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I had this proportioning valve on the last brake set up I had and really couldn't tell if it was doing anything so I've done some testing and I think the results might be helpful to others.

I hobbled together some fittings that were air tight,  Wilwood says this unit will decrease the amount of braking pressure by 50% with the knob turned all the way up to the top of the threads, well I found that 33% was the best I could get from it.  The proportioning valve only has a 1000 miles use on it and is very clean inside.  I started with 90psi which resulted in 60psi for the rear wheels, with one full turn of the knob CW the pressure came up to 75psi, with one more full turn brought the pressure up to the full 90psi,  so all of it's proportioning takes place in the top two turns and there is still 9 more full turns left until the knob bottoms out.

So why are those 9 other turns on there? Just to confuse us I guess. So disregard the bottom 9 turns as they do nothing,  33% decrease is more than enough for me to work with.

Now compressed air is not brake fluid so I suppose the results might be different, how much?  I don't know enough about fluid dynamics to say one way or the other.

3rd pic at 60psi, 4th pic one turn down, 5th pic 2 turns down.

 

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IMG_0840.JPG

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Posted (edited)

I think your problem is that you're doing the equivalent of testing a cooling system thermostat by putting it in a pot of water on an electric blanket. Autometer brake pressure gauge goes to 2000 psi. I don't know what "normal" brake pressures are, but I suspect that you're WAAAAAAAY too low to test them in this manner. 

https://www.autometer.com/2-5-8-brake-press-0-2000-psi-no-tubing.html

 

EDIT--If you put those gauges in front and rear and then turned the dial, then you could get useful info. FWIW I had a brake system where adjusting the prop valve made no difference at all, using 4x4 front calipers and early ZX rear disc. The problem was that the rears were so undersize that it didn't need to be reduced at all. If that's the case for anyone, the solution is bigger rear brakes or smaller fronts, NOT to put the prop valve in the front circuit. 

Hydraulic prop valves are not "proportioning" so you don't get a linear 70% or whatever amount of the pressure. They have a knee, after which the pressure falls off. What this means is that if you put one in the front brake circuit, the harder you step on the brakes the less front brake pressure you will get. Anyone who has looked at brake balancing knows that the harder you step on the brakes, the more weight transfers to the front, the less pressure you want in the rear. So it's a really bad idea to put a prop valve in the front brakes. 

Edited by JMortensen

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Posted (edited)

Thanks for the link Jon, it would be interesting to get that meter and test in a real setting.  I'm not sure where you got the idea from but I'm not using the prop valve on the front brakes, I will be using it to decrease braking pressure to the rears as they are locking up before the fronts.

I just installed the Silvermine front and rear kits,

https://www.silverminemotors.com/datsun/datsun-240z/brake-upgrades/240z-260z-280z-front-wilwood-brake-upgrade-kit

and,

https://www.silverminemotors.com/datsun/datsun-240z/brake-upgrades/datsun-240z-260z-280z-rear-dual-caliper-wilwood-brake-upgrade-with-dedicated-cable-handbrake-caliper-stock-cable

and although I haven't completed the bedding in process yet I can tell the rears are getting too much of the balance.

I thought compressed air might not  be a good substitute for brake fluid but it's what I had on hand.

Edited by grannyknot

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Posted (edited)
1 hour ago, grannyknot said:

Thanks for the link Jon, it would be interesting to get that meter and test in a real setting.  I'm not sure where you got the idea from but I'm not using the prop valve on the front brakes, I will be using it to decrease braking pressure to the rears as they are locking up before the fronts.

I just installed the Silvermine front and rear kits,

https://www.silverminemotors.com/datsun/datsun-240z/brake-upgrades/240z-260z-280z-rear-wilwood-brake-upgrade-kit-large-calipers

and,

https://www.silverminemotors.com/datsun/datsun-240z/brake-upgrades/datsun-240z-260z-280z-rear-dual-caliper-wilwood-brake-upgrade-with-dedicated-cable-handbrake-caliper-stock-cable

and although I haven't completed the bedding in process yet I can tell the rears are getting too much of the balance.

