Pedal towards the Master Cylinder that you want more pressure from.

And some of us will use Both as we have the ability to use the Balance Bar for a major adjustment and a Proportion Valve for Fine tuning.



Here we see the Dash and below the Dash is a Central Dash that is much Thicker then the dash. mainly because the Standard Dash is so thin that pulling or pushing on the dash will cause it to flex and not operate the device you are trying to open or close ie; Fire System or even turn the knobs for Power or Brake Bias Adjustment.



Here's a much closer photo of the Central Dash, it's made out of 1/4" Thick T-6 Aluminum so there is no Flexing going on....and of course you see the Brake Bias Knob to move the Spherical bearing in the Brake Pedal to one side or the other in the brake pedal... (To the Front master cylinder or Rear master cylinder), and the Main Power Switch as well as the Fire System Knob

[Morris]

There's a lot going on in this photo



First you see the cable going from the Brake Bias Knob to the shaft of the spherical bearing in the brake pedal so it can be moved... base on turning it to the right or left to bias more pressure to the Front or Rear Master Cylinder.

Also you see the Throttle Pedal with a Stop on the end of the pedal and there is a stop on the back side of the Clutch pedal as well. These Stops are very much needed as you don't have time to feel for the stop on the carb or FI. or on the Clutch... just adjust the stops so the carb or F.I. go to the Stop on the Unit. or set the Clutch so the stop goes to release the Clutch at the proper amount without any over travel.



Here you'll notice that we don't have a Dead Pedal.... there just isn't enough room in a Cobra to have one .... So like the Formula Cars we put in a 2" piece of SS.. to rest our foot on and not on the Clutch pedal.

So when you get to the level of Racing I was at you will use both the Brake Bias and a Proportion Valve to adjust the brakes for weight transfer and trail braking to get around a corner as fast as you can... and it works quite well.

[Morris]

Originally Posted by patrickt

Here's a pic of my dual MC bias linkage setup and, as all true race car type guys like us know, the more grease you use on anything the better it works.

Patrick

Have you ever been off track..... ?? cause that would be a disaster.... you might want to cover the Master Cylinders and BTW....Clean the Grease off of the Rod ends .... they just want Light weight lubricant and protection...

All of the dirt and rocks will go right to the grease...especially on the Drivers side front wheel.

Just Saying...

[patrickt]

That pic is with the aluminum box removed (it's totally enclosed otherwise). Even as stupid as I am, I wouldn't run it like that out in the open. Well, I might, but Bob P. would revoke my ERA license....

[patrickt]

This is the brake box cover that goes over it all. This pic was taken after I had a brake fluid leak inside the box. I always use the BLUE Ate Superblue fluid so it's obvious what fluid it is, which isn't always easy. They outlawed it in the US a few years ago, but I have it shipped to me from Germany. But I do appreciate you lookin' out for me, I need all the help I can get.

[Morris]

Patrick

Did any of that dirt in your cover get on the push rods with all of the grease??

That’s why you only want to use light weight WD40 or Kroll spray lubricant type to lubricate the helms and especially the Spherical bearing in the brake bias bearing......so it can easily be adjusted...as it will only turn when you take your foot off of the pedal.....

[Morris]

Originally Posted by cycleguy55

Assuming I understand this correctly, a bias bar setup will maintain the same F/R bias throughout the range of braking pressures (Figure B in linked article).


A proportioning valve, OTOH, 'caps' or limits the pressure applied to the rear brakes. IOW, if the pressure bias built in to the braking system with a proportioning valve was 60/40 F/R, that bias would be maintained until the 'kneepoint' of the proportioning valve is reached, at which point the front brake pressures continue to rise with pedal pressure, but rear pressures level off (Figure C in linked article) to prevent rear wheel lock-up.




There's more in this article from StopTech - certainly worth a few minutes to read: Proportioning Valves

Thoughts?

This proves what I was saying....Very good illustration...and shows why we used both to fine tune the response of the chassis in the corners.....but it takes a lot of experience to get to this level......

[patrickt]

That big long globby thing is actually not dirt, it was a dribble line of RTV that was just gooed on there and had its origins somewhere in the bowels of ERA. All the rods looked nice and clean but you'll notice that I have "dual hose clamps" on the Tilton brake hose. The original tension clips were just not holding anymore after I had used a pad spreader to force a little fluid back up the lines. Instead of travelling all the way up to my pretty black Girling reservoirs the fluid took a shortcut out the tension clamp and they just would not hold anymore. Soooo, I relied on the tried and true screw tighten clamps along with the tension clamps. That worked. Half the fun of my car is just keeping her from leaving puddles in the garage.