Bias/Proportioning Valve?

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Clatter
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Bias/Proportioning Valve?

Post by Clatter » Thu Nov 09, 2017 9:26 pm

Having 944 brakes on my Fastback has me wondering...

1. 944 and Fastback have different bias needs.
Mine is especially rear-heavy.. Type 4 and 915 trans.

2. Since most are setup to stop rear brakes from locking, then install into the rear circuit.
Because my car should need more rear - install the valve into the front circuit??

3. Metric fittings.. Anyone make a bias valve metric?

If you have ever run one of these things,
What did you think of it?

How about this one?
http://www.mcgillmotorsport.com/adjusta ... r-type-678
"Oh, You don't need to do all that... The valve seats are just going to fall out of it anyway!"
- Doug Ellsworth

Beginners' how-to Type 4 build thread ---> viewtopic.php?f=1&t=145853

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Jadewombat
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Re: Bias/Proportioning Valve?

Post by Jadewombat » Thu Nov 09, 2017 10:22 pm

What master cylinder are you using?

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Clatter
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Re: Bias/Proportioning Valve?

Post by Clatter » Thu Nov 09, 2017 10:45 pm

Stock Type 3, unless it doesn't give good results..
"Oh, You don't need to do all that... The valve seats are just going to fall out of it anyway!"
- Doug Ellsworth

Beginners' how-to Type 4 build thread ---> viewtopic.php?f=1&t=145853

Ol'fogasaurus
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Re: Bias/Proportioning Valve?

Post by Ol'fogasaurus » Fri Nov 10, 2017 12:14 am

Have you looked into an adjustable proportioning valve. Not good for all situations but might be an option.
Lee

My opinion is worth slightly less than what you paid for it.

Ol'fogasaurus
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Re: Bias/Proportioning Valve?

Post by Ol'fogasaurus » Fri Nov 10, 2017 2:22 pm

https://www.bing.com/shop?q=adjustable+ ... 99E8DDF4D5

So many styles to look at and decide if it is right for you.

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Clatter
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Re: Bias/Proportioning Valve?

Post by Clatter » Sat Nov 11, 2017 10:36 pm

So,

If my brakes are from a 944, with near 50/50 F/R weight bias,
And I'm putting them into a car that's tail-heavy,
I should put the valve into the front circuit,
Instead of the rear circuit..

Right?
"Oh, You don't need to do all that... The valve seats are just going to fall out of it anyway!"
- Doug Ellsworth

Beginners' how-to Type 4 build thread ---> viewtopic.php?f=1&t=145853

Ol'fogasaurus
Posts: 13213
Joined: Tue Nov 14, 2006 1:17 am
Location: Just north of Seattle

Re: Bias/Proportioning Valve?

Post by Ol'fogasaurus » Sat Nov 11, 2017 11:06 pm

Basically, the proportioning valve slows down the amount/volume of the fluid to the brakes it is attached to but only by a shade, that speed is controlled by the internal of the valve itself.

The adjustable version allows one to "tune" the bias a bit by a knob that controls the amount/volume of fluid it allows to pass.

If you put a valve on the front brakes then their full application is slowed and the rears apply first. Putting them on the rears allow the front to apply first.

Overly simplified description but does this help?
Lee

My opinion is worth slightly less than what you paid for it.

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raygreenwood
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Re: Bias/Proportioning Valve?

Post by raygreenwood » Mon Nov 13, 2017 8:40 pm

Ol'fogasaurus wrote:
Sat Nov 11, 2017 11:06 pm
Basically, the proportioning valve slows down the amount/volume of the fluid to the brakes it is attached to but only by a shade, that speed is controlled by the internal of the valve itself.

The adjustable version allows one to "tune" the bias a bit by a knob that controls the amount/volume of fluid it allows to pass.

If you put a valve on the front brakes then their full application is slowed and the rears apply first. Putting them on the rears allow the front to apply first.

Overly simplified description but does this help?

This really depends on what kind of proportioning valve it is.....and proportioning is different from bias.

Some factory dedicated proportioning valves like those used on 411, 412, 914, some BMW, Audi and Mercedes ....actually do not limit volume to the brakes being proportionally regulated....until a certain pressure is reached. Then it maintains that pressure and does not allow it to rise further.

Some others...more sophisticated factory ones....can actually further reduce rear brake pressure due to body to rear axle angle to further respond to say....a more heavily loaded car.

But brake BIAS....true brake bias.....does not mess with pressure. It adjusts TIMING.....or "onset" of braking. For instance most cars have a front bias.....wherein when the pedal is pushed the front brakes start braking first even if they are running with the exact same pressure as the rear.
The pedal will move the front circuit piston X distance before the rear circuit gets any movement at all.

On aftermarket systems for dull custon cars....one might have actual seperate single circuit MC's for front and rear. The pedal moves a single pushrod that has an adjustable bias bar....tbat does not alloe contact with the other circuit until it has moved X distance.

You you can do it hyraulically....with what is eszentially a check valve that does not allow any pressure to the rear (or whichever ciruit you are delaying)....until the lead circuit reaches X amount of pressure.

The actual factory dual circuit MC's do this biasing much as you described. The front circuit which is "normally" in contact with the pushrod....will have a softer spring than the inner rear circuit piston. So it will move X distance until it generates enough spring pressure to overcome the spring pressure on the inner piston snd start it moving.
Ray

Ol'fogasaurus
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Re: Bias/Proportioning Valve?

Post by Ol'fogasaurus » Mon Nov 13, 2017 9:23 pm

Thanks Ray. As I said it was an overly simplified description. You did say some things I did not know though. :oops:

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raygreenwood
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Re: Bias/Proportioning Valve?

Post by raygreenwood » Sat Nov 18, 2017 1:21 am

Ol'fogasaurus wrote:
Mon Nov 13, 2017 9:23 pm
Thanks Ray. As I said it was an overly simplified description. You did say some things I did not know though. :oops:
No sweat!.....I learned the difference the hard way tinkering with a,Saab....and almost rolled it! :lol:
Ray

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