I thought compressed air might not  be a good substitute for brake fluid but it's what I had on hand.

I can tell you off the bat that you're going to need some serious help to get the rears to come in line, and even with a dual master setup, you might always have a rear bias with this setup. What master cylinder(s) are you using?

 

On edit: You've linked two rear kits. What front kit did you get? 

Edited by Ben280

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Posted (edited)
1 hour ago, Ben280 said:

On edit: You've linked two rear kits. What front kit did you get? 

Thanks for catching that Ben, I have fixed the first link, this is the front kit, https://www.silverminemotors.com/datsun/datsun-240z/brake-upgrades/240z-260z-280z-front-wilwood-brake-upgrade-kit

I'm using the 15/16" M/C

Edited by grannyknot

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Posted (edited)

Ahh ok. You've got WAY too much rear brake. The front pistons are a bit of a mis-matched for the size of the rear pistons, fronts are small, rears are large, relatively speaking. Since the MC equally powers both brake circuits, the clamping force at the rear is higher due to the increased piston area. If you have any of the factory stuff in the brake circuits, this will alter your results. 

 

Right now, based off Wilwood's numbers for the Superlite front (4x 1.12" pistons) and the Dynapro rear (4x 1.38" pistons) you have a 60% rear bias. Ideally that would be flipped. If you max out that prop valve and cut the rear pressure in half, you'll end up with a 56% front bias. 

 

Couple links included below for further reading on the exciting world of brake pressure math!

 

https://www.tceperformanceproducts.com/bias-calculator/

https://www.joesracing.com/master-cylinder-math/

Edited by Ben280
More numbers!

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Sorry, I know you didn't come here asking about your brake ratios, but the links you posted got me curious. I went through a similar sizing adventure, although I am able to use different sized master cylinders to solve my bias issues. 

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I didn't mean to say that your brake system was one way or the other, more just a general warning to anyone who might read this that you don't want a prop valve in the front circuit, that's all. 

If it helps 1.75 pistons in front and 1.38 pistons in rear is what Arizona Z Car used to sell (maybe still does???) with a hydraulic prop valve.

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So question to those who know things about things.

 

Let's say a person has the Toyota S12+8 calipers up front (the solid rotor variety, not the vented kind) and 240sx calipers in the back.

 

Should that person use a proportioning valve at all, or should I...I mean, "that person", use it, and dial it down as far as it'll go?

 

(Obviously the prop valve would link into the rear brake system only)

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Posted (edited)
4 hours ago, Neverdone said:

So question to those who know things about things.

 

Let's say a person has the Toyota S12+8 calipers up front (the solid rotor variety, not the vented kind) and 240sx calipers in the back.

 

Should that person use a proportioning valve at all, or should I...I mean, "that person", use it, and dial it down as far as it'll go?

 

(Obviously the prop valve would link into the rear brake system only)

 

I have this set up on my 72 240Z. The front to rear bias is 60% front and 40% rear. A proportioning valve reduces pressure which would make your rear brakes less effective.  You absolutely do not need a proportioning valve. So don't install a proportioning valve.

 

My set up includes a 15/16 in 280ZX MC and a 280Z 9 in. dia. booster. Pads are Carbotech  AX6.  Car is daily driver. Stops like a stock car.

Edited by Miles

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19 hours ago, Ben280 said:

Sorry, I know you didn't come here asking about your brake ratios, but the links you posted got me curious. I went through a similar sizing adventure, although I am able to use different sized master cylinders to solve my bias issues. 

Not at all Ben, I appreciate the help. I was told by the owner of Silvermine that the kits I chose would be perfect without a prop valve so I didn't bother to hook it up, well I'll install it and see if it helps.  The only reason I bought those particular kits was because I was told they were a matched set with perfect bias for the Z.  Thanks

3 hours ago, Neverdone said:

So question to those who know things about things.

 

Let's say a person has the Toyota S12+8 calipers up front (the solid rotor variety, not the vented kind) and 240sx calipers in the back.

 

Should that person use a proportioning valve at all, or should I...I mean, "that person", use it, and dial it down as far as it'll go?

 

(Obviously the prop valve would link into the rear brake system only)

As Miles says, don't bother. That is the setup I just replaced with the Wilwood setup.

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On 5/19/2020 at 2:34 PM, grannyknot said:

Not at all Ben, I appreciate the help. I was told by the owner of Silvermine that the kits I chose would be perfect without a prop valve so I didn't bother to hook it up, well I'll install it and see if it helps.  The only reason I bought those particular kits was because I was told they were a matched set with perfect bias for the Z.  Thanks

As Miles says, don't bother. That is the setup I just replaced with the Wilwood setup.

 

Depending on what is left in the factory system for the rear circuit, it might be alright. Drum rears use a lot less pressure than calipers, which might be why the rears seem to be oversized. Worth looking into more before cutting in the prop valve. I don't THINK Edan would flat out lie to you, but he might have made some assumptions about what you have going on. 

 

Also, it would be worth verifying based on the Wilwood boxes/part numbers your piston size, as the numbers listed on the Silvermine site don't correlate with the numbers on the Wilwood site. But parts change and I'm relying on photos that might be out of date!

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21 hours ago, Ben280 said:

Worth looking into more before cutting in the prop valve.

I previously removed the original prop valve so it might be worth reinstalling it to see what the bias is.  I just remembered I have these sitting the shelf, I ordered one from Amazon and about 2 months later a 2nd one showed up.

By tapping these in just before the calipers front and rear I could get some hard numbers for the stock prop valve and the Wilwood prop valve.

 

IMG_0862.JPG

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Posted (edited)

I spent the day making up brake lines to fit the 3 configurations, bleeding each one and testing while trying to record it all on video.

As @JMortensen suggested, compressed air is NOT a good substitute for brake fluid when testing a prop valves as you will see. So to any future readers please ignore my conclusions in the first post. The Wilwood prop valve acted exactly as you would assume it would with each turn cutting off a bit more pressure until the minimum was reached.

 

This testing was done on a 72/240z with a new 15/16" Master Cylinder, rebuilt 280z brake booster, all new Cunifer brake lines, SS flex hoses and Wilwood 120-6816 4 piston calipers  on the rear. The fronts brakes were not tested.

 

- the first configuration was 15/16" MC straight through to the calipers with NO prop valve and I assume no vacuum booster assist as the engine was not running.  1200 psi pushing as hard as I could.

- the second configuration was with the stock 240z prop valve installed,  600 psi pushing as hard as I could.

- the third was with the Wilwood 260-12627 prop valve installed and the stock prop valve removed, you’ll notice that with the Wilwood prop valve installed with the valve wide open there is a 100 psi decrease in the total pressure down to 1100 psi from 1200 in the 1st video. 

wide open, 1100psi

1 turn closed, 1050psi

2 turns           950psi

3 turns           950psi

4 turns            875psi

5 turns            750psi

6 turns           750psi

7 turns          650psi

8 turns          600psi

9 turns          600psi

10 turns        575psi

10.5 turns     575psi

I took it out for a run with the prop valve turned all the way closed to 575psi and I that’s just about right. I warmed up the brakes a bit then tried a panic stop, PS rear lock up but none of the others. Tried the same thing again and the DS front locked up but none of the others so I’m pretty close but will continue to test and play with it.  So the front brakes are now getting 1200psi and rear 575psi.

 

https://youtu.be/FWQ2V-w1Av4

For some reason the 3rd vid won't embed but the link is above.

Edited by grannyknot
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Thanks Ben, somehow I deleted the second video from the previous post so I have put it back in, that's the test with stock prop valve.

Exactly half of the pressure from the MC, the stock prop valve was disassembled, cleaned and rebuilt just before this test so I know it's working properly.  I probably could have left it on and been just fine for balance.

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I wish I could remember what my setting are , but I got them to lock up correctly and haven’t touched it in years . I run Wildwoods all around . I do remember that it was wayyyy biased up front . 

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9 hours ago, madkaw said:

I wish I could remember what my setting are , but I got them to lock up correctly and haven’t touched it in years . I run Wildwoods all around . I do remember that it was wayyyy biased up front . 

How did you even that out, prop valve on the front?

